01721nas a2200169 4500008004100000245003000041210003000071260001400101520125300115100001801368700002001386700002801406700002801434700003501462700001701497856003701514 2024 eng d00aAgnostic Phase Estimation0 aAgnostic Phase Estimation c2/29/20243 a

The goal of quantum metrology is to improve measurements' sensitivities by harnessing quantum resources. Metrologists often aim to maximize the quantum Fisher information, which bounds the measurement setup's sensitivity. In studies of fundamental limits on metrology, a paradigmatic setup features a qubit (spin-half system) subject to an unknown rotation. One obtains the maximal quantum Fisher information about the rotation if the spin begins in a state that maximizes the variance of the rotation-inducing operator. If the rotation axis is unknown, however, no optimal single-qubit sensor can be prepared. Inspired by simulations of closed timelike curves, we circumvent this limitation. We obtain the maximum quantum Fisher information about a rotation angle, regardless of the unknown rotation axis. To achieve this result, we initially entangle the probe qubit with an ancilla qubit. Then, we measure the pair in an entangled basis, obtaining more information about the rotation angle than any single-qubit sensor can achieve. We demonstrate this metrological advantage using a two-qubit superconducting quantum processor. Our measurement approach achieves a quantum advantage, outperforming every entanglement-free strategy.

1 aSong, Xingrui1 aSalvati, Flavio1 aGaikwad, Chandrashekhar1 aHalpern, Nicole, Yunger1 aArvidsson-Shukur, David, R. M.1 aMurch, Kater uhttps://arxiv.org/abs/2403.0005402447nas a2200169 4500008004100000245005000041210004900091260001300140520194800153100002002101700003302121700002102154700002802175700001702203700002002220856003702240 2024 eng d00aComplexity-constrained quantum thermodynamics0 aComplexityconstrained quantum thermodynamics c3/7/20243 a

Quantum complexity measures the difficulty of realizing a quantum process, such as preparing a state or implementing a unitary. We present an approach to quantifying the thermodynamic resources required to implement a process if the process's complexity is restricted. We focus on the prototypical task of information erasure, or Landauer erasure, wherein an n-qubit memory is reset to the all-zero state. We show that the minimum thermodynamic work required to reset an arbitrary state, via a complexity-constrained process, is quantified by the state's complexity entropy. The complexity entropy therefore quantifies a trade-off between the work cost and complexity cost of resetting a state. If the qubits have a nontrivial (but product) Hamiltonian, the optimal work cost is determined by the complexity relative entropy. The complexity entropy quantifies the amount of randomness a system appears to have to a computationally limited observer. Similarly, the complexity relative entropy quantifies such an observer's ability to distinguish two states. We prove elementary properties of the complexity (relative) entropy and determine the complexity entropy's behavior under random circuits. Also, we identify information-theoretic applications of the complexity entropy. The complexity entropy quantifies the resources required for data compression if the compression algorithm must use a restricted number of gates. We further introduce a complexity conditional entropy, which arises naturally in a complexity-constrained variant of information-theoretic decoupling. Assuming that this entropy obeys a conjectured chain rule, we show that the entropy bounds the number of qubits that one can decouple from a reference system, as judged by a computationally bounded referee. Overall, our framework extends the resource-theoretic approach to thermodynamics to integrate a notion of time, as quantified by complexity.

1 aMunson, Anthony1 aKothakonda, Naga, Bhavya Tej1 aHaferkamp, Jonas1 aHalpern, Nicole, Yunger1 aEisert, Jens1 aFaist, Philippe uhttps://arxiv.org/abs/2403.0482802447nas a2200169 4500008004100000245005000041210004900091260001300140520194800153100002002101700003302121700002102154700002802175700001702203700002002220856003702240 2024 eng d00aComplexity-constrained quantum thermodynamics0 aComplexityconstrained quantum thermodynamics c3/7/20243 a

Quantum complexity measures the difficulty of realizing a quantum process, such as preparing a state or implementing a unitary. We present an approach to quantifying the thermodynamic resources required to implement a process if the process's complexity is restricted. We focus on the prototypical task of information erasure, or Landauer erasure, wherein an n-qubit memory is reset to the all-zero state. We show that the minimum thermodynamic work required to reset an arbitrary state, via a complexity-constrained process, is quantified by the state's complexity entropy. The complexity entropy therefore quantifies a trade-off between the work cost and complexity cost of resetting a state. If the qubits have a nontrivial (but product) Hamiltonian, the optimal work cost is determined by the complexity relative entropy. The complexity entropy quantifies the amount of randomness a system appears to have to a computationally limited observer. Similarly, the complexity relative entropy quantifies such an observer's ability to distinguish two states. We prove elementary properties of the complexity (relative) entropy and determine the complexity entropy's behavior under random circuits. Also, we identify information-theoretic applications of the complexity entropy. The complexity entropy quantifies the resources required for data compression if the compression algorithm must use a restricted number of gates. We further introduce a complexity conditional entropy, which arises naturally in a complexity-constrained variant of information-theoretic decoupling. Assuming that this entropy obeys a conjectured chain rule, we show that the entropy bounds the number of qubits that one can decouple from a reference system, as judged by a computationally bounded referee. Overall, our framework extends the resource-theoretic approach to thermodynamics to integrate a notion of time, as quantified by complexity.

1 aMunson, Anthony1 aKothakonda, Naga, Bhavya Tej1 aHaferkamp, Jonas1 aHalpern, Nicole, Yunger1 aEisert, Jens1 aFaist, Philippe uhttps://arxiv.org/abs/2403.0482801754nas a2200169 4500008004100000245008800041210006900129260001400198520119900212100002201411700002301433700001901456700002901475700002201504700002101526856003701547 2024 eng d00aEfficient and practical Hamiltonian simulation from time-dependent product formulas0 aEfficient and practical Hamiltonian simulation from timedependen c3/13/20243 a

In this work we propose an approach for implementing time-evolution of a quantum system using product formulas. The quantum algorithms we develop have provably better scaling (in terms of gate complexity and circuit depth) than a naive application of well-known Trotter formulas, for systems where the evolution is determined by a Hamiltonian with different energy scales (i.e., one part is "large" and another part is "small"). Our algorithms generate a decomposition of the evolution operator into a product of simple unitaries that are directly implementable on a quantum computer. Although the theoretical scaling is suboptimal compared with state-of-the-art algorithms (e.g., quantum signal processing), the performance of the algorithms we propose is highly competitive in practice. We illustrate this via extensive numerical simulations for several models. For instance, in the strong-field regime of the 1D transverse-field Ising model, our algorithms achieve an improvement of one order of magnitude in both the system size and evolution time that can be simulated with a fixed budget of 1000 arbitrary 2-qubit gates, compared with standard Trotter formulas.

1 aBosse, Jan, Lukas1 aChilds, Andrew, M.1 aDerby, Charles1 aGambetta, Filippo, Maria1 aMontanaro, Ashley1 aSantos, Raul, A. uhttps://arxiv.org/abs/2403.0872901134nas a2200133 4500008004100000245002800041210002800069260001400097520078800111100002100899700002100920700002200941856003700963 2024 eng d00aEncoding Majorana codes0 aEncoding Majorana codes c2/12/20243 a

To implement a quantum error correction protocol, we first need a scheme to prepare our state in the correct subspace of the code, and this can be done using a unitary encoding circuit. Majorana codes are special since any gates that transform such codes must preserve fermionic parity. In this paper, we present an algorithm that uses the stabilizer matrix to compute unitary encoding circuits for Majorana codes. We present two approaches, both of which use a version of Gaussian elimination with row operations replaced with elementary fermionic Clifford operations. One approach uses an additional ancilla mode and works for all Majorana stabilizer codes, while the second approach does not use ancilla but does not work if the total parity is inside the stabilizer group.

1 aMudassar, Maryam1 aChien, Riley, W.1 aGottesman, Daniel uhttps://arxiv.org/abs/2402.0782901993nas a2200205 4500008004100000022001400041245010700055210006900162260001400231490000800245520134600253100001901599700001901618700002001637700001901657700002901676700002001705700002501725856003701750 2024 eng d a1079-711400aHigh-Energy Collision of Quarks and Mesons in the Schwinger Model: From Tensor Networks to Circuit QED0 aHighEnergy Collision of Quarks and Mesons in the Schwinger Model c2/28/20240 v1323 a

With the aim of studying nonperturbative out-of-equilibrium dynamics of high-energy particle collisions on quantum simulators, we investigate the scattering dynamics of lattice quantum electrodynamics in 1+1 dimensions. Working in the bosonized formulation of the model and in the thermodynamic limit, we use uniform-matrix-product-state tensor networks to construct multi-particle wave-packet states, evolve them in time, and detect outgoing particles post collision. This facilitates the numerical simulation of scattering experiments in both confined and deconfined regimes of the model at different energies, giving rise to rich phenomenology, including inelastic production of quark and meson states, meson disintegration, and dynamical string formation and breaking. We obtain elastic and inelastic scattering cross sections, together with time-resolved momentum and position distributions of the outgoing particles. Furthermore, we propose an analog circuit-QED implementation of the scattering process that is native to the platform, requires minimal ingredients and approximations, and enables practical schemes for particle wave-packet preparation and evolution. This study highlights the role of classical and quantum simulation in enhancing our understanding of scattering processes in quantum field theories in real time.

1 aBelyansky, Ron1 aWhitsitt, Seth1 aMueller, Niklas1 aFahimniya, Ali1 aBennewitz, Elizabeth, R.1 aDavoudi, Zohreh1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2307.0252201404nas a2200205 4500008004100000022001400041245010400055210006900159260001400228490000700242520076300249100002401012700002401036700001601060700001701076700002101093700002301114700002401137856003701161 2024 eng d a1089-762300aIon trap with in-vacuum high numerical aperture imaging for a dual-species modular quantum computer0 aIon trap with invacuum high numerical aperture imaging for a dua c3/26/20240 v953 a

Photonic interconnects between quantum systems will play a central role in both scalable quantum computing and quantum networking. Entanglement of remote qubits via photons has been demonstrated in many platforms; however, improving the rate of entanglement generation will be instrumental for integrating photonic links into modular quantum computers. We present an ion trap system that has the highest reported free-space photon collection efficiency for quantum networking. We use a pair of in-vacuum aspheric lenses, each with a numerical aperture of 0.8, to couple 10% of the 493 nm photons emitted from a 138Ba+ ion into single-mode fibers. We also demonstrate that proximal effects of the lenses on the ion position and motion can be mitigated.

1 aCarter, Allison, L.1 aO’Reilly, Jameson1 aToh, George1 aSaha, Sagnik1 aShalaev, Mikhail1 aGoetting, Isabella1 aMonroe, Christopher uhttps://arxiv.org/abs/2310.0705801965nas a2200205 4500008004100000245009400041210006900135260001400204520132100218100002001539700002101559700001701580700002301597700001701620700001801637700001801655700002501673700002401698856003701722 2024 eng d00aLong-Distance Nuclear Matrix Elements for Neutrinoless Double-Beta Decay from Lattice QCD0 aLongDistance Nuclear Matrix Elements for Neutrinoless DoubleBeta c2/14/20243 a

Neutrinoless double-beta (0νββ) decay is a heretofore unobserved process which, if observed, would imply that neutrinos are Majorana particles. Interpretations of the stringent experimental constraints on 0νββ-decay half-lives require calculations of nuclear matrix elements. This work presents the first lattice quantum-chromodynamics (LQCD) calculation of the matrix element for 0νββ decay in a multi-nucleon system, specifically the nn→ppee transition, mediated by a light left-handed Majorana neutrino propagating over nuclear-scale distances. This calculation is performed with quark masses corresponding to a pion mass of mπ=806 MeV at a single lattice spacing and volume. The statistically cleaner Σ−→Σ+ee transition is also computed in order to investigate various systematic uncertainties. The prospects for matching the results of LQCD calculations onto a nuclear effective field theory to determine a leading-order low-energy constant relevant for 0νββ decay with a light Majorana neutrino are investigated. This work, therefore, sets the stage for future calculations at physical values of the quark masses that, combined with effective field theory and nuclear many-body studies, will provide controlled theoretical inputs to experimental searches of 0νββ decay.

1 aDavoudi, Zohreh1 aDetmold, William1 aFu, Zhenghao1 aGrebe, Anthony, V.1 aJay, William1 aMurphy, David1 aOare, Patrick1 aShanahan, Phiala, E.1 aWagman, Michael, L. uhttps://arxiv.org/abs/2402.0936201467nas a2200193 4500008004100000245005900041210005900100260001400159520089600173100002101069700003001090700001901120700001801139700001601157700002401173700001801197700002101215856003701236 2024 eng d00aPhase transition in magic with random quantum circuits0 aPhase transition in magic with random quantum circuits c4/11/20243 a

Magic is a property of quantum states that enables universal fault-tolerant quantum computing using simple sets of gate operations. Understanding the mechanisms by which magic is created or destroyed is, therefore, a crucial step towards efficient and practical fault-tolerant computation. We observe that a random stabilizer code subject to coherent errors exhibits a phase transition in magic, which we characterize through analytic, numeric and experimental probes. Below a critical error rate, stabilizer syndrome measurements remove the accumulated magic in the circuit, effectively protecting against coherent errors; above the critical error rate syndrome measurements concentrate magic. A better understanding of such rich behavior in the resource theory of magic could shed more light on origins of quantum speedup and pave pathways for more efficient magic state generation.

1 aNiroula, Pradeep1 aWhite, Christopher, David1 aWang, Qingfeng1 aJohri, Sonika1 aZhu, Daiwei1 aMonroe, Christopher1 aNoel, Crystal1 aGullans, Michael uhttps://arxiv.org/abs/2304.1048101252nas a2200145 4500008004100000245007000041210006900111260001300180300001100193490000700204520079900211100001601010700001801026856006201044 2024 eng d00aPost-quantum cryptography and the quantum future of cybersecurity0 aPostquantum cryptography and the quantum future of cybersecurity c4/9/2024 a0405010 v213 a

We review the current status of efforts to develop and deploy post-quantum cryptography on the Internet. Then we suggest specific ways in which quantum technologies might be used to enhance cybersecurity in the near future and beyond. We focus on two goals: protecting the secret keys that are used in classical cryptography, and ensuring the trustworthiness of quantum computations. These goals may soon be within reach, thanks to recent progress in both theory and experiment. This progress includes interactive protocols for testing quantumness as well as for performing uncloneable cryptographic computations; and experimental demonstrations of device-independent random number generators, device-independent quantum key distribution, quantum memories, and analog quantum simulators.

1 aLiu, Yi-Kai1 aMoody, Dustin uhttps://link.aps.org/doi/10.1103/PhysRevApplied.21.04050102067nas a2200169 4500008004100000245008100041210006900122260001300191520151900204100002001723700002701743700002001770700002301790700001901813700002801832856003701860 2024 eng d00aQuantum thermodynamics of nonequilibrium processes in lattice gauge theories0 aQuantum thermodynamics of nonequilibrium processes in lattice ga c4/3/20243 a

A key objective in nuclear and high-energy physics is to describe nonequilibrium dynamics of matter, e.g., in the early universe and in particle colliders, starting from the Standard Model. Classical-computing methods, via the framework of lattice gauge theory, have experienced limited success in this mission. Quantum simulation of lattice gauge theories holds promise for overcoming computational limitations. Because of local constraints (Gauss's laws), lattice gauge theories have an intricate Hilbert-space structure. This structure complicates the definition of thermodynamic properties of systems coupled to reservoirs during equilibrium and nonequilibrium processes. We show how to define thermodynamic quantities such as work and heat using strong-coupling thermodynamics, a framework that has recently burgeoned within the field of quantum thermodynamics. Our definitions suit instantaneous quenches, simple nonequilibrium processes undertaken in quantum simulators. To illustrate our framework, we compute the work and heat exchanged during a quench in a Z2 lattice gauge theory coupled to matter in 1+1 dimensions. The thermodynamic quantities, as functions of the quench parameter, evidence an expected phase transition. For general thermal states, we derive a simple relation between a quantum many-body system's entanglement Hamiltonian, measurable with quantum-information-processing tools, and the Hamiltonian of mean force, used to define strong-coupling thermodynamic quantities.

1 aDavoudi, Zohreh1 aJarzynski, Christopher1 aMueller, Niklas1 aOruganti, Greeshma1 aPowers, Connor1 aHalpern, Nicole, Yunger uhttps://arxiv.org/abs/2404.0296501538nas a2200169 4500008004100000022001400041245006400055210006400119260001400183300000900197490000600206520105300212100002201265700002401287700002001311856003701331 2024 eng d a2521-327X00aRandomized measurement protocols for lattice gauge theories0 aRandomized measurement protocols for lattice gauge theories c3/20/2024 a13000 v83 a

Randomized measurement protocols, including classical shadows, entanglement tomography, and randomized benchmarking are powerful techniques to estimate observables, perform state tomography, or extract the entanglement properties of quantum states. While unraveling the intricate structure of quantum states is generally difficult and resource-intensive, quantum systems in nature are often tightly constrained by symmetries. This can be leveraged by the symmetry-conscious randomized measurement schemes we propose, yielding clear advantages over symmetry-blind randomization such as reducing measurement costs, enabling symmetry-based error mitigation in experiments, allowing differentiated measurement of (lattice) gauge theory entanglement structure, and, potentially, the verification of topologically ordered states in existing and near-term experiments. Crucially, unlike symmetry-blind randomized measurement protocols, these latter tasks can be performed without relearning symmetries via full reconstruction of the density matrix.

1 aBringewatt, Jacob1 aKunjummen, Jonathan1 aMueller, Niklas uhttps://arxiv.org/abs/2303.1551902266nas a2200265 4500008004100000245005900041210005900100260001400159520150200173100002901675700001801704700002501722700002001747700002501767700001901792700002001811700001201831700001601843700002201859700001301881700002401894700002001918700002501938856003701963 2024 eng d00aSimulating Meson Scattering on Spin Quantum Simulators0 aSimulating Meson Scattering on Spin Quantum Simulators c3/11/20243 a

Studying high-energy collisions of composite particles, such as hadrons and nuclei, is an outstanding goal for quantum simulators. However, preparation of hadronic wave packets has posed a significant challenge, due to the complexity of hadrons and the precise structure of wave packets. This has limited demonstrations of hadron scattering on quantum simulators to date. Observations of confinement and composite excitations in quantum spin systems have opened up the possibility to explore scattering dynamics in spin models. In this article, we develop two methods to create entangled spin states corresponding to wave packets of composite particles in analog quantum simulators of Ising spin Hamiltonians. One wave-packet preparation method uses the blockade effect enabled by beyond-nearest-neighbor Ising spin interactions. The other method utilizes a quantum-bus-mediated exchange, such as the native spin-phonon coupling in trapped-ion arrays. With a focus on trapped-ion simulators, we numerically benchmark both methods and show that high-fidelity wave packets can be achieved in near-term experiments. We numerically study scattering of wave packets for experimentally realizable parameters in the Ising model and find inelastic-scattering regimes, corresponding to particle production in the scattering event, with prominent and distinct experimental signals. Our proposal, therefore, demonstrates the potential of observing inelastic scattering in near-term quantum simulators.

1 aBennewitz, Elizabeth, R.1 aWare, Brayden1 aSchuckert, Alexander1 aLerose, Alessio1 aSurace, Federica, M.1 aBelyansky, Ron1 aMorong, William1 aLuo, De1 aDe, Arinjoy1 aCollins, Kate, S.1 aKatz, Or1 aMonroe, Christopher1 aDavoudi, Zohreh1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2403.0706102465nas a2200517 4500008004100000245011600041210006900157260001400226520098200240100001701222700001701239700002501256700002001281700002401301700002201325700001601347700001901363700001901382700001801401700001901419700002001438700001901458700002101477700003101498700001801529700001901547700001601566700001601582700001601598700002001614700001901634700002101653700001901674700002201693700001801715700002401733700002301757700001801780700002001798700001801818700002301836700001901859700002001878700001201898856003701910 2023 eng d00aAccelerating Progress Towards Practical Quantum Advantage: The Quantum Technology Demonstration Project Roadmap0 aAccelerating Progress Towards Practical Quantum Advantage The Qu c3/20/20233 a

Quantum information science and technology (QIST) is a critical and emerging technology with the potential for enormous world impact and is currently invested in by over 40 nations. To bring these large-scale investments to fruition and bridge the lower technology readiness levels (TRLs) of fundamental research at universities to the high TRLs necessary to realize the promise of practical quantum advantage accessible to industry and the public, we present a roadmap for Quantum Technology Demonstration Projects (QTDPs). Such QTDPs, focused on intermediate TRLs, are large-scale public-private partnerships with a high probability of translation from laboratory to practice. They create technology demonstrating a clear 'quantum advantage' for science breakthroughs that are user-motivated and will provide access to a broad and diverse community of scientific users. Successful implementation of a program of QTDPs will have large positive economic impacts.

1 aAlsing, Paul1 aBattle, Phil1 aBienfang, Joshua, C.1 aBorders, Tammie1 aBrower-Thomas, Tina1 aCarr, Lincoln, D.1 aChong, Fred1 aDadras, Siamak1 aDeMarco, Brian1 aDeutsch, Ivan1 aFigueroa, Eden1 aFreedman, Danna1 aEveritt, Henry1 aGauthier, Daniel1 aJohnston-Halperin, Ezekiel1 aKim, Jungsang1 aKira, Mackillo1 aKumar, Prem1 aKwiat, Paul1 aLekki, John1 aLoiacono, Anjul1 aLončar, Marko1 aLowell, John, R.1 aLukin, Mikhail1 aMerzbacher, Celia1 aMiller, Aaron1 aMonroe, Christopher1 aPollanen, Johannes1 aPappas, David1 aRaymer, Michael1 aReano, Ronald1 aRodenburg, Brandon1 aSavage, Martin1 aSearles, Thomas1 aYe, Jun uhttps://arxiv.org/abs/2210.1475702420nas a2200157 4500008004100000245006400041210006400105260001500169520193300184100001702117700002802134700002502162700001602187700002202203856003702225 2023 eng d00aAccurate and Honest Approximation of Correlated Qubit Noise0 aAccurate and Honest Approximation of Correlated Qubit Noise c11/15/20233 a

Accurate modeling of noise in realistic quantum processors is critical for constructing fault-tolerant quantum computers. While a full simulation of actual noisy quantum circuits provides information about correlated noise among all qubits and is therefore accurate, it is, however, computationally expensive as it requires resources that grow exponentially with the number of qubits. In this paper, we propose an efficient systematic construction of approximate noise channels, where their accuracy can be enhanced by incorporating noise components with higher qubit-qubit correlation degree. To formulate such approximate channels, we first present a method, dubbed the cluster expansion approach, to decompose the Lindbladian generator of an actual Markovian noise channel into components based on interqubit correlation degree. We then generate a k-th order approximate noise channel by truncating the cluster expansion and incorporating noise components with correlations up to the k-th degree. We require that the approximate noise channels must be accurate and also "honest", i.e., the actual errors are not underestimated in our physical models. As an example application, we apply our method to model noise in a three-qubit quantum processor that stabilizes a [[2,0,0]] codeword, which is one of the four Bell states. We find that, for realistic noise strength typical for fixed-frequency superconducting qubits coupled via always-on static interactions, correlated noise beyond two-qubit correlation can significantly affect the code simulation accuracy. Since our approach provides a systematic noise characterization, it enables the potential for accurate, honest and scalable approximation to simulate large numbers of qubits from full modeling or experimental characterizations of small enough quantum subsystems, which are efficient but still retain essential noise features of the entire device.

1 aSetiawan, F.1 aGramolin, Alexander, V.1 aMatekole, Elisha, S.1 aKrovi, Hari1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2311.0930501210nas a2200157 4500008004100000245004000041210003900081260001400120520077300134100002300907700001900930700002300949700002100972700002200993856003701015 2023 eng d00aCollision-resolved pressure sensing0 aCollisionresolved pressure sensing c3/17/20233 a

Heat and pressure are ultimately transmitted via quantized degrees of freedom, like gas particles and phonons. While a continuous Brownian description of these noise sources is adequate to model measurements with relatively long integration times, sufficiently precise measurements can resolve the detailed time dependence coming from individual bath-system interactions. We propose the use of nanomechanical devices operated with impulse readout sensitivity around the ``standard quantum limit'' to sense ultra-low gas pressures by directly counting the individual collisions of gas particles on a sensor. We illustrate this in two paradigmatic model systems: an optically levitated nanobead and a tethered membrane system in a phononic bandgap shield.

1 aBarker, Daniel, S.1 aCarney, Daniel1 aLeBrun, Thomas, W.1 aMoore, David, C.1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2303.0992201851nas a2200169 4500008004100000245006100041210006000102260001400162520134300176100002501519700001901544700002401563700001801587700001901605700002001624856003701644 2023 eng d00aColloquium: Quantum and Classical Discrete Time Crystals0 aColloquium Quantum and Classical Discrete Time Crystals c5/15/20233 a

The spontaneous breaking of time translation symmetry has led to the discovery of a new phase of matter - the discrete time crystal. Discrete time crystals exhibit rigid subharmonic oscillations, which result from a combination of many-body interactions, collective synchronization, and ergodicity breaking. This Colloquium reviews recent theoretical and experimental advances in the study of quantum and classical discrete time crystals. We focus on the breaking of ergodicity as the key to discrete time crystals and the delaying of ergodicity as the source of numerous phenomena that share many of the properties of discrete time crystals, including the AC Josephson effect, coupled map lattices, and Faraday waves. Theoretically, there exists a diverse array of strategies to stabilize time crystalline order in both closed and open systems, ranging from localization and prethermalization to dissipation and error correction. Experimentally, many-body quantum simulators provide a natural platform for investigating signatures of time crystalline order; recent work utilizing trapped ions, solid-state spin systems, and superconducting qubits will be reviewed. Finally, this Colloquium concludes by describing outstanding challenges in the field and a vision for new directions on both the experimental and theoretical fronts.

1 aZaletel, Michael, P.1 aLukin, Mikhail1 aMonroe, Christopher1 aNayak, Chetan1 aWilczek, Frank1 aYao, Norman, Y. uhttps://arxiv.org/abs/2305.0890402370nas a2200145 4500008004100000245008400041210006900125260001500194520190500209100002102114700001602135700001802151700001802169856003702187 2023 eng d00aCompressed gate characterization for quantum devices with time-correlated noise0 aCompressed gate characterization for quantum devices with timeco c12/22/20233 a

As quantum devices make steady progress towards intermediate scale and fault-tolerant quantum computing, it is essential to develop rigorous and efficient measurement protocols that account for known sources of noise. Most existing quantum characterization protocols such as gate set tomography and randomized benchmarking assume the noise acting on the qubits is Markovian. However, this assumption is often not valid, as for the case of 1/f charge noise or hyperfine nuclear spin noise. Here, we present a general framework for quantum process tomography (QPT) in the presence of time-correlated noise. We further introduce fidelity benchmarks that quantify the relative strength of different sources of Markovian and non-Markovian noise. As an application of our method, we perform a comparative theoretical and experimental analysis of silicon spin qubits. We first develop a detailed noise model that accounts for the dominant sources of noise and validate the model against experimental data. Applying our framework for time-correlated QPT, we find that the number of independent parameters needed to characterize one and two-qubit gates can be compressed by 10x and 100x, respectively, when compared to the fully generic case. These compressions reduce the amount of tomographic measurements needed in experiment, while also significantly speeding up numerical simulations of noisy quantum circuit dynamics compared to time-dependent Hamiltonian simulation. Using this compressed noise model, we find good agreement between our theoretically predicted process fidelities and two qubit interleaved randomized benchmarking fidelities of 99.8% measured in recent experiments on silicon spin qubits. More broadly, our formalism can be directly extended to develop efficient and scalable tuning protocols for high-fidelity control of large-arrays of quantum devices with non-Markovian noise.

1 aGullans, Michael1 aCaranti, M.1 aMills, A., R.1 aPetta, J., R. uhttps://arxiv.org/abs/2307.1443201495nas a2200181 4500008004100000245008500041210006900126260001400195490000800209520092100217100001901138700002101157700002701178700002301205700002001228700002801248856003701276 2023 eng d00aCritical phase and spin sharpening in SU(2)-symmetric monitored quantum circuits0 aCritical phase and spin sharpening in SU2symmetric monitored qua c8/17/20230 v1083 a

Monitored quantum circuits exhibit entanglement transitions at certain measurement rates. Such a transition separates phases characterized by how much information an observer can learn from the measurement outcomes. We study SU(2)-symmetric monitored quantum circuits, using exact numerics and a mapping onto an effective statistical-mechanics model. Due to the symmetry's non-Abelian nature, measuring qubit pairs allows for nontrivial entanglement scaling even in the measurement-only limit. We find a transition between a volume-law entangled phase and a critical phase whose diffusive purification dynamics emerge from the non-Abelian symmetry. Additionally, we numerically identify a "spin-sharpening transition." On one side is a phase in which the measurements can efficiently identify the system's total spin quantum number; on the other side is a phase in which measurements cannot.

1 aMajidy, Shayan1 aAgrawal, Utkarsh1 aGopalakrishnan, Sarang1 aPotter, Andrew, C.1 aVasseur, Romain1 aHalpern, Nicole, Yunger uhttps://arxiv.org/abs/2305.1335601846nas a2200337 4500008004100000245008100041210006900122260001500191520083900206100002401045700002201069700001801091700001801109700002001127700002301147700002301170700002301193700002301216700002301239700002101262700001801283700002201301700002401323700001701347700002501364700002101389700002301410700002101433700001701454856003701471 2023 eng d00aData Needs and Challenges of Quantum Dot Devices Automation: Workshop Report0 aData Needs and Challenges of Quantum Dot Devices Automation Work c12/21/20233 a

Gate-defined quantum dots are a promising candidate system to realize scalable, coupled qubit systems and serve as a fundamental building block for quantum computers. However, present-day quantum dot devices suffer from imperfections that must be accounted for, which hinders the characterization, tuning, and operation process. Moreover, with an increasing number of quantum dot qubits, the relevant parameter space grows sufficiently to make heuristic control infeasible. Thus, it is imperative that reliable and scalable autonomous tuning approaches are developed. In this report, we outline current challenges in automating quantum dot device tuning and operation with a particular focus on datasets, benchmarking, and standardization. We also present ideas put forward by the quantum dot community on how to overcome them.

1 aZwolak, Justyna, P.1 aTaylor, Jacob, M.1 aAndrews, Reed1 aBenson, Jared1 aBryant, Garnett1 aButerakos, Donovan1 aChatterjee, Anasua1 aSarma, Sankar, Das1 aEriksson, Mark, A.1 aGreplová, Eliška1 aGullans, Michael1 aHader, Fabian1 aKovach, Tyler, J.1 aMundada, Pranav, S.1 aRamsey, Mick1 aRasmussen, Torbjoern1 aSeverin, Brandon1 aSigillito, Anthony1 aUndseth, Brennan1 aWeber, Brian uhttps://arxiv.org/abs/2312.1432201726nas a2200253 4500008004100000022001400041245005000055210005000105260001500155490000600170520104100176100002201217700002201239700001801261700002101279700001601300700001301316700002901329700001801358700002401376700001901400700001601419856003701435 2023 eng d a2375-254800aDigital quantum simulation of NMR experiments0 aDigital quantum simulation of NMR experiments c11/29/20230 v93 a

Simulations of nuclear magnetic resonance (NMR) experiments can be an important tool for extracting information about molecular structure and optimizing experimental protocols but are often intractable on classical computers for large molecules such as proteins and for protocols such as zero-field NMR. We demonstrate the first quantum simulation of an NMR spectrum, computing the zero-field spectrum of the methyl group of acetonitrile using four qubits of a trapped-ion quantum computer. We reduce the sampling cost of the quantum simulation by an order of magnitude using compressed sensing techniques. We show how the intrinsic decoherence of NMR systems may enable the zero-field simulation of classically hard molecules on relatively near-term quantum hardware and discuss how the experimentally demonstrated quantum algorithm can be used to efficiently simulate scientifically and technologically relevant solid-state NMR experiments on more mature devices. Our work opens a practical application for quantum computation.

1 aSeetharam, Kushal1 aBiswas, Debopriyo1 aNoel, Crystal1 aRisinger, Andrew1 aZhu, Daiwei1 aKatz, Or1 aChattopadhyay, Sambuddha1 aCetina, Marko1 aMonroe, Christopher1 aDemler, Eugene1 aSels, Dries uhttps://arxiv.org/abs/2109.1329802172nas a2200133 4500008004100000245008500041210006900126260001500195520173200210100002401942700001701966700001801983856003702001 2023 eng d00aEvaluating the security of CRYSTALS-Dilithium in the quantum random oracle model0 aEvaluating the security of CRYSTALSDilithium in the quantum rand c12/17/20233 a

In the wake of recent progress on quantum computing hardware, the National Institute of Standards and Technology (NIST) is standardizing cryptographic protocols that are resistant to attacks by quantum adversaries. The primary digital signature scheme that NIST has chosen is CRYSTALS-Dilithium. The hardness of this scheme is based on the hardness of three computational problems: Module Learning with Errors (MLWE), Module Short Integer Solution (MSIS), and SelfTargetMSIS. MLWE and MSIS have been well-studied and are widely believed to be secure. However, SelfTargetMSIS is novel and, though classically as hard as MSIS, its quantum hardness is unclear. In this paper, we provide the first proof of the hardness of SelfTargetMSIS via a reduction from MLWE in the Quantum Random Oracle Model (QROM). Our proof uses recently developed techniques in quantum reprogramming and rewinding. A central part of our approach is a proof that a certain hash function, derived from the MSIS problem, is collapsing. From this approach, we deduce a new security proof for Dilithium under appropriate parameter settings. Compared to the only other rigorous security proof for a variant of Dilithium, Dilithium-QROM, our proof has the advantage of being applicable under the condition q = 1 mod 2n, where q denotes the modulus and n the dimension of the underlying algebraic ring. This condition is part of the original Dilithium proposal and is crucial for the efficient implementation of the scheme. We provide new secure parameter sets for Dilithium under the condition q = 1 mod 2n, finding that our public key sizes and signature sizes are about 2.5 to 2.8 times larger than those of Dilithium-QROM for the same security levels.

1 aJackson, Kelsey, A.1 aMiller, Carl1 aWang, Daochen uhttps://arxiv.org/abs/2312.1661901229nas a2200157 4500008004100000245007900041210006900120260001300189520074400202100001900946700001700965700001300982700002100995700001801016856003701034 2023 eng d00aEver more optimized simulations of fermionic systems on a quantum computer0 aEver more optimized simulations of fermionic systems on a quantu c3/6/20233 a

Despite using a novel model of computation, quantum computers break down programs into elementary gates. Among such gates, entangling gates are the most expensive. In the context of fermionic simulations, we develop a suite of compilation and optimization techniques that massively reduce the entangling-gate counts. We exploit the well-studied non-quantum optimization algorithms to achieve up to 24\% savings over the state of the art for several small-molecule simulations, with no loss of accuracy or hidden costs. Our methodologies straightforwardly generalize to wider classes of near-term simulations of the ground state of a fermionic system or real-time simulations probing dynamical properties of a fermionic system. 

1 aWang, Qingfeng1 aCian, Ze-Pei1 aLi, Ming1 aMarkov, Igor, L.1 aNam, Yunseong uhttps://arxiv.org/abs/2303.0346002121nas a2200181 4500008004100000245006900041210006800110260001400178520156100192100001901753700002201772700001901794700001901813700002401832700002501856700002101881856003701902 2023 eng d00aFault-tolerant hyperbolic Floquet quantum error correcting codes0 aFaulttolerant hyperbolic Floquet quantum error correcting codes c9/18/20233 a

A central goal in quantum error correction is to reduce the overhead of fault-tolerant quantum computing by increasing noise thresholds and reducing the number of physical qubits required to sustain a logical qubit. We introduce a potential path towards this goal based on a family of dynamically generated quantum error correcting codes that we call "hyperbolic Floquet codes." These codes are defined by a specific sequence of non-commuting two-body measurements arranged periodically in time that stabilize a topological code on a hyperbolic manifold with negative curvature. We focus on a family of lattices for n qubits that, according to our prescription that defines the code, provably achieve a finite encoding rate (1/8+2/n) and have a depth-3 syndrome extraction circuit. Similar to hyperbolic surface codes, the distance of the code at each time-step scales at most logarithmically in n. The family of lattices we choose indicates that this scaling is achievable in practice. We develop and benchmark an efficient matching-based decoder that provides evidence of a threshold near 0.1% in a phenomenological noise model. Utilizing weight-two check operators and a qubit connectivity of 3, one of our hyperbolic Floquet codes uses 400 physical qubits to encode 52 logical qubits with a code distance of 8, i.e., it is a [[400,52,8]] code. At small error rates, comparable logical error suppression to this code requires 5x as many physical qubits (1924) when using the honeycomb Floquet code with the same noise model and decoder.

1 aFahimniya, Ali1 aDehghani, Hossein1 aBharti, Kishor1 aMathew, Sheryl1 aKollár, Alicia, J.1 aGorshkov, Alexey, V.1 aGullans, Michael uhttps://arxiv.org/abs/2309.1003301926nas a2200181 4500008004100000245010800041210006900149260001300218520132500231100001901556700001901575700002001594700001901614700002901633700002001662700002501682856003701707 2023 eng d00aHigh-Energy Collision of Quarks and Hadrons in the Schwinger Model: From Tensor Networks to Circuit QED0 aHighEnergy Collision of Quarks and Hadrons in the Schwinger Mode c7/5/20233 a

With the aim of studying nonperturbative out-of-equilibrium dynamics of high-energy particle collisions on quantum simulators, we investigate the scattering dynamics of lattice quantum electrodynamics in 1+1 dimensions. Working in the bosonized formulation of the model, we propose an analog circuit-QED implementation that is native to the platform, requires minimal ingredients and approximations, and enables practical schemes for particle wave-packet preparation and evolution. Furthermore, working in the thermodynamic limit, we use uniform-matrix-product-state tensor networks to construct multi-particle wave-packet states, evolve them in time, and detect outgoing particles post collision. This facilitates the numerical simulation of scattering experiments in both confined and deconfined regimes of the model at different energies, giving rise to rich phenomenology, including inelastic production of quark and meson states, meson disintegration, and dynamical string formation and breaking. We obtain elastic and inelastic scattering cross sections, together with time-resolved momentum and position distributions of the outgoing particles. This study highlights the role of classical and quantum simulation in enhancing our understanding of scattering processes in quantum field theories in real time.

1 aBelyansky, Ron1 aWhitsitt, Seth1 aMueller, Niklas1 aFahimniya, Ali1 aBennewitz, Elizabeth, R.1 aDavoudi, Zohreh1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2307.0252201026nas a2200349 4500008004100000022001400041245006600055210006600121260001400187100002100201700002200222700002400244700001900268700001800287700001800305700001800323700001800341700002300359700002400382700002800406700002000434700001500454700001300469700002800482700002300510700002200533700002100555700002000576700002000596700002300616856003700639 2023 eng d a1476-468700aLogical quantum processor based on reconfigurable atom arrays0 aLogical quantum processor based on reconfigurable atom arrays c12/7/20231 aBluvstein, Dolev1 aEvered, Simon, J.1 aGeim, Alexandra, A.1 aLi, Sophie, H.1 aZhou, Hengyun1 aManovitz, Tom1 aEbadi, Sepehr1 aCain, Madelyn1 aKalinowski, Marcin1 aHangleiter, Dominik1 aAtaides, Pablo, Bonilla1 aMaskara, Nishad1 aCong, Iris1 aGao, Xun1 aRodriguez, Pedro, Sales1 aKarolyshyn, Thomas1 aSemeghini, Giulia1 aGullans, Michael1 aGreiner, Markus1 aVuletic, Vladan1 aLukin, Mikhail, D. uhttps://arxiv.org/abs/2312.0398202618nas a2200229 4500008004100000245007500041210006900116260001500185520193200200100001902132700002002151700002602171700001702197700001802214700001802232700002302250700002202273700001502295700001802310700002302328856003702351 2023 eng d00aMicrowave signal processing using an analog quantum reservoir computer0 aMicrowave signal processing using an analog quantum reservoir co c12/26/20233 a

Quantum reservoir computing (QRC) has been proposed as a paradigm for performing machine learning with quantum processors where the training is efficient in the number of required runs of the quantum processor and takes place in the classical domain, avoiding the issue of barren plateaus in parameterized-circuit quantum neural networks. It is natural to consider using a quantum processor based on superconducting circuits to classify microwave signals that are analog -- continuous in time. However, while theoretical proposals of analog QRC exist, to date QRC has been implemented using circuit-model quantum systems -- imposing a discretization of the incoming signal in time, with each time point input by executing a gate operation. In this paper we show how a quantum superconducting circuit comprising an oscillator coupled to a qubit can be used as an analog quantum reservoir for a variety of classification tasks, achieving high accuracy on all of them. Our quantum system was operated without artificially discretizing the input data, directly taking in microwave signals. Our work does not attempt to address the question of whether QRCs could provide a quantum computational advantage in classifying pre-recorded classical signals. However, beyond illustrating that sophisticated tasks can be performed with a modest-size quantum system and inexpensive training, our work opens up the possibility of achieving a different kind of advantage than a purely computational advantage: superconducting circuits can act as extremely sensitive detectors of microwave photons; our work demonstrates processing of ultra-low-power microwave signals in our superconducting circuit, and by combining sensitive detection with QRC processing within the same system, one could achieve a quantum sensing-computational advantage, i.e., an advantage in the overall analysis of microwave signals comprising just a few photons.

1 aSenanian, Alen1 aPrabhu, Sridhar1 aKremenetski, Vladimir1 aRoy, Saswata1 aCao, Yingkang1 aKline, Jeremy1 aOnodera, Tatsuhiro1 aWright, Logan, G.1 aWu, Xiaodi1 aFatemi, Valla1 aMcMahon, Peter, L. uhttps://arxiv.org/abs/2312.1616602055nas a2200241 4500008004100000245005300041210005200094260001300146490000800159520125800167653002701425653004201452653003901494653003101533653004701564653005201611100002201663700002101685700002201706700002001728700002801748856003701776 2023 eng d00aNon-Abelian eigenstate thermalization hypothesis0 aNonAbelian eigenstate thermalization hypothesis c4/6/20230 v1303 a

The eigenstate thermalization hypothesis (ETH) explains why chaotic quantum many-body systems thermalize internally if the Hamiltonian lacks symmetries. If the Hamiltonian conserves one quantity ("charge"), the ETH implies thermalization within a charge sector -- in a microcanonical subspace. But quantum systems can have charges that fail to commute with each other and so share no eigenbasis; microcanonical subspaces may not exist. Furthermore, the Hamiltonian will have degeneracies, so the ETH need not imply thermalization. We adapt the ETH to noncommuting charges by positing a non-Abelian ETH and invoking the approximate microcanonical subspace introduced in quantum thermodynamics. Illustrating with SU(2) symmetry, we apply the non-Abelian ETH in calculating local observables' time-averaged and thermal expectation values. In many cases, we prove, the time average thermalizes. However, we also find cases in which, under a physically reasonable assumption, the time average converges to the thermal average unusually slowly as a function of the global-system size. This work extends the ETH, a cornerstone of many-body physics, to noncommuting charges, recently a subject of intense activity in quantum thermodynamics.

10aFOS: Physical sciences10aHigh Energy Physics - Theory (hep-th)10aQuantum Gases (cond-mat.quant-gas)10aQuantum Physics (quant-ph)10aStatistical Mechanics (cond-mat.stat-mech)10aStrongly Correlated Electrons (cond-mat.str-el)1 aMurthy, Chaitanya1 aBabakhani, Arman1 aIniguez, Fernando1 aSrednicki, Mark1 aHalpern, Nicole, Yunger uhttps://arxiv.org/abs/2206.0531001491nas a2200157 4500008004100000245005900041210005800100260001300158490000800171520102800179100001901207700002201226700002001248700002801268856003701296 2023 eng d00aNon-Abelian symmetry can increase entanglement entropy0 aNonAbelian symmetry can increase entanglement entropy c1/3/20230 v1073 a

The pillars of quantum theory include entanglement and operators' failure to commute. The Page curve quantifies the bipartite entanglement of a many-body system in a random pure state. This entanglement is known to decrease if one constrains extensive observables that commute with each other (Abelian ``charges''). Non-Abelian charges, which fail to commute with each other, are of current interest in quantum thermodynamics. For example, noncommuting charges were shown to reduce entropy-production rates and may enhance finite-size deviations from eigenstate thermalization. Bridging quantum thermodynamics to many-body physics, we quantify the effects of charges' noncommutation -- of a symmetry's non-Abelian nature -- on Page curves. First, we construct two models that are closely analogous but differ in whether their charges commute. We show analytically and numerically that the noncommuting-charge case has more entanglement. Hence charges' noncommutation can promote entanglement.

1 aMajidy, Shayan1 aLasek, Aleksander1 aHuse, David, A.1 aHalpern, Nicole, Yunger uhttps://arxiv.org/abs/2209.1430301843nas a2200157 4500008004100000245011500041210006900156260001500225300001100240490000800251520127800259100003501537700002501572700002801597856006001625 2023 eng d00aNonclassical Advantage in Metrology Established via Quantum Simulations of Hypothetical Closed Timelike Curves0 aNonclassical Advantage in Metrology Established via Quantum Simu c10/12/2023 a1502020 v1313 a

We construct a metrology experiment in which the metrologist can sometimes amend the input state by simulating a closed timelike curve, a worldline that travels backward in time. The existence of closed timelike curves is hypothetical. Nevertheless, they can be simulated probabilistically by quantum-teleportation circuits. We leverage such simulations to pinpoint a counterintuitive nonclassical advantage achievable with entanglement. Our experiment echoes a common information-processing task: A metrologist must prepare probes to input into an unknown quantum interaction. The goal is to infer as much information per probe as possible. If the input is optimal, the information gained per probe can exceed any value achievable classically. The problem is that, only after the interaction does the metrologist learn which input would have been optimal. The metrologist can attempt to change the input by effectively teleporting the optimal input back in time, via entanglement manipulation. The effective time travel sometimes fails but ensures that, summed over trials, the metrologist’s winnings are positive. Our Gedankenexperiment demonstrates that entanglement can generate operational advantages forbidden in classical chronology-respecting theories.

1 aArvidsson-Shukur, David, R. M.1 aMcConnell, Aidan, G.1 aHalpern, Nicole, Yunger uhttps://link.aps.org/doi/10.1103/PhysRevLett.131.15020201518nas a2200169 4500008004100000245007200041210006900113260001300182520098500195100001901180700002501199700002201224700002101246700001601267700002801283856003701311 2023 eng d00aNoncommuting conserved charges in quantum thermodynamics and beyond0 aNoncommuting conserved charges in quantum thermodynamics and bey c9/7/20233 a

Thermodynamic systems typically conserve quantities ("charges") such as energy and particle number. The charges are often assumed implicitly to commute with each other. Yet quantum phenomena such as uncertainty relations rely on observables' failure to commute. How do noncommuting charges affect thermodynamic phenomena? This question, upon arising at the intersection of quantum information theory and thermodynamics, spread recently across many-body physics. Charges' noncommutation has been found to invalidate derivations of the thermal state's form, decrease entropy production, conflict with the eigenstate thermalization hypothesis, and more. This Perspective surveys key results in, opportunities for, and work adjacent to the quantum thermodynamics of noncommuting charges. Open problems include a conceptual puzzle: Evidence suggests that noncommuting charges may hinder thermalization in some ways while enhancing thermalization in others.

1 aMajidy, Shayan1 aBraasch, William, F.1 aLasek, Aleksander1 aUpadhyaya, Twesh1 aKalev, Amir1 aHalpern, Nicole, Yunger uhttps://arxiv.org/abs/2306.0005401834nas a2200217 4500008004100000245007700041210006900118260001400187520122500201100001101426700001301437700001601450700001501466700001201481700001401493700001501507700002501522700001701547700001501564856003701579 2023 eng d00aNon-equilibrium critical scaling and universality in a quantum simulator0 aNonequilibrium critical scaling and universality in a quantum si c9/19/20233 a

Universality and scaling laws are hallmarks of equilibrium phase transitions and critical phenomena. However, extending these concepts to non-equilibrium systems is an outstanding challenge. Despite recent progress in the study of dynamical phases, the universality classes and scaling laws for non-equilibrium phenomena are far less understood than those in equilibrium. In this work, using a trapped-ion quantum simulator with single-ion resolution, we investigate the non-equilibrium nature of critical fluctuations following a quantum quench to the critical point. We probe the scaling of spin fluctuations after a series of quenches to the critical Hamiltonian of a long-range Ising model. With systems of up to 50 spins, we show that the amplitude and timescale of the post-quench fluctuations scale with system size with distinct universal critical exponents. While a generic quench can lead to thermal critical behaviour, we find that a second quench from one critical state to another (i.e. a double quench) results in critical behaviour that does not have an equilibrium counterpart. Our results demonstrate the ability of quantum simulators to explore universal scaling beyond the equilibrium paradigm.

1 aDe, A.1 aCook, P.1 aCollins, K.1 aMorong, W.1 aPaz, D.1 aTitum, P.1 aPagano, G.1 aGorshkov, Alexey, V.1 aMaghrebi, M.1 aMonroe, C. uhttps://arxiv.org/abs/2309.1085602080nas a2200193 4500008004100000245009100041210006900132260001500201520147600216100002501692700001301717700001401730700001901744700001601763700002101779700002501800700002401825856003701849 2023 eng d00aObservation of a finite-energy phase transition in a one-dimensional quantum simulator0 aObservation of a finiteenergy phase transition in a onedimension c10/30/20233 a

One of the most striking many-body phenomena in nature is the sudden change of macroscopic properties as the temperature or energy reaches a critical value. Such equilibrium transitions have been predicted and observed in two and three spatial dimensions, but have long been thought not to exist in one-dimensional (1D) systems. Fifty years ago, Dyson and Thouless pointed out that a phase transition in 1D can occur in the presence of long-range interactions, but an experimental realization has so far not been achieved due to the requirement to both prepare equilibrium states and realize sufficiently long-range interactions. Here we report on the first experimental demonstration of a finite-energy phase transition in 1D. We use the simple observation that finite-energy states can be prepared by time-evolving product initial states and letting them thermalize under the dynamics of a many-body Hamiltonian. By preparing initial states with different energies in a 1D trapped-ion quantum simulator, we study the finite-energy phase diagram of a long-range interacting quantum system. We observe a ferromagnetic equilibrium phase transition as well as a crossover from a low-energy polarized paramagnet to a high-energy unpolarized paramagnet in a system of up to 23 spins, in excellent agreement with numerical simulations. Our work demonstrates the ability of quantum simulators to realize and study previously inaccessible phases at finite energy density.

1 aSchuckert, Alexander1 aKatz, Or1 aFeng, Lei1 aCrane, Eleanor1 aDe, Arinjoy1 aHafezi, Mohammad1 aGorshkov, Alexey, V.1 aMonroe, Christopher uhttps://arxiv.org/abs/2310.1986901855nas a2200145 4500008004100000245007300041210006900114260001500183520138800198100002201586700001901608700002001627700002501647856003701672 2023 eng d00aProjective toric designs, difference sets, and quantum state designs0 aProjective toric designs difference sets and quantum state desig c11/22/20233 a

Trigonometric cubature rules of degree t are sets of points on the torus over which sums reproduce integrals of degree t monomials over the full torus. They can be thought of as t-designs on the torus. Motivated by the projective structure of quantum mechanics, we develop the notion of t-designs on the projective torus, which, surprisingly, have a much more restricted structure than their counterparts on full tori. We provide various constructions of these projective toric designs and prove some bounds on their size and characterizations of their structure. We draw connections between projective toric designs and a diverse set of mathematical objects, including difference and Sidon sets from the field of additive combinatorics, symmetric, informationally complete positive operator valued measures (SIC-POVMs) and complete sets of mutually unbiased bases (MUBs) (which are conjectured to relate to finite projective geometry) from quantum information theory, and crystal ball sequences of certain root lattices. Using these connections, we prove bounds on the maximal size of dense Btmodm sets. We also use projective toric designs to construct families of quantum state designs. Finally, we discuss many open questions about the properties of these projective toric designs and how they relate to other questions in number theory, geometry, and quantum information.

1 aIosue, Joseph, T.1 aMooney, T., C.1 aEhrenberg, Adam1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2311.1347901916nas a2200169 4500008004100000245011700041210006900158260001400227520133400241100002001575700002001595700002101615700002001636700002701656700002601683856003701709 2023 eng d00aQuantum computation of dynamical quantum phase transitions and entanglement tomography in a lattice gauge theory0 aQuantum computation of dynamical quantum phase transitions and e c10/6/20233 a

Strongly-coupled gauge theories far from equilibrium may exhibit unique features that could illuminate the physics of the early universe and of hadron and ion colliders. Studying real-time phenomena has proven challenging with classical-simulation methods, but is a natural application of quantum simulation. To demonstrate this prospect, we quantum compute non-equal time correlation functions and perform entanglement tomography of non-equilibrium states of a simple lattice gauge theory, the Schwinger model, using a trapped-ion quantum computer by IonQ Inc. As an ideal target for near-term devices, a recently-predicted [Zache et al., Phys. Rev. Lett. 122, 050403 (2019)] dynamical quantum phase transition in this model is studied by preparing, quenching, and tracking the subsequent non-equilibrium dynamics in three ways: i) overlap echos signaling dynamical transitions, ii) non-equal time correlation functions with an underlying topological nature, and iii) the entanglement structure of non-equilibrium states, including entanglement Hamiltonians. These results constitute the first observation of a dynamical quantum phase transition in a lattice gauge theory on a quantum computer, and are a first step toward investigating topological phenomena in nuclear and high-energy physics using quantum technologies.

1 aMueller, Niklas1 aCarolan, Joseph1 aConnelly, Andrew1 aDavoudi, Zohreh1 aDumitrescu, Eugene, F.1 aYeter-Aydeniz, Kübra uhttps://arxiv.org/abs/2210.0308901735nas a2200145 4500008004100000245007200041210006900113260001400182490000800196520127600204100003501480700002501515700002801540856002101568 2023 eng d00aQuantum simulations of time travel can power nonclassical metrology0 aQuantum simulations of time travel can power nonclassical metrol c11/3/20230 v1313 a

We construct a metrology experiment in which the metrologist can sometimes amend her input state by simulating a closed timelike curve, a worldline that travels backward in time. The existence of closed timelike curves is hypothetical. Nevertheless, they can be simulated probabilistically by quantum-teleportation circuits. We leverage such simulations to pinpoint a counterintuitive nonclassical advantage achievable with entanglement. Our experiment echoes a common information-processing task: A metrologist must prepare probes to input into an unknown quantum interaction. The goal is to infer as much information per probe as possible. If the input is optimal, the information gained per probe can exceed any value achievable classically. The problem is that, only after the interaction does the metrologist learn which input would have been optimal. The metrologist can attempt to change her input by effectively teleporting the optimal input back in time, via entanglement manipulation. The effective time travel sometimes fails but ensures that, summed over trials, the metrologist's winnings are positive. Our Gedankenexperiment demonstrates that entanglement can generate operational advantages forbidden in classical chronology-respecting theories.

1 aArvidsson-Shukur, David, R. M.1 aMcConnell, Aidan, G.1 aHalpern, Nicole, Yunger uarXiv:2207.0766605435nas a2201621 4500008004100000245010800041210006900149260001500218520094500233100001801178700002301196700001601219700002801235700002001263700002001283700001601303700002001319700002101339700002401360700001901384700001901403700002601422700001801448700002301466700002101489700001601510700001701526700002101543700002301564700002101587700001601608700001701624700003101641700003401672700001801706700001801724700002101742700001801763700002401781700001801805700002001823700003501843700002201878700001601900700002001916700001901936700001701955700001901972700002301991700001802014700002402032700002302056700002302079700001802102700001702120700001902137700002602156700002002182700001902202700001902221700002302240700001802263700002202281700001802303700001902321700002802340700002402368700001902392700002002411700002002431700002702451700001202478700001702490700001502507700002102522700001802543700001902561700003202580700002402612700002202636700003102658700001702689700002302706700002402729700002002753700001902773700001902792700001602811700001702827700001802844700001802862700002002880700001902900700002302919700001902942700001702961700002602978700001603004700002003020700001603040700001803056700002803074700002103102700001803123700002403141700001403165700002303179700002003202700002103222700002003243700001803263700001803281700002103299700002103320700002303341700001803364700001803382700001403400700001903414700001603433700001503449700002003464700002103484700002103505700001703526700002803543700002203571700002303593700002603616700001503642700001703657700002303674700002403697700001803721700001703739700002003756856003703776 2023 eng d00aQuantum-centric Supercomputing for Materials Science: A Perspective on Challenges and Future Directions0 aQuantumcentric Supercomputing for Materials Science A Perspectiv c12/14/20233 a

Computational models are an essential tool for the design, characterization, and discovery of novel materials. Hard computational tasks in materials science stretch the limits of existing high-performance supercomputing centers, consuming much of their simulation, analysis, and data resources. Quantum computing, on the other hand, is an emerging technology with the potential to accelerate many of the computational tasks needed for materials science. In order to do that, the quantum technology must interact with conventional high-performance computing in several ways: approximate results validation, identification of hard problems, and synergies in quantum-centric supercomputing. In this paper, we provide a perspective on how quantum-centric supercomputing can help address critical computational problems in materials science, the challenges to face in order to solve representative use cases, and new suggested directions.

1 aAlexeev, Yuri1 aAmsler, Maximilian1 aBaity, Paul1 aBarroca, Marco, Antonio1 aBassini, Sanzio1 aBattelle, Torey1 aCamps, Daan1 aCasanova, David1 aChoi, Young, jai1 aChong, Frederic, T.1 aChung, Charles1 aCodella, Chris1 aCorcoles, Antonio, D.1 aCruise, James1 aDi Meglio, Alberto1 aDubois, Jonathan1 aDuran, Ivan1 aEckl, Thomas1 aEconomou, Sophia1 aEidenbenz, Stephan1 aElmegreen, Bruce1 aFare, Clyde1 aFaro, Ismael1 aFernández, Cristina, Sanz1 aFerreira, Rodrigo, Neumann Ba1 aFuji, Keisuke1 aFuller, Bryce1 aGagliardi, Laura1 aGalli, Giulia1 aGlick, Jennifer, R.1 aGobbi, Isacco1 aGokhale, Pranav1 aGonzalez, Salvador, de la Puen1 aGreiner, Johannes1 aGropp, Bill1 aGrossi, Michele1 aGull, Emmanuel1 aHealy, Burns1 aHuang, Benchen1 aHumble, Travis, S.1 aIto, Nobuyasu1 aIzmaylov, Artur, F.1 aJavadi-Abhari, Ali1 aJennewein, Douglas1 aJha, Shantenu1 aJiang, Liang1 aJones, Barbara1 ade Jong, Wibe, Albert1 aJurcevic, Petar1 aKirby, William1 aKister, Stefan1 aKitagawa, Masahiro1 aKlassen, Joel1 aKlymko, Katherine1 aKoh, Kwangwon1 aKondo, Masaaki1 aKurkcuoglu, Doga, Murat1 aKurowski, Krzysztof1 aLaino, Teodoro1 aLandfield, Ryan1 aLeininger, Matt1 aLeyton-Ortega, Vicente1 aLi, Ang1 aLin, Meifeng1 aLiu, Junyu1 aLorente, Nicolas1 aLuckow, Andre1 aMartiel, Simon1 aMartin-Fernandez, Francisco1 aMartonosi, Margaret1 aMarvinney, Claire1 aMedina, Arcesio, Castaneda1 aMerten, Dirk1 aMezzacapo, Antonio1 aMichielsen, Kristel1 aMitra, Abhishek1 aMittal, Tushar1 aMoon, Kyungsun1 aMoore, Joel1 aMotta, Mario1 aNa, Young-Hye1 aNam, Yunseong1 aNarang, Prineha1 aOhnishi, Yu-ya1 aOttaviani, Daniele1 aOtten, Matthew1 aPakin, Scott1 aPascuzzi, Vincent, R.1 aPenault, Ed1 aPiontek, Tomasz1 aPitera, Jed1 aRall, Patrick1 aRavi, Gokul, Subramania1 aRobertson, Niall1 aRossi, Matteo1 aRydlichowski, Piotr1 aRyu, Hoon1 aSamsonidze, Georgy1 aSato, Mitsuhisa1 aSaurabh, Nishant1 aSharma, Vidushi1 aSharma, Kunal1 aShin, Soyoung1 aSlessman, George1 aSteiner, Mathias1 aSitdikov, Iskandar1 aSuh, In-Saeng1 aSwitzer, Eric1 aTang, Wei1 aThompson, Joel1 aTodo, Synge1 aTran, Minh1 aTrenev, Dimitar1 aTrott, Christian1 aTseng, Huan-Hsin1 aTureci, Esin1 aValinas, David, García1 aVallecorsa, Sofia1 aWever, Christopher1 aWojciechowski, Konrad1 aWu, Xiaodi1 aYoo, Shinjae1 aYoshioka, Nobuyuki1 aYu, Victor, Wen-zhe1 aYunoki, Seiji1 aZhuk, Sergiy1 aZubarev, Dmitry uhttps://arxiv.org/abs/2312.0973301491nas a2200181 4500008004100000245008400041210006900125260001400194520089300208100003001101700002701131700003001158700002101188700001801209700002401227700002101251856003701272 2023 eng d00aSpin-selective strong light-matter coupling in a 2D hole gas-microcavity system0 aSpinselective strong lightmatter coupling in a 2D hole gasmicroc c2/12/20233 a

The interplay between time-reversal symmetry breaking and strong light-matter coupling in 2D gases brings intriguing aspects to polariton physics. This combination can lead to polarization/spin selective light-matter interaction in the strong coupling regime. In this work, we report such a selective strong light-matter interaction by harnessing a 2D gas in the quantum Hall regime coupled to a microcavity. Specifically, we demonstrate circular-polarization dependence of the vacuum Rabi splitting, as a function of magnetic field and hole density. We provide a quantitative understanding of the phenomenon by modeling the coupling of optical transitions between Landau levels to the microcavity. This method introduces a control tool over the spin degree of freedom in polaritonic semiconductor systems, paving the way for new experimental possibilities in light-matter hybrids.

1 aSuarez-Forero, Daniel, G.1 aSession, Deric, Weston1 aMehrabad, Mahmoud, Jalali1 aKnuppel, Patrick1 aFaelt, Stefan1 aWegscheider, Werner1 aHafezi, Mohammad uhttps://arxiv.org/abs/2302.0602301752nas a2200133 4500008004100000245009000041210007000131260001400201520130500215100002201520700002001542700001901562856003701581 2023 eng d00aOn the stability of solutions to Schrödinger's equation short of the adiabatic limit0 astability of solutions to Schrödingers equation short of the adi c3/23/20233 a

We prove an adiabatic theorem that applies at timescales short of the adiabatic limit. Our proof analyzes the stability of solutions to Schrodinger's equation under perturbation. We directly characterize cross-subspace effects of perturbation, which are typically significantly less than suggested by the perturbation's operator norm. This stability has numerous consequences: we can (1) find timescales where the solution of Schrodinger's equation converges to the ground state of a block, (2) lower bound the convergence to the global ground state by demonstrating convergence to some other known quantum state, (3) guarantee faster convergence than the standard adiabatic theorem when the ground state of the perturbed Hamiltonian (H) is close to that of the unperturbed H, and (4) bound tunneling effects in terms of the global spectral gap when H is ``stoquastic'' (a Z-matrix). Our results apply to quantum annealing protocols with faster convergence than usually guaranteed by a standard adiabatic theorem. Our upper and lower bounds demonstrate that at timescales short of the adiabatic limit, subspace dynamics can dominate over global dynamics. Thus, we see that convergence to particular target states can be understood as the result of otherwise local dynamics.

1 aBringewatt, Jacob1 aJarret, Michael1 aMooney, T., C. uhttps://arxiv.org/abs/2303.1347802171nas a2200289 4500008004100000245007500041210006900116260001400185520131000199100002201509700002001531700002001551700002401571700002401595700002001619700001901639700002001658700002901678700001801707700002001725700001801745700002301763700001701786700001701803700002401820856003701844 2023 eng d00aVerifiable measurement-based quantum random sampling with trapped ions0 aVerifiable measurementbased quantum random sampling with trapped c7/26/20233 a

Quantum computers are now on the brink of outperforming their classical counterparts. One way to demonstrate the advantage of quantum computation is through quantum random sampling performed on quantum computing devices. However, existing tools for verifying that a quantum device indeed performed the classically intractable sampling task are either impractical or not scalable to the quantum advantage regime. The verification problem thus remains an outstanding challenge. Here, we experimentally demonstrate efficiently verifiable quantum random sampling in the measurement-based model of quantum computation on a trapped-ion quantum processor. We create random cluster states, which are at the heart of measurement-based computing, up to a size of 4 x 4 qubits. Moreover, by exploiting the structure of these states, we are able to recycle qubits during the computation to sample from entangled cluster states that are larger than the qubit register. We then efficiently estimate the fidelity to verify the prepared states--in single instances and on average--and compare our results to cross-entropy benchmarking. Finally, we study the effect of experimental noise on the certificates. Our results and techniques provide a feasible path toward a verified demonstration of a quantum advantage.

1 aRingbauer, Martin1 aHinsche, Marcel1 aFeldker, Thomas1 aFaehrmann, Paul, K.1 aBermejo-Vega, Juani1 aEdmunds, Claire1 aPostler, Lukas1 aStricker, Roman1 aMarciniak, Christian, D.1 aMeth, Michael1 aPogorelov, Ivan1 aBlatt, Rainer1 aSchindler, Philipp1 aEisert, Jens1 aMonz, Thomas1 aHangleiter, Dominik uhttps://arxiv.org/abs/2307.1442401439nas a2200169 4500008004100000245004200041210004000083260001300123520098600136100002301122700001901145700001501164700001901179700001501198700001901213856003701232 2023 eng d00aA Watermark for Large Language Models0 aWatermark for Large Language Models c6/6/20233 a

Potential harms of large language models can be mitigated by watermarking model output, i.e., embedding signals into generated text that are invisible to humans but algorithmically detectable from a short span of tokens. We propose a watermarking framework for proprietary language models. The watermark can be embedded with negligible impact on text quality, and can be detected using an efficient open-source algorithm without access to the language model API or parameters. The watermark works by selecting a randomized set of "green" tokens before a word is generated, and then softly promoting use of green tokens during sampling. We propose a statistical test for detecting the watermark with interpretable p-values, and derive an information-theoretic framework for analyzing the sensitivity of the watermark. We test the watermark using a multi-billion parameter model from the Open Pretrained Transformer (OPT) family, and discuss robustness and security.

1 aKirchenbauer, John1 aGeiping, Jonas1 aWen, Yuxin1 aKatz, Jonathan1 aMiers, Ian1 aGoldstein, Tom uhttps://arxiv.org/abs/2301.1022602524nas a2200193 4500008004100000245007700041210006900118260001400187520188800201653004302089653002702132653003102159653003302190100001602223700001602239700001902255700001902274856003702293 2022 eng d00aArline Benchmarks: Automated Benchmarking Platform for Quantum Compilers0 aArline Benchmarks Automated Benchmarking Platform for Quantum Co c3/28/20223 a

Efficient compilation of quantum algorithms is vital in the era of Noisy Intermediate-Scale Quantum (NISQ) devices. While multiple open-source quantum compilation and circuit optimization frameworks are available, e.g. IBM Qiskit, CQC Tket, Google Cirq, Rigetti Quilc, PyZX, their relative performance is not always clear to a quantum programmer. The growth of complexity and diversity of quantum circuit compilation algorithms creates a demand for a dedicated tool for cross-benchmarking and profiling of inner workflow of the quantum compilation stack. We present an open-source software package, Arline Benchmarks, that is designed to perform automated benchmarking of quantum compilers with the focus on NISQ applications. The name "Arline" was given in honour of Arline Greenbaum Feynman, the first wife of Richard Feynman, the pioneer of quantum computing. We compared several quantum compilation frameworks based on a set of important metrics such as post-optimization gate counts, circuit depth, hardware-dependent circuit cost function, compiler run time etc. with a detailed analysis of metrics for each compilation stage. We performed a variety of compiler tests for random circuits and structured quantum algorithms (VQE, Trotter decomposition, Grover search, Option Pricing via Amplitude Estimation) for several popular quantum hardware architectures. Leveraging cross-platform functionality of Arline, we propose a concept of composite compilation pipeline that combines compiler-specific circuit optimization subroutines in a single compilation stack and finds an optimized sequence of compilation passes. By providing detailed insights into the compilation flow of quantum compilers, Arline Benchmarks offers a valuable toolkit for quantum computing researchers and software developers to gain additional insights into compilers' characteristics.

10aFOS: Computer and information sciences10aFOS: Physical sciences10aQuantum Physics (quant-ph)10aSoftware Engineering (cs.SE)1 aKharkov, Y.1 aIvanova, A.1 aMikhantiev, E.1 aKotelnikov, A. uhttps://arxiv.org/abs/2202.1402502117nas a2200157 4500008004100000245008300041210006900124260001400193490000800207520162900215100002301844700001601867700001801883700002101901856003701922 2022 eng d00aClassification of (2+1)D invertible fermionic topological phases with symmetry0 aClassification of 21D invertible fermionic topological phases wi c5/30/20220 v1053 a

We provide a classification of invertible topological phases of interacting fermions with symmetry in two spatial dimensions for general fermionic symmetry groups Gf and general values of the chiral central charge c−. Here Gf is a central extension of a bosonic symmetry group Gb by fermion parity, (−1)F, specified by a second cohomology class [ω2]∈H2(Gb,Z2). Our approach proceeds by gauging fermion parity and classifying the resulting Gb symmetry-enriched topological orders while keeping track of certain additional data and constraints. We perform this analysis through two perspectives, using G-crossed braided tensor categories and Spin(2c−)1 Chern-Simons theory coupled to a background G gauge field. These results give a way to characterize and classify invertible fermionic topological phases in terms of a concrete set of data and consistency equations, which is more physically transparent and computationally simpler than the more abstract methods using cobordism theory and spectral sequences. Our results also generalize and provide a different approach to the recent classification of fermionic symmetry-protected topological phases by Wang and Gu, which have chiral central charge c−=0. We show how the 10-fold way classification of topological insulators and superconductors fits into our scheme, along with general non-perturbative constraints due to certain choices of c− and Gf. Mathematically, our results also suggest an explicit general parameterization of deformation classes of (2+1)D invertible topological quantum field theories with Gf symmetry. 

1 aBarkeshli, Maissam1 aChen, Yu-An1 aHsin, Po-Shen1 aManjunath, Naren uhttps://arxiv.org/abs/2109.1103902045nas a2200337 4500008004100000245009200041210006900133260001500202300001100217490000800228520091000236100001301146700001301159700001401172700001701186700002001203700001401223700001401237700001601251700001901267700001801286700001701304700002101321700001501342700002001357700001701377700001701394700001801411700001801429856026001447 2022 eng d00aClosing the Locality and Detection Loopholes in Multiparticle Entanglement Self-Testing0 aClosing the Locality and Detection Loopholes in Multiparticle En c06/23/2022 a2504010 v1283 a

First proposed by Mayers and Yao, self-testing provides a certification method to infer the underlying physics of quantum experiments in a black-box scenario. Numerous demonstrations have been reported to self-test various types of entangled states. However, all the multiparticle self-testing experiments reported so far suffer from both detection and locality loopholes. Here, we report the first experimental realization of multiparticle entanglement self-testing closing the locality loophole in a photonic system, and the detection loophole in a superconducting system, respectively. We certify three-party and four-party GHZ states with at least 0.84 (1) and 0.86 (3) fidelities in a device-independent way. These results can be viewed as a meaningful advance in multiparticle loophole-free self-testing, and also significant progress on the foundations of quantum entanglement certification.

1 aWu, Dian1 aZhao, Qi1 aWang, Can1 aHuang, Liang1 aJiang, Yang-Fan1 aBai, Bing1 aZhou, You1 aGu, Xue-Mei1 aLiu, Feng-Ming1 aMao, Ying-Qiu1 aSun, Qi-Chao1 aChen, Ming-Cheng1 aZhang, Jun1 aPeng, Cheng-Zhi1 aZhu, Xiao-Bo1 aZhang, Qiang1 aLu, Chao-Yang1 aPan, Jian-Wei uhttps://www.researchgate.net/profile/Dian-Wu/publication/361497881_Closing_the_Locality_and_Detection_Loopholes_in_Multiparticle_Entanglement_Self-Testing/links/62b55a8c1010dc02cc57530c/Closing-the-Locality-and-Detection-Loopholes-in-Multiparticle-Entangl01840nas a2200253 4500008004100000245006100041210006000102260001400162520102500176653002701201653003901228653003101267653004701298653005201345100001401397700001301411700001701424700002301441700002501464700001801489700001801507700002401525856003701549 2022 eng d00aContinuous Symmetry Breaking in a Trapped-Ion Spin Chain0 aContinuous Symmetry Breaking in a TrappedIon Spin Chain c11/2/20223 a

One-dimensional systems exhibiting a continuous symmetry can host quantum phases of matter with true long-range order only in the presence of sufficiently long-range interactions. In most physical systems, however, the interactions are short-ranged, hindering the emergence of such phases in one dimension. Here we use a one-dimensional trapped-ion quantum simulator to prepare states with long-range spin order that extends over the system size of up to 23 spins and is characteristic of the continuous symmetry-breaking phase of matter. Our preparation relies on simultaneous control over an array of tightly focused individual-addressing laser beams, generating long-range spin-spin interactions. We also observe a disordered phase with frustrated correlations. We further study the phases at different ranges of interaction and the out-of-equilibrium response to symmetry-breaking perturbations. This work opens an avenue to study new quantum phases and out-of-equilibrium dynamics in low-dimensional systems.

10aFOS: Physical sciences10aQuantum Gases (cond-mat.quant-gas)10aQuantum Physics (quant-ph)10aStatistical Mechanics (cond-mat.stat-mech)10aStrongly Correlated Electrons (cond-mat.str-el)1 aFeng, Lei1 aKatz, Or1 aHaack, Casey1 aMaghrebi, Mohammad1 aGorshkov, Alexey, V.1 aGong, Zhexuan1 aCetina, Marko1 aMonroe, Christopher uhttps://arxiv.org/abs/2211.0127501214nas a2200193 4500008004100000245008100041210006900122260001400191520059300205653003700798653002700835653003100862100001300893700001400906700002100920700002400941700001800965856003700983 2022 eng d00aDemonstration of three- and four-body interactions between trapped-ion spins0 aDemonstration of three and fourbody interactions between trapped c9/12/20223 a

Quantum processors use the native interactions between effective spins to simulate Hamiltonians or execute quantum gates. In most processors, the native interactions are pairwise, limiting the efficiency of controlling entanglement between many qubits. Here we experimentally demonstrate a new class of native interactions between trapped-ion qubits, extending conventional pairwise interactions to higher order. We realize three- and four-body spin interactions as examples, showing that high-order spin polynomials may serve as a new toolbox for quantum information applications.

10aAtomic Physics (physics.atom-ph)10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aKatz, Or1 aFeng, Lei1 aRisinger, Andrew1 aMonroe, Christopher1 aCetina, Marko uhttps://arxiv.org/abs/2209.0569101498nas a2200301 4500008004100000245006800041210006800109260001400177520060600191653002700797653004400824653003100868100001700899700001600916700002500932700001800957700001300975700001800988700001901006700002101025700001401046700002201060700001601082700001901098700001801117700002401135856003701159 2022 eng d00aExperimental Implementation of an Efficient Test of Quantumness0 aExperimental Implementation of an Efficient Test of Quantumness c9/28/20223 a

A test of quantumness is a protocol where a classical user issues challenges to a quantum device to determine if it exhibits non-classical behavior, under certain cryptographic assumptions. Recent attempts to implement such tests on current quantum computers rely on either interactive challenges with efficient verification, or non-interactive challenges with inefficient (exponential time) verification. In this paper, we execute an efficient non-interactive test of quantumness on an ion-trap quantum computer. Our results significantly exceed the bound for a classical device's success.

10aFOS: Physical sciences10aOther Condensed Matter (cond-mat.other)10aQuantum Physics (quant-ph)1 aLewis, Laura1 aZhu, Daiwei1 aGheorghiu, Alexandru1 aNoel, Crystal1 aKatz, Or1 aHarraz, Bahaa1 aWang, Qingfeng1 aRisinger, Andrew1 aFeng, Lei1 aBiswas, Debopriyo1 aEgan, Laird1 aVidick, Thomas1 aCetina, Marko1 aMonroe, Christopher uhttps://arxiv.org/abs/2209.1431601616nas a2200133 4500008004100000245009200041210006900133260001500202490000600217520117300223100002801396700001901424856003901443 2022 eng d00aHow to build Hamiltonians that transport noncommuting charges in quantum thermodynamics0 aHow to build Hamiltonians that transport noncommuting charges in c01/27/20220 v83 a

Noncommuting conserved quantities have recently launched a subfield of quantum thermodynamics. In conventional thermodynamics, a system of interest and a bath exchange quantities -- energy, particles, electric charge, etc. -- that are globally conserved and are represented by Hermitian operators. These operators were implicitly assumed to commute with each other, until a few years ago. Freeing the operators to fail to commute has enabled many theoretical discoveries -- about reference frames, entropy production, resource-theory models, etc. Little work has bridged these results from abstract theory to experimental reality. This paper provides a methodology for building this bridge systematically: We present an algorithm for constructing Hamiltonians that conserve noncommuting quantities globally while transporting the quantities locally. The Hamiltonians can couple arbitrarily many subsystems together and can be integrable or nonintegrable. Special cases of our construction have appeared in quantum chromodynamics (QCD). Our Hamiltonians may be realized physically with superconducting qudits, with ultracold atoms, with trapped ions, and in QCD.

1 aHalpern, Nicole, Yunger1 aMajidy, Shayan uhttps://arxiv.org/abs/2103.14041v100508nas a2200169 4500008004100000245006400041210006300105260001400168300001200182490000800194100001600202700001800218700001800236700002200254700002500276856003700301 2022 eng d00aKramers' degeneracy for open systems in thermal equilibrium0 aKramers degeneracy for open systems in thermal equilibrium c3/10/2022 aL1211040 v1051 aLieu, Simon1 aMcGinley, Max1 aShtanko, Oles1 aCooper, Nigel, R.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2105.0288801505nas a2200205 4500008004100000245006200041210006100103260001500164520083500179653003801014653003401052653004301086653002701129653003101156100002301187700001701210700001701227700001801244856003701262 2022 eng d00aLattice-Based Quantum Advantage from Rotated Measurements0 aLatticeBased Quantum Advantage from Rotated Measurements c10/18/20223 a

Trapdoor claw-free functions (TCFs) are immensely valuable in cryptographic interactions between a classical client and a quantum server. Typically, a protocol has the quantum server prepare a superposition of two-bit strings of a claw and then measure it using Pauli-X or Z measurements. In this paper, we demonstrate a new technique that uses the entire range of qubit measurements from the XY-plane. We show the advantage of this approach in two applications. First, building on (Brakerski et al. 2018, Kalai et al. 2022), we show an optimized two-round proof of quantumness whose security can be expressed directly in terms of the hardness of the LWE (learning with errors) problem. Second, we construct a one-round protocol for blind remote preparation of an arbitrary state on the XY-plane up to a Pauli-Z correction.

10aCryptography and Security (cs.CR)10aEmerging Technologies (cs.ET)10aFOS: Computer and information sciences10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aAlnawakhtha, Yusuf1 aMantri, Atul1 aMiller, Carl1 aWang, Daochen uhttps://arxiv.org/abs/2210.1014302540nas a2200229 4500008004100000245009600041210006900137260001300206490000700219520184300226100002102069700001802090700001402108700001502122700002802137700002302165700002302188700002402211700001802235700002002253856003702273 2022 eng d00aMany-Body Quantum Teleportation via Operator Spreading in the Traversable Wormhole Protocol0 aManyBody Quantum Teleportation via Operator Spreading in the Tra c8/5/20220 v123 a

By leveraging shared entanglement between a pair of qubits, one can teleport a quantum state from one particle to another. Recent advances have uncovered an intrinsically many-body generalization of quantum teleportation, with an elegant and surprising connection to gravity. In particular, the teleportation of quantum information relies on many-body dynamics, which originate from strongly-interacting systems that are holographically dual to gravity; from the gravitational perspective, such quantum teleportation can be understood as the transmission of information through a traversable wormhole. Here, we propose and analyze a new mechanism for many-body quantum teleportation -- dubbed peaked-size teleportation. Intriguingly, peaked-size teleportation utilizes precisely the same type of quantum circuit as traversable wormhole teleportation, yet has a completely distinct microscopic origin: it relies upon the spreading of local operators under generic thermalizing dynamics and not gravitational physics. We demonstrate the ubiquity of peaked-size teleportation, both analytically and numerically, across a diverse landscape of physical systems, including random unitary circuits, the Sachdev-Ye-Kitaev model (at high temperatures), one-dimensional spin chains and a bulk theory of gravity with stringy corrections. Our results pave the way towards using many-body quantum teleportation as a powerful experimental tool for: (i) characterizing the size distributions of operators in strongly-correlated systems and (ii) distinguishing between generic and intrinsically gravitational scrambling dynamics. To this end, we provide a detailed experimental blueprint for realizing many-body quantum teleportation in both trapped ions and Rydberg atom arrays; effects of decoherence and experimental imperfections are analyzed.

1 aSchuster, Thomas1 aKobrin, Bryce1 aGao, Ping1 aCong, Iris1 aKhabiboulline, Emil, T.1 aLinke, Norbert, M.1 aLukin, Mikhail, D.1 aMonroe, Christopher1 aYoshida, Beni1 aYao, Norman, Y. uhttps://arxiv.org/abs/2102.0001000379nas a2200133 4500008004100000022001400041245004500055210004000100260001200140300001400152490000700166100001700173856005500190 2022 eng d a0002-992000aThe Mathematics of Quantum Coin-Flipping0 aMathematics of Quantum CoinFlipping c12/2022 a1908-19170 v691 aMiller, Carl uhttps://www.ams.org/notices/202211/rnoti-p1908.pdf01181nas a2200145 4500008004100000245008000041210006900121260001300190490000800203520073200211100001300943700001800956700002400974856003700998 2022 eng d00aN-body interactions between trapped ion qubits via spin-dependent squeezing0 aNbody interactions between trapped ion qubits via spindependent  c8/5/20220 v1293 a

We describe a simple protocol for the single-step generation of N-body entangling interactions between trapped atomic ion qubits. We show that qubit state-dependent squeezing operations and displacement forces on the collective atomic motion can generate full N-body interactions. Similar to the Mølmer-Sørensen two-body Ising interaction at the core of most trapped ion quantum computers and simulators, the proposed operation is relatively insensitive to the state of motion. We show how this N-body gate operation allows the single-step implementation of a family of N-bit gate operations such as the powerful N-Toffoli gate, which flips a single qubit if and only if all other N-1 qubits are in a particular state.

1 aKatz, Or1 aCetina, Marko1 aMonroe, Christopher uhttps://arxiv.org/abs/2202.0423001696nas a2200145 4500008004100000245005300041210005100094260001500145520127900160100001901439700001401458700001901472700002201491856003701513 2022 eng d00aPost-Quantum Security of the Even-Mansour Cipher0 aPostQuantum Security of the EvenMansour Cipher c12/14/20213 a

The Even-Mansour cipher is a simple method for constructing a (keyed) pseudorandom permutation E from a public random permutation~P:{0,1}n→{0,1}n. It is secure against classical attacks, with optimal attacks requiring qE queries to E and qP queries to P such that qE⋅qP≈2n. If the attacker is given \emph{quantum} access to both E and P, however, the cipher is completely insecure, with attacks using qE,qP=O(n) queries known. In any plausible real-world setting, however, a quantum attacker would have only \emph{classical} access to the keyed permutation~E implemented by honest parties, even while retaining quantum access to~P. Attacks in this setting with qE⋅q2P≈2n are known, showing that security degrades as compared to the purely classical case, but leaving open the question as to whether the Even-Mansour cipher can still be proven secure in this natural, "post-quantum" setting. We resolve this question, showing that any attack in that setting requires qE⋅q2P+qP⋅q2E≈2n. Our results apply to both the two-key and single-key variants of Even-Mansour. Along the way, we establish several generalizations of results from prior work on quantum-query lower bounds that may be of independent interest. 

1 aAlagic, Gorjan1 aBai, Chen1 aKatz, Jonathan1 aMajenz, Christian uhttps://arxiv.org/abs/2112.0753001152nas a2200157 4500008004100000245007900041210006900120260001400189520065900203100001900862700001400881700001900895700002200914700002000936856003800956 2022 eng d00aPost-Quantum Security of the (Tweakable) FX Construction, and Applications0 aPostQuantum Security of the Tweakable FX Construction and Applic c8/29/20223 a

The FX construction provides a way to increase the effective key length of a block cipher E. We prove security of a tweakable version of the FX construction in the post-quantum setting, i.e., against a quantum attacker given only classical access to the secretly keyed construction while retaining quantum access to E, a setting that seems to be the most relevant one for real-world applications. We then use our results to prove post-quantum security—in the same model—of the (plain) FX construction, Elephant (a finalist of NIST's lightweight cryptography standardization effort), and Chaskey (an ISO-standardized lightweight MAC

1 aAlagic, Gorjan1 aBai, Chen1 aKatz, Jonathan1 aMajenz, Christian1 aStruck, Patrick uhttps://eprint.iacr.org/2022/109702380nas a2200181 4500008004100000245007100041210006900112260001400181300000800195490000600203520186000209100001302069700002302082700002402105700001902129700001302148856003702161 2022 eng d00aProvably accurate simulation of gauge theories and bosonic systems0 aProvably accurate simulation of gauge theories and bosonic syste c9/20/2022 a8160 v63 a

Quantum many-body systems involving bosonic modes or gauge fields have infinite-dimensional local Hilbert spaces which must be truncated to perform simulations of real-time dynamics on classical or quantum computers. To analyze the truncation error, we develop methods for bounding the rate of growth of local quantum numbers such as the occupation number of a mode at a lattice site, or the electric field at a lattice link. Our approach applies to various models of bosons interacting with spins or fermions, and also to both abelian and non-abelian gauge theories. We show that if states in these models are truncated by imposing an upper limit Λ on each local quantum number, and if the initial state has low local quantum numbers, then an error at most ϵ can be achieved by choosing Λ to scale polylogarithmically with ϵ−1, an exponential improvement over previous bounds based on energy conservation. For the Hubbard-Holstein model, we numerically compute a bound on Λ that achieves accuracy ϵ, obtaining significantly improved estimates in various parameter regimes. We also establish a criterion for truncating the Hamiltonian with a provable guarantee on the accuracy of time evolution. Building on that result, we formulate quantum algorithms for dynamical simulation of lattice gauge theories and of models with bosonic modes; the gate complexity depends almost linearly on spacetime volume in the former case, and almost quadratically on time in the latter case. We establish a lower bound showing that there are systems involving bosons for which this quadratic scaling with time cannot be improved. By applying our result on the truncation error in time evolution, we also prove that spectrally isolated energy eigenstates can be approximated with accuracy ϵ by truncating local quantum numbers at Λ=polylog(ϵ−1).

1 aTong, Yu1 aAlbert, Victor, V.1 aMcClean, Jarrod, R.1 aPreskill, John1 aSu, Yuan uhttps://arxiv.org/abs/2110.0694202013nas a2200277 4500008004100000245008100041210006900122260001300191300001300204490000600217520120300223100002301426700001801449700002001467700002101487700002001508700002001528700001701548700002101565700001401586700001701600700002401617700002001641700001501661856005901676 2022 eng d00aQuantum computational advantage via high-dimensional Gaussian boson sampling0 aQuantum computational advantage via highdimensional Gaussian bos c1/5/2022 aeabi78940 v83 a

A programmable quantum computer based on fiber optics outperforms classical computers with a high level of confidence. Photonics is a promising platform for demonstrating a quantum computational advantage (QCA) by outperforming the most powerful classical supercomputers on a well-defined computational task. Despite this promise, existing proposals and demonstrations face challenges. Experimentally, current implementations of Gaussian boson sampling (GBS) lack programmability or have prohibitive loss rates. Theoretically, there is a comparative lack of rigorous evidence for the classical hardness of GBS. In this work, we make progress in improving both the theoretical evidence and experimental prospects. We provide evidence for the hardness of GBS, comparable to the strongest theoretical proposals for QCA. We also propose a QCA architecture we call high-dimensional GBS, which is programmable and can be implemented with low loss using few optical components. We show that particular algorithms for simulating GBS are outperformed by high-dimensional GBS experiments at modest system sizes. This work thus opens the path to demonstrating QCA with programmable photonic processors.

1 aDeshpande, Abhinav1 aMehta, Arthur1 aVincent, Trevor1 aQuesada, Nicolas1 aHinsche, Marcel1 aIoannou, Marios1 aMadsen, Lars1 aLavoie, Jonathan1 aQi, Haoyu1 aEisert, Jens1 aHangleiter, Dominik1 aFefferman, Bill1 aDhand, Ish uhttps://www.science.org/doi/abs/10.1126/sciadv.abi789402845nas a2200541 4500008004100000245004700041210004700088260001300135520125300148653002701401653004401428653004901472653004201521653002901563653003101592100002501623700002001648700002101668700002501689700002001714700002201734700002001756700002001776700001801796700002101814700002101835700001601856700001801872700001501890700001901905700002101924700002401945700002201969700001801991700001902009700002002028700002402048700002402072700002302096700001902119700002002138700002202158700001802180700002102198700002602219700002102245856003702266 2022 eng d00aQuantum Simulation for High Energy Physics0 aQuantum Simulation for High Energy Physics c4/7/20223 a

It is for the first time that Quantum Simulation for High Energy Physics (HEP) is studied in the U.S. decadal particle-physics community planning, and in fact until recently, this was not considered a mainstream topic in the community. This fact speaks of a remarkable rate of growth of this subfield over the past few years, stimulated by the impressive advancements in Quantum Information Sciences (QIS) and associated technologies over the past decade, and the significant investment in this area by the government and private sectors in the U.S. and other countries. High-energy physicists have quickly identified problems of importance to our understanding of nature at the most fundamental level, from tiniest distances to cosmological extents, that are intractable with classical computers but may benefit from quantum advantage. They have initiated, and continue to carry out, a vigorous program in theory, algorithm, and hardware co-design for simulations of relevance to the HEP mission. This community whitepaper is an attempt to bring this exciting and yet challenging area of research to the spotlight, and to elaborate on what the promises, requirements, challenges, and potential solutions are over the next decade and beyond.

10aFOS: Physical sciences10aHigh Energy Physics - Lattice (hep-lat)10aHigh Energy Physics - Phenomenology (hep-ph)10aHigh Energy Physics - Theory (hep-th)10aNuclear Theory (nucl-th)10aQuantum Physics (quant-ph)1 aBauer, Christian, W.1 aDavoudi, Zohreh1 aBalantekin, Baha1 aBhattacharya, Tanmoy1 aCarena, Marcela1 ade Jong, Wibe, A.1 aDraper, Patrick1 aEl-Khadra, Aida1 aGemelke, Nate1 aHanada, Masanori1 aKharzeev, Dmitri1 aLamm, Henry1 aLi, Ying-Ying1 aLiu, Junyu1 aLukin, Mikhail1 aMeurice, Yannick1 aMonroe, Christopher1 aNachman, Benjamin1 aPagano, Guido1 aPreskill, John1 aRinaldi, Enrico1 aRoggero, Alessandro1 aSantiago, David, I.1 aSavage, Martin, J.1 aSiddiqi, Irfan1 aSiopsis, George1 aVan Zanten, David1 aWiebe, Nathan1 aYamauchi, Yukari1 aYeter-Aydeniz, Kübra1 aZorzetti, Silvia uhttps://arxiv.org/abs/2204.0338101714nas a2200181 4500008004100000245004400041210004400085260001500129490000800144520120900152100002801361700002801389700002101417700002001438700001701458700002001475856003701495 2022 eng d00aResource theory of quantum uncomplexity0 aResource theory of quantum uncomplexity c12/19/20220 v1063 a

Quantum complexity is emerging as a key property of many-body systems, including black holes, topological materials, and early quantum computers. A state's complexity quantifies the number of computational gates required to prepare the state from a simple tensor product. The greater a state's distance from maximal complexity, or "uncomplexity," the more useful the state is as input to a quantum computation. Separately, resource theories -- simple models for agents subject to constraints -- are burgeoning in quantum information theory. We unite the two domains, confirming Brown and Susskind's conjecture that a resource theory of uncomplexity can be defined. The allowed operations, fuzzy operations, are slightly random implementations of two-qubit gates chosen by an agent. We formalize two operational tasks, uncomplexity extraction and expenditure. Their optimal efficiencies depend on an entropy that we engineer to reflect complexity. We also present two monotones, uncomplexity measures that decline monotonically under fuzzy operations, in certain regimes. This work unleashes on many-body complexity the resource-theory toolkit from quantum information theory.

1 aHalpern, Nicole, Yunger1 aKothakonda, Naga, B. T.1 aHaferkamp, Jonas1 aMunson, Anthony1 aEisert, Jens1 aFaist, Philippe uhttps://arxiv.org/abs/2110.1137101649nas a2200193 4500008004100000245007500041210006900116260001300185490000600198520110000204100001401304700001301318700001701331700001301348700002101361700001801382700001801400856003701418 2022 eng d00aA scheme to create and verify scalable entanglement in optical lattice0 ascheme to create and verify scalable entanglement in optical lat c9/4/20220 v83 a

To achieve scalable quantum information processing, great efforts have been devoted to the creation of large-scale entangled states in various physical systems. Ultracold atom in optical lattice is considered as one of the promising platforms due to its feasible initialization and parallel manipulation. In this work, we propose an efficient scheme to generate and characterize global entanglement in the optical lattice. With only two-layer quantum circuits, the generation utilizes two-qubit entangling gates based on the superexchange interaction in double wells. The parallelism of these operations enables the generation to be fast and scalable. To verify the entanglement of this non-stabilizer state, we mainly design three complementary detection protocols which are less resource-consuming compared to the full tomography. In particular, one just needs two homogenous local measurement settings to identify the entanglement property. Our entanglement generation and verification protocols provide the foundation for the further quantum information processing in optical lattice.

1 aZhou, You1 aXiao, Bo1 aDa Li, Meng-1 aZhao, Qi1 aYuan, Zhen-Sheng1 aMa, Xiongfeng1 aPan, Jian-Wei uhttps://arxiv.org/abs/2209.0153101392nas a2200229 4500008004100000245008100041210006900122260001400191520061400205653002700819653005300846653004900899653003100948100001900979700001700998700001901015700002001034700002401054700002501078700002201103856003701125 2022 eng d00aSnowmass 2021 White Paper: Tabletop experiments for infrared quantum gravity0 aSnowmass 2021 White Paper Tabletop experiments for infrared quan c3/22/20223 a

Progress in the quantum readout and control of mechanical devices from single atoms to large masses may enable a first generation of experiments probing the gravitational interaction in the quantum regime, conceivably within the next decade. In this Snowmass whitepaper, we briefly outline the possibilities and challenges facing the realization of these experiments. In particular, we emphasize the need for detailed theories of modifications to the usual effective QFT of gravitons in the infrared regime E/L3≪mPl/ℓ3Pl in which these experiments operate, and relations to possible UV completions.

10aFOS: Physical sciences10aGeneral Relativity and Quantum Cosmology (gr-qc)10aHigh Energy Physics - Phenomenology (hep-ph)10aQuantum Physics (quant-ph)1 aCarney, Daniel1 aChen, Yanbei1 aGeraci, Andrew1 aMüller, Holger1 aPanda, Cristian, D.1 aStamp, Philip, C. E.1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2203.1184602149nas a2200457 4500008004100000245005300041210005200094260001400146520077300160653005700933653002700990653004601017653004901063100003401112700002201146700002101168700001901189700001901208700002201227700001901249700002201268700002501290700001901315700001701334700001901351700002101370700002101391700001801412700001401430700002701444700002201471700002201493700001601515700002001531700001701551700002501568700002201593700001401615700002501629856003701654 2022 eng d00aSnowmass 2021 White Paper: The Windchime Project0 aSnowmass 2021 White Paper The Windchime Project c3/14/20223 a

The absence of clear signals from particle dark matter in direct detection experiments motivates new approaches in disparate regions of viable parameter space. In this Snowmass white paper, we outline the Windchime project, a program to build a large array of quantum-enhanced mechanical sensors. The ultimate aim is to build a detector capable of searching for Planck mass-scale dark matter purely through its gravitational coupling to ordinary matter. In the shorter term, we aim to search for a number of other physics targets, especially some ultralight dark matter candidates. Here, we discuss the basic design, open R&D challenges and opportunities, current experimental efforts, and both short- and long-term physics targets of the Windchime project.

10aCosmology and Nongalactic Astrophysics (astro-ph.CO)10aFOS: Physical sciences10aHigh Energy Physics - Experiment (hep-ex)10aHigh Energy Physics - Phenomenology (hep-ph)1 aCollaboration, The, Windchime1 aAttanasio, Alaina1 aBhave, Sunil, A.1 aBlanco, Carlos1 aCarney, Daniel1 aDemarteau, Marcel1 aElshimy, Bahaa1 aFebbraro, Michael1 aFeldman, Matthew, A.1 aGhosh, Sohitri1 aHickin, Abby1 aHong, Seongjin1 aLang, Rafael, F.1 aLawrie, Benjamin1 aLi, Shengchao1 aLiu, Zhen1 aMaldonado, Juan, P. A.1 aMarvinney, Claire1 aOo, Hein, Zay Yar1 aPai, Yun-Yi1 aPooser, Raphael1 aQin, Juehang1 aSparmann, Tobias, J.1 aTaylor, Jacob, M.1 aTian, Hao1 aTunnell, Christopher uhttps://arxiv.org/abs/2203.0724202778nas a2200241 4500008004100000245009900041210006900140260001100209520197600220100001902196700001702215700001802232700001602250700001602266700001702282700002202299700001702321700001802338700001802356700001702374700002102391856012402412 2022 eng d00aStatus Report on the Third Round of the NIST Post-Quantum Cryptography Standardization Process0 aStatus Report on the Third Round of the NIST PostQuantum Cryptog c7/20223 a

The National Institute of Standards and Technology is in the process of selecting publickey cryptographic algorithms through a public, competition-like process. The new publickey cryptography standards will specify additional digital signature, public-key encryption, and key-establishment algorithms to augment Federal Information Processing Standard (FIPS) 186-4, Digital Signature Standard (DSS), as well as NIST Special Publication (SP) 800-56A Revision 3, Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography, and SP 800-56B Revision 2, Recommendation for Pair-Wise Key Establishment Using Integer Factorization Cryptography. It is intended that these algorithms will be capable of protecting sensitive information well into the foreseeable future, including after the advent of quantum computers.

This report describes the evaluation and selection process of the NIST Post-Quantum Cryptography Standardization process third-round candidates based on public feedback and internal review. The report summarizes each of the 15 third-round candidate algorithms and identifies those selected for standardization, as well as those that will continue to be evaluated in a fourth round of analysis. The public-key encryption and key-establishment algorithm that will be standardized is CRYSTALS–KYBER. The digital signatures that will be standardized are CRYSTALS–Dilithium, FALCON, and SPHINCS+. While there are multiple signature algorithms selected, NIST recommends CRYSTALS–Dilithium as the primary algorithm to be implemented. In addition, four of the alternate key-establishment candidate algorithms will advance to a fourth round of evaluation: BIKE, Classic McEliece, HQC, and SIKE. These candidates are still being considered for future standardization. NIST will also issue a new Call for Proposals for public-key digital signature algorithms to augment and diversify its signature portfolio.

1 aAlagic, Gorjan1 aApon, Daniel1 aCooper, David1 aDang, Quynh1 aDang, Thinh1 aKelsey, John1 aLichtinger, Jacob1 aMiller, Carl1 aMoody, Dustin1 aPeralta, Rene1 aPerlner, Ray1 aRobinson, Angela uhttps://www.quics.umd.edu/publications/status-report-third-round-nist-post-quantum-cryptography-standardization-process01763nas a2200169 4500008004100000245007700041210006900118260001500187490000600202520123700208100002101445700002601466700002101492700001901513700002401532856003701556 2022 eng d00aTheoretical bounds on data requirements for the ray-based classification0 aTheoretical bounds on data requirements for the raybased classif c02/26/20220 v33 a

The problem of classifying high-dimensional shapes in real-world data grows in complexity as the dimension of the space increases. For the case of identifying convex shapes of different geometries, a new classification framework has recently been proposed in which the intersections of a set of one-dimensional representations, called rays, with the boundaries of the shape are used to identify the specific geometry. This ray-based classification (RBC) has been empirically verified using a synthetic dataset of two- and three-dimensional shapes [1] and, more recently, has also been validated experimentally [2]. Here, we establish a bound on the number of rays necessary for shape classification, defined by key angular metrics, for arbitrary convex shapes. For two dimensions, we derive a lower bound on the number of rays in terms of the shape's length, diameter, and exterior angles. For convex polytopes in R^N, we generalize this result to a similar bound given as a function of the dihedral angle and the geometrical parameters of polygonal faces. This result enables a different approach for estimating high-dimensional shapes using substantially fewer data elements than volumetric or surface-based approaches.

1 aWeber, Brian, J.1 aKalantre, Sandesh, S.1 aMcJunkin, Thomas1 aTaylor, J., M.1 aZwolak, Justyna, P. uhttps://arxiv.org/abs/2103.0957701353nas a2200145 4500008004100000245003500041210003500076260001400111520095600125100002801081700002201109700001801131700002101149856003701170 2022 eng d00aTopological Edge Mode Tapering0 aTopological Edge Mode Tapering c6/14/20223 a

Mode tapering, or the gradual manipulation of the size of some mode, is a requirement for any system that aims to efficiently interface two or more subsystems of different mode sizes. While high efficiency tapers have been demonstrated, they often come at the cost of a large device footprint or challenging fabrication. Topological photonics, offering robustness to certain types of disorder as well as chirality, has proved to be a well-suited design principle for numerous applications in recent years. Here we present a new kind of mode taper realized through topological bandgap engineering. We numerically demonstrate a sixfold change in mode width over an extremely compact 8μm distance with near unity efficiency in the optical domain. With suppressed backscattering and no excitation of higher-order modes, such a taper could enable new progress in the development of scalable, multi-component systems in classical and quantum optics.

1 aFlower, Christopher, J.1 aBarik, Sabyasachi1 aMittal, Sunil1 aHafezi, Mohammad uhttps://arxiv.org/abs/2206.0705601880nas a2200229 4500008004100000245005800041210005800099260001500157490000700172520123000179100002001409700002101429700001701450700002601467700002001493700001701513700001801530700001901548700002201567700002401589856003701613 2022 eng d00aToward Robust Autotuning of Noisy Quantum dot Devices0 aToward Robust Autotuning of Noisy Quantum dot Devices c02/26/20220 v173 a

The current autotuning approaches for quantum dot (QD) devices, while showing some success, lack an assessment of data reliability. This leads to unexpected failures when noisy or otherwise low-quality data is processed by an autonomous system. In this work, we propose a framework for robust autotuning of QD devices that combines a machine learning (ML) state classifier with a data quality control module. The data quality control module acts as a "gatekeeper" system, ensuring that only reliable data are processed by the state classifier. Lower data quality results in either device recalibration or termination. To train both ML systems, we enhance the QD simulation by incorporating synthetic noise typical of QD experiments. We confirm that the inclusion of synthetic noise in the training of the state classifier significantly improves the performance, resulting in an accuracy of 95.0(9) % when tested on experimental data. We then validate the functionality of the data quality control module by showing that the state classifier performance deteriorates with decreasing data quality, as expected. Our results establish a robust and flexible ML framework for autonomous tuning of noisy QD devices.

1 aZiegler, Joshua1 aMcJunkin, Thomas1 aJoseph, E.S.1 aKalantre, Sandesh, S.1 aHarpt, Benjamin1 aSavage, D.E.1 aLagally, M.G.1 aEriksson, M.A.1 aTaylor, Jacob, M.1 aZwolak, Justyna, P. uhttps://arxiv.org/abs/2108.0004300564nas a2200133 4500008004100000022001400041245003000055210003000085260001400115520019700129100002300326700001700349856006400366 2022 eng d a1745-247300aWhere we are with quantum0 aWhere we are with quantum c4/28/20223 a

A theoretical analysis shows how a person’s location in space could be verified by the transmission of single photons. A vital application of quantum networks may be within reach.

1 aAlnawakhtha, Yusuf1 aMiller, Carl uhttps://www.quics.umd.edu/publications/where-we-are-quantum02266nas a2200133 4500008004100000245003400041210003300075260001400108520190700122100001902029700002502048700002202073856003702095 2021 eng d00aCan you sign a quantum state?0 aCan you sign a quantum state c12/6/20213 a

Cryptography with quantum states exhibits a number of surprising and counterintuitive features. In a 2002 work, Barnum et al. argued informally that these strange features should imply that digital signatures for quantum states are impossible (Barnum et al., FOCS 2002). In this work, we perform the first rigorous study of the problem of signing quantum states. We first show that the intuition of Barnum et al. was correct, by proving an impossibility result which rules out even very weak forms of signing quantum states. Essentially, we show that any non-trivial combination of correctness and security requirements results in negligible security. This rules out all quantum signature schemes except those which simply measure the state and then sign the outcome using a classical scheme. In other words, only classical signature schemes exist. We then show a positive result: it is possible to sign quantum states, provided that they are also encrypted with the public key of the intended recipient. Following classical nomenclature, we call this notion quantum signcryption. Classically, signcryption is only interesting if it provides superior efficiency to simultaneous encryption and signing. Our results imply that, quantumly, it is far more interesting: by the laws of quantum mechanics, it is the only signing method available. We develop security definitions for quantum signcryption, ranging from a simple one-time two-user setting, to a chosen-ciphertext-secure many-time multi-user setting. We also give secure constructions based on post-quantum public-key primitives. Along the way, we show that a natural hybrid method of combining classical and quantum schemes can be used to "upgrade" a secure classical scheme to the fully-quantum setting, in a wide range of cryptographic settings including signcryption, authenticated encryption, and chosen-ciphertext security.

1 aAlagic, Gorjan1 aGagliardoni, Tommaso1 aMajenz, Christian uhttps://arxiv.org/abs/1811.1185801979nas a2200277 4500008004100000245007600041210006900117260001400186520117400200100001301374700001801387700002101405700002901426700001601455700002001471700001801491700001501509700002001524700002301544700001801567700002101585700001801606700002101624700001901645856003701664 2021 eng d00aChiral transport of hot carriers in graphene in the quantum Hall regime0 aChiral transport of hot carriers in graphene in the quantum Hall c10/3/20213 a

Photocurrent (PC) measurements can reveal the relaxation dynamics of photo-excited hot carriers beyond the linear response of conventional transport experiments, a regime important for carrier multiplication. In graphene subject to a magnetic field, PC measurements are able to probe the existence of Landau levels with different edge chiralities which is exclusive to relativistic electron systems. Here, we report the accurate measurement of PC in graphene in the quantum Hall regime. Prominent PC oscillations as a function of gate voltage on samples' edges are observed. These oscillation amplitudes form an envelope which depends on the strength of the magnetic field, as does the PCs' power dependence and their saturation behavior. We explain these experimental observations through a model using optical Bloch equations, incorporating relaxations through acoustic-, optical- phonons and Coulomb interactions. The simulated PC agrees with our experimental results, leading to a unified understanding of the chiral PC in graphene at various magnetic field strengths, and providing hints for the occurrence of a sizable carrier multiplication. 

1 aCao, Bin1 aGrass, Tobias1 aGazzano, Olivier1 aPatel, Kishan, Ashokbhai1 aHu, Jiuning1 aMüller, Markus1 aHuber, Tobias1 aAnzi, Luca1 aWatanabe, Kenji1 aTaniguchi, Takashi1 aNewell, David1 aGullans, Michael1 aSordan, Roman1 aHafezi, Mohammad1 aSolomon, Glenn uhttps://arxiv.org/abs/2110.0107900790nas a2200133 4500008004100000245009400041210006900135260001400204520034000218100001900558700002000577700002200597856003700619 2021 eng d00aComment on "Using an atom interferometer to infer gravitational entanglement generation''0 aComment on Using an atom interferometer to infer gravitational e c11/8/20213 a

Our paper arXiv:2101.11629 contains a technical error which changes some of the conclusions. We thank Streltsov, Pedernales, and Plenio for bringing the essence of this error to our attention. Here we explain the error, examine its consequences, and suggest methods to overcome the resulting weakness in the proposed experiment.

1 aCarney, Daniel1 aMüller, Holger1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2111.0466701894nas a2200301 4500008004100000245006400041210006300105260001400168520102800182100001601210700001701226700001801243700002101261700002201282700001601304700001701320700002201337700003001359700002201389700001901411700002101430700001801451700001801469700002301487700002101510700002401531856003701555 2021 eng d00aCross-Platform Comparison of Arbitrary Quantum Computations0 aCrossPlatform Comparison of Arbitrary Quantum Computations c7/27/20213 a

As we approach the era of quantum advantage, when quantum computers (QCs) can outperform any classical computer on particular tasks, there remains the difficult challenge of how to validate their performance. While algorithmic success can be easily verified in some instances such as number factoring or oracular algorithms, these approaches only provide pass/fail information for a single QC. On the other hand, a comparison between different QCs on the same arbitrary circuit provides a lower-bound for generic validation: a quantum computation is only as valid as the agreement between the results produced on different QCs. Such an approach is also at the heart of evaluating metrological standards such as disparate atomic clocks. In this paper, we report a cross-platform QC comparison using randomized and correlated measurements that results in a wealth of information on the QC systems. We execute several quantum circuits on widely different physical QC platforms and analyze the cross-platform fidelities.

1 aZhu, Daiwei1 aCian, Ze-Pei1 aNoel, Crystal1 aRisinger, Andrew1 aBiswas, Debopriyo1 aEgan, Laird1 aZhu, Yingyue1 aGreen, Alaina, M.1 aAlderete, Cinthia, Huerta1 aNguyen, Nhung, H.1 aWang, Qingfeng1 aMaksymov, Andrii1 aNam, Yunseong1 aCetina, Marko1 aLinke, Norbert, M.1 aHafezi, Mohammad1 aMonroe, Christopher uhttps://arxiv.org/abs/2107.1138702085nas a2200169 4500008004100000245004300041210004300084260001300127520161100140100002001751700002501771700002401796700002101820700001801841700001901859856003701878 2021 eng d00aCrystallography of Hyperbolic Lattices0 aCrystallography of Hyperbolic Lattices c5/3/20213 a

Hyperbolic lattices are a revolutionary platform for tabletop simulations of holography and quantum physics in curved space and facilitate efficient quantum error correcting codes. Their underlying geometry is non-Euclidean, and the absence of Bloch's theorem precludes a simple understanding of their band structure. Motivated by recent insights into hyperbolic band theory, we initiate a crystallography of hyperbolic lattices. We show that many hyperbolic lattices feature a hidden crystal structure characterized by unit cells, hyperbolic Bravais lattices, and associated symmetry groups. Using the mathematical framework of higher-genus Riemann surfaces and Fuchsian groups, we derive, for the first time, a list of example hyperbolic {p,q} lattices and their hyperbolic Bravais lattices, including five infinite families and several graphs relevant for experiments in circuit quantum electrodynamics and topolectrical circuits. Our results find application for both finite and infinite hyperbolic lattices. We describe a method to efficiently generate finite hyperbolic lattices of arbitrary size and explain why the present crystallography is the first step towards a complete band theory of hyperbolic lattices and apply it to construct Bloch wave Hamiltonians. This work lays the foundation for generalizing some of the most powerful concepts of solid state physics, such as crystal momentum and Brillouin zone, to the emerging field of hyperbolic lattices and tabletop simulations of gravitational theories, and reveals the connections to concepts from topology and algebraic geometry.

1 aBoettcher, Igor1 aGorshkov, Alexey, V.1 aKollár, Alicia, J.1 aMaciejko, Joseph1 aRayan, Steven1 aThomale, Ronny uhttps://arxiv.org/abs/2105.0108702078nas a2200277 4500008004100000245006700041210006600108260001500174520125200189100002201441700001801463700002501481700002101506700002401527700002501551700002101576700002001597700002501617700002601642700001601668700001901684700002301703700001801726700001901744856003701763 2021 eng d00aDevice-independent Randomness Expansion with Entangled Photons0 aDeviceindependent Randomness Expansion with Entangled Photons c01/28/20213 a

With the growing availability of experimental loophole-free Bell tests, it has become possible to implement a new class of device-independent random number generators whose output can be certified to be uniformly random without requiring a detailed model of the quantum devices used. However, all of these experiments require many input bits in order to certify a small number of output bits, and it is an outstanding challenge to develop a system that generates more randomness than is used. Here, we devise a device-independent spot-checking protocol which uses only uniform bits as input. Implemented with a photonic loophole-free Bell test, we can produce 24% more certified output bits (1,181,264,237) than consumed input bits (953,301,640), which is 5 orders of magnitude more efficient than our previous work [arXiv:1812.07786]. The experiment ran for 91.0 hours, creating randomness at an average rate of 3606 bits/s with a soundness error bounded by 5.7×10−7 in the presence of classical side information. Our system will allow for greater trust in public sources of randomness, such as randomness beacons, and the protocols may one day enable high-quality sources of private randomness as the device footprint shrinks.

1 aShalm, Lynden, K.1 aZhang, Yanbao1 aBienfang, Joshua, C.1 aSchlager, Collin1 aStevens, Martin, J.1 aMazurek, Michael, D.1 aAbellán, Carlos1 aAmaya, Waldimar1 aMitchell, Morgan, W.1 aAlhejji, Mohammad, A.1 aFu, Honghao1 aOrnstein, Joel1 aMirin, Richard, P.1 aNam, Sae, Woo1 aKnill, Emanuel uhttps://arxiv.org/abs/1912.1115801622nas a2200145 4500008004100000245008500041210006900126260001400195520114800209100002201357700002101379700002101400700001801421856003701439 2021 eng d00aEfficient quantum programming using EASE gates on a trapped-ion quantum computer0 aEfficient quantum programming using EASE gates on a trappedion q c7/15/20213 a

Parallel operations in conventional computing have proven to be an essential tool for efficient and practical computation, and the story is not different for quantum computing. Indeed, there exists a large body of works that study advantages of parallel implementations of quantum gates for efficient quantum circuit implementations. Here, we focus on the recently invented efficient, arbitrary, simultaneously entangling (EASE) gates, available on a trapped-ion quantum computer. Leveraging its flexibility in selecting arbitrary pairs of qubits to be coupled with any degrees of entanglement, all in parallel, we show a n-qubit Clifford circuit can be implemented using 6log(n) EASE gates, a n-qubit multiply-controlled NOT gate can be implemented using 3n/2 EASE gates, and a n-qubit permutation can be implemented using six EASE gates. We discuss their implications to near-term quantum chemistry simulations and the state of the art pattern matching algorithm. Given Clifford + multiply-controlled NOT gates form a universal gate set for quantum computing, our results imply efficient quantum computation by EASE gates, in general.

1 aGrzesiak, Nikodem1 aMaksymov, Andrii1 aNiroula, Pradeep1 aNam, Yunseong uhttps://arxiv.org/abs/2107.0759101588nas a2200241 4500008004100000022001400041245008300055210006900138260001400207300001100221490000600232520086600238100002401104700002201128700002101150700001801171700002801189700001401217700002401231700002301255700002101278856004701299 2021 eng d a2058-956500aEntangled quantum cellular automata, physical complexity, and Goldilocks rules0 aEntangled quantum cellular automata physical complexity and Gold c9/29/2021 a0450170 v63 a

Cellular automata are interacting classical bits that display diverse emergent behaviors, from fractals to random-number generators to Turing-complete computation. We discover that quantum cellular automata (QCA) can exhibit complexity in the sense of the complexity science that describes biology, sociology, and economics. QCA exhibit complexity when evolving under "Goldilocks rules" that we define by balancing activity and stasis. Our Goldilocks rules generate robust dynamical features (entangled breathers), network structure and dynamics consistent with complexity, and persistent entropy fluctuations. Present-day experimental platforms -- Rydberg arrays, trapped ions, and superconducting qubits -- can implement our Goldilocks protocols, making testable the link between complexity science and quantum computation exposed by our QCA.

1 aHillberry, Logan, E1 aJones, Matthew, T1 aVargas, David, L1 aRall, Patrick1 aHalpern, Nicole, Yunger1 aBao, Ning1 aNotarnicola, Simone1 aMontangero, Simone1 aCarr, Lincoln, D uhttp://dx.doi.org/10.1088/2058-9565/ac1c4100984nas a2200133 4500008004100000245005500041210005100096260001400147520059000161100002600751700001700777700001900794856003700813 2021 eng d00aAn explicit vector algorithm for high-girth MaxCut0 aexplicit vector algorithm for highgirth MaxCut c8/27/20213 a

We give an approximation algorithm for MaxCut and provide guarantees on the average fraction of edges cut on d-regular graphs of girth ≥2k. For every d≥3 and k≥4, our approximation guarantees are better than those of all other classical and quantum algorithms known to the authors. Our algorithm constructs an explicit vector solution to the standard semidefinite relaxation of MaxCut and applies hyperplane rounding. It may be viewed as a simplification of the previously best known technique, which approximates Gaussian wave processes on the infinite d-regular tree.

1 aThompson, Jessica, K.1 aParekh, Ojas1 aMarwaha, Kunal uhttps://arxiv.org/abs/2108.1247702349nas a2200313 4500008004100000245007100041210006900112260001400181520145100195100001601646700003401662700001701696700001801713700001301731700001801744700001901762700002101781700001401802700002201816700001601838700002501854700001801879700001901897700002001916700002001936700001801956700002401974856003701998 2021 eng d00aInteractive Protocols for Classically-Verifiable Quantum Advantage0 aInteractive Protocols for ClassicallyVerifiable Quantum Advantag c12/9/20213 a

Achieving quantum computational advantage requires solving a classically intractable problem on a quantum device. Natural proposals rely upon the intrinsic hardness of classically simulating quantum mechanics; however, verifying the output is itself classically intractable. On the other hand, certain quantum algorithms (e.g. prime factorization via Shor's algorithm) are efficiently verifiable, but require more resources than what is available on near-term devices. One way to bridge the gap between verifiability and implementation is to use "interactions" between a prover and a verifier. By leveraging cryptographic functions, such protocols enable the classical verifier to enforce consistency in a quantum prover's responses across multiple rounds of interaction. In this work, we demonstrate the first implementation of an interactive quantum advantage protocol, using an ion trap quantum computer. We execute two complementary protocols -- one based upon the learning with errors problem and another where the cryptographic construction implements a computational Bell test. To perform multiple rounds of interaction, we implement mid-circuit measurements on a subset of trapped ion qubits, with subsequent coherent evolution. For both protocols, the performance exceeds the asymptotic bound for classical behavior; maintaining this fidelity at scale would conclusively demonstrate verifiable quantum advantage.

1 aZhu, Daiwei1 aKahanamoku-Meyer, Gregory, D.1 aLewis, Laura1 aNoel, Crystal1 aKatz, Or1 aHarraz, Bahaa1 aWang, Qingfeng1 aRisinger, Andrew1 aFeng, Lei1 aBiswas, Debopriyo1 aEgan, Laird1 aGheorghiu, Alexandru1 aNam, Yunseong1 aVidick, Thomas1 aVazirani, Umesh1 aYao, Norman, Y.1 aCetina, Marko1 aMonroe, Christopher uhttps://arxiv.org/abs/2112.0515601652nas a2200133 4500008004100000245005900041210005900100260001500159520124500174100001901419700002201438700002101460856003701481 2021 eng d00aLefschetz Thimble Quantum Monte Carlo for Spin Systems0 aLefschetz Thimble Quantum Monte Carlo for Spin Systems c10/20/20213 a

Monte Carlo simulations are often useful tools for modeling quantum systems, but in some cases they suffer from a sign problem, which manifests as an oscillating phase attached to the probabilities being sampled. This sign problem generally leads to an exponential slow down in the time taken by a Monte Carlo algorithm to reach any given level of accuracy, and it has been shown that completely solving the sign problem for an arbitrary quantum system is NP-hard. However, a variety of techniques exist for mitigating the sign problem in specific cases; in particular, the technique of deforming the Monte Carlo simulation's plane of integration onto Lefschetz thimbles (that is, complex hypersurfaces of stationary phase) has seen success for many problems of interest in the context of quantum field theories. We extend this methodology to discrete spin systems by utilizing spin coherent state path integrals to re-express the spin system's partition function in terms of continuous variables. This translation to continuous variables introduces additional challenges into the Lefschetz thimble method, which we address. We show that these techniques do indeed work to lessen the sign problem on some simple spin systems.

1 aMooney, T., C.1 aBringewatt, Jacob1 aBrady, Lucas, T. uhttps://arxiv.org/abs/2110.1069901631nas a2200169 4500008004100000245009500041210006900136260001400205520107500219100001901294700002401313700002101337700002201358700001901380700002501399856003701424 2021 eng d00aLinear and continuous variable spin-wave processing using a cavity-coupled atomic ensemble0 aLinear and continuous variable spinwave processing using a cavit c9/30/20213 a

Spin-wave excitations in ensembles of atoms are gaining attention as a quantum information resource. However, current techniques with atomic spin waves do not achieve universal quantum information processing. We conduct a theoretical analysis of methods to create a high-capacity universal quantum processor and network node using an ensemble of laser-cooled atoms, trapped in a one-dimensional periodic potential and coupled to a ring cavity. We describe how to establish linear quantum processing using a lambda-scheme in a rubidium-atom system, calculate the expected experimental operational fidelities. Second, we derive an efficient method to achieve linear controllability with a single ensemble of atoms, rather than two-ensembles as proposed in [K. C. Cox et al. Spin-Wave Quantum Computing with Atoms in a Single-Mode Cavity, preprint 2021]. Finally, we propose to use the spin-wave processor for continuous-variable quantum information processing and present a scheme to generate large dual-rail cluster states useful for deterministic computing. 

1 aCox, Kevin, C.1 aBienias, Przemyslaw1 aMeyer, David, H.1 aFahey, Donald, P.1 aKunz, Paul, D.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2109.1524601677nas a2200181 4500008004100000022001400041245010400055210006900159260001500228490000700243520109900250100001901349700002001368700001801388700002401406700002801430856003701458 2021 eng d a2045-232200aMachine learning outperforms thermodynamics in measuring how well a many-body system learns a drive0 aMachine learning outperforms thermodynamics in measuring how wel c10/22/20210 v113 a

Diverse many-body systems, from soap bubbles to suspensions to polymers, learn and remember patterns in the drives that push them far from equilibrium. This learning may be leveraged for computation, memory, and engineering. Until now, many-body learning has been detected with thermodynamic properties, such as work absorption and strain. We progress beyond these macroscopic properties first defined for equilibrium contexts: We quantify statistical mechanical learning using representation learning, a machine-learning model in which information squeezes through a bottleneck. By calculating properties of the bottleneck, we measure four facets of many-body systems' learning: classification ability, memory capacity, discrimination ability, and novelty detection. Numerical simulations of a classical spin glass illustrate our technique. This toolkit exposes self-organization that eludes detection by thermodynamic measures: Our toolkit more reliably and more precisely detects and quantifies learning by matter while providing a unifying framework for many-body learning. 

1 aZhong, Weishun1 aGold, Jacob, M.1 aMarzen, Sarah1 aEngland, Jeremy, L.1 aHalpern, Nicole, Yunger uhttps://arxiv.org/abs/2004.0360401577nas a2200133 4500008004100000245008200041210006900123260001400192520114500206100001601351700001701367700002201384856003701406 2021 eng d00aThe membership problem for constant-sized quantum correlations is undecidable0 amembership problem for constantsized quantum correlations is und c1/26/20213 a

When two spatially separated parties make measurements on an unknown entangled quantum state, what correlations can they achieve? How difficult is it to determine whether a given correlation is a quantum correlation? These questions are central to problems in quantum communication and computation. Previous work has shown that the general membership problem for quantum correlations is computationally undecidable. In the current work we show something stronger: there is a family of constant-sized correlations -- that is, correlations for which the number of measurements and number of measurement outcomes are fixed -- such that solving the quantum membership problem for this family is computationally impossible. Thus, the undecidability that arises in understanding Bell experiments is not dependent on varying the number of measurements in the experiment. This places strong constraints on the types of descriptions that can be given for quantum correlation sets. Our proof is based on a combination of techniques from quantum self-testing and from undecidability results of the third author for linear system nonlocal games.

1 aFu, Honghao1 aMiller, Carl1 aSlofstra, William uhttps://arxiv.org/abs/2101.1108702079nas a2200133 4500008004100000245007300041210006900114260001400183520164800197100002001845700002701865700001601892856003701908 2021 eng d00aNonlocal Games, Compression Theorems, and the Arithmetical Hierarchy0 aNonlocal Games Compression Theorems and the Arithmetical Hierarc c10/9/20213 a

We investigate the connection between the complexity of nonlocal games and the arithmetical hierarchy, a classification of languages according to the complexity of arithmetical formulas defining them. It was recently shown by Ji, Natarajan, Vidick, Wright and Yuen that deciding whether the (finite-dimensional) quantum value of a nonlocal game is 1 or at most 12 is complete for the class Σ1 (i.e., RE). A result of Slofstra implies that deciding whether the commuting operator value of a nonlocal game is equal to 1 is complete for the class Π1 (i.e., coRE). We prove that deciding whether the quantum value of a two-player nonlocal game is exactly equal to 1 is complete for Π2; this class is in the second level of the arithmetical hierarchy and corresponds to formulas of the form "∀x∃yϕ(x,y)". This shows that exactly computing the quantum value is strictly harder than approximating it, and also strictly harder than computing the commuting operator value (either exactly or approximately). We explain how results about the complexity of nonlocal games all follow in a unified manner from a technique known as compression. At the core of our Π2-completeness result is a new "gapless" compression theorem that holds for both quantum and commuting operator strategies. Our compression theorem yields as a byproduct an alternative proof of Slofstra's result that the set of quantum correlations is not closed. We also show how a "gap-preserving" compression theorem for commuting operator strategies would imply that approximating the commuting operator value is complete for Π1.

1 aMousavi, Hamoon1 aNezhadi, Seyed, Sajjad1 aYuen, Henry uhttps://arxiv.org/abs/2110.0465101981nas a2200241 4500008004100000245005400041210005400095260001300149520129500162100002501457700002301482700002001505700002001525700002201545700002201567700001401589700001901603700001801622700001801640700002001658700002401678856003701702 2021 eng d00aObservation of a prethermal discrete time crystal0 aObservation of a prethermal discrete time crystal c2/2/20213 a

The conventional framework for defining and understanding phases of matter requires thermodynamic equilibrium. Extensions to non-equilibrium systems have led to surprising insights into the nature of many-body thermalization and the discovery of novel phases of matter, often catalyzed by driving the system periodically. The inherent heating from such Floquet drives can be tempered by including strong disorder in the system, but this can also mask the generality of non-equilibrium phases. In this work, we utilize a trapped-ion quantum simulator to observe signatures of a non-equilibrium driven phase without disorder: the prethermal discrete time crystal (PDTC). Here, many-body heating is suppressed not by disorder-induced many-body localization, but instead via high-frequency driving, leading to an expansive time window where non-equilibrium phases can emerge. We observe a number of key features that distinguish the PDTC from its many-body-localized disordered counterpart, such as the drive-frequency control of its lifetime and the dependence of time-crystalline order on the energy density of the initial state. Floquet prethermalization is thus presented as a general strategy for creating, stabilizing and studying intrinsically out-of-equilibrium phases of matter.

1 aKyprianidis, Antonis1 aMachado, Francisco1 aMorong, William1 aBecker, Patrick1 aCollins, Kate, S.1 aElse, Dominic, V.1 aFeng, Lei1 aHess, Paul, W.1 aNayak, Chetan1 aPagano, Guido1 aYao, Norman, Y.1 aMonroe, Christopher uhttps://arxiv.org/abs/2102.0169501625nas a2200229 4500008004100000245008800041210006900129260001400198520092400212100001801136700002101154700001601175700002101191700001601212700002201228700001801250700002501268700002101293700002001314700002401334856003701358 2021 eng d00aObservation of measurement-induced quantum phases in a trapped-ion quantum computer0 aObservation of measurementinduced quantum phases in a trappedion c6/10/20213 a

Many-body open quantum systems balance internal dynamics against decoherence from interactions with an environment. Here, we explore this balance via random quantum circuits implemented on a trapped ion quantum computer, where the system evolution is represented by unitary gates with interspersed projective measurements. As the measurement rate is varied, a purification phase transition is predicted to emerge at a critical point akin to a fault-tolerent threshold. We probe the "pure" phase, where the system is rapidly projected to a deterministic state conditioned on the measurement outcomes, and the "mixed" or "coding" phase, where the initial state becomes partially encoded into a quantum error correcting codespace. We find convincing evidence of the two phases and show numerically that, with modest system scaling, critical properties of the transition clearly emerge.

1 aNoel, Crystal1 aNiroula, Pradeep1 aZhu, Daiwei1 aRisinger, Andrew1 aEgan, Laird1 aBiswas, Debopriyo1 aCetina, Marko1 aGorshkov, Alexey, V.1 aGullans, Michael1 aHuse, David, A.1 aMonroe, Christopher uhttps://arxiv.org/abs/2106.0588102060nas a2200217 4500008004100000245006500041210006400106260001400170520145900184100001501643700001201658700001501670700002001685700001301705700002001718700001501738700001201753700002501765700001501790856003701805 2021 eng d00aObservation of Stark many-body localization without disorder0 aObservation of Stark manybody localization without disorder c2/14/20213 a

Thermalization is a ubiquitous process of statistical physics, in which details of few-body observables are washed out in favor of a featureless steady state. Even in isolated quantum many-body systems, limited to reversible dynamics, thermalization typically prevails. However, in these systems, there is another possibility: many-body localization (MBL) can result in preservation of a non-thermal state. While disorder has long been considered an essential ingredient for this phenomenon, recent theoretical work has suggested that a quantum many-body system with a uniformly increasing field -- but no disorder -- can also exhibit MBL, resulting in `Stark MBL.' Here we realize Stark MBL in a trapped-ion quantum simulator and demonstrate its key properties: halting of thermalization and slow propagation of correlations. Tailoring the interactions between ionic spins in an effective field gradient, we directly observe their microscopic equilibration for a variety of initial states, and we apply single-site control to measure correlations between separate regions of the spin chain. Further, by engineering a varying gradient, we create a disorder-free system with coexisting long-lived thermalized and nonthermal regions. The results demonstrate the unexpected generality of MBL, with implications about the fundamental requirements for thermalization and with potential uses in engineering long-lived non-equilibrium quantum matter.

1 aMorong, W.1 aLiu, F.1 aBecker, P.1 aCollins, K., S.1 aFeng, L.1 aKyprianidis, A.1 aPagano, G.1 aYou, T.1 aGorshkov, Alexey, V.1 aMonroe, C. uhttps://arxiv.org/abs/2102.0725001362nas a2200193 4500008004100000022001400041245013800055210006900193260001400262490000800276520071000284100001900994700002101013700002401034700002401058700002301082700002601105856003701131 2021 eng d a2469-993400aQuantum circuits for the realization of equivalent forms of one-dimensional discrete-time quantum walks on near-term quantum hardware0 aQuantum circuits for the realization of equivalent forms of oned c12/8/20210 v1043 a

Quantum walks are a promising framework for developing quantum algorithms and quantum simulations. They represent an important test case for the application of quantum computers. Here we present different forms of discrete-time quantum walks (DTQWs) and show their equivalence for physical realizations. Using an appropriate digital mapping of the position space on which a walker evolves to the multiqubit states of a quantum processor, we present different configurations of quantum circuits for the implementation of DTQWs in one-dimensional position space. We provide example circuits for a five-qubit processor and address scalability to higher dimensions as well as larger quantum processors.

1 aSingh, Shivani1 aAlderete, Huerta1 aBalu, Radhakrishnan1 aMonroe, Christopher1 aLinke, Norbert, M.1 aChandrashekar, C., M. uhttps://arxiv.org/abs/2001.1119702003nas a2200253 4500008004100000245008100041210006900122260001400191520125700205100002301462700001801485700002001503700002101523700002001544700002001564700001701584700002101601700001401622700001701636700002401653700002001677700001501697856003701712 2021 eng d00aQuantum Computational Supremacy via High-Dimensional Gaussian Boson Sampling0 aQuantum Computational Supremacy via HighDimensional Gaussian Bos c2/24/20213 a

Photonics is a promising platform for demonstrating quantum computational supremacy (QCS) by convincingly outperforming the most powerful classical supercomputers on a well-defined computational task. Despite this promise, existing photonics proposals and demonstrations face significant hurdles. Experimentally, current implementations of Gaussian boson sampling lack programmability or have prohibitive loss rates. Theoretically, there is a comparative lack of rigorous evidence for the classical hardness of GBS. In this work, we make significant progress in improving both the theoretical evidence and experimental prospects. On the theory side, we provide strong evidence for the hardness of Gaussian boson sampling, placing it on par with the strongest theoretical proposals for QCS. On the experimental side, we propose a new QCS architecture, high-dimensional Gaussian boson sampling, which is programmable and can be implemented with low loss rates using few optical components. We show that particular classical algorithms for simulating GBS are vastly outperformed by high-dimensional Gaussian boson sampling experiments at modest system sizes. This work thus opens the path to demonstrating QCS with programmable photonic processors.

1 aDeshpande, Abhinav1 aMehta, Arthur1 aVincent, Trevor1 aQuesada, Nicolas1 aHinsche, Marcel1 aIoannou, Marios1 aMadsen, Lars1 aLavoie, Jonathan1 aQi, Haoyu1 aEisert, Jens1 aHangleiter, Dominik1 aFefferman, Bill1 aDhand, Ish uhttps://arxiv.org/abs/2102.1247401237nas a2200253 4500008004100000245004100041210004100082260001300123520055200136100001900688700002400707700002100731700002000752700002700772700001800799700001600817700001700833700002000850700002100870700001900891700001300910700002300923856003700946 2021 eng d00aQuantum Machine Learning for Finance0 aQuantum Machine Learning for Finance c9/9/20213 a

Quantum computers are expected to surpass the computational capabilities of classical computers during this decade, and achieve disruptive impact on numerous industry sectors, particularly finance. In fact, finance is estimated to be the first industry sector to benefit from Quantum Computing not only in the medium and long terms, but even in the short term. This review paper presents the state of the art of quantum algorithms for financial applications, with particular focus to those use cases that can be solved via Machine Learning.

1 aPistoia, Marco1 aAhmad, Syed, Farhan1 aAjagekar, Akshay1 aButs, Alexander1 aChakrabarti, Shouvanik1 aHerman, Dylan1 aHu, Shaohan1 aJena, Andrew1 aMinssen, Pierre1 aNiroula, Pradeep1 aRattew, Arthur1 aSun, Yue1 aYalovetzky, Romina uhttps://arxiv.org/abs/2109.0429801351nas a2200193 4500008004100000245011700041210006900158260001400227300000800241490000600249520075900255100001301014700001701027700001801044700002201062700002001084700001601104856003701120 2021 eng d00aQuantum-accelerated multilevel Monte Carlo methods for stochastic differential equations in mathematical finance0 aQuantumaccelerated multilevel Monte Carlo methods for stochastic c6/22/2021 a4810 v53 a

Inspired by recent progress in quantum algorithms for ordinary and partial differential equations, we study quantum algorithms for stochastic differential equations (SDEs). Firstly we provide a quantum algorithm that gives a quadratic speed-up for multilevel Monte Carlo methods in a general setting. As applications, we apply it to compute expection values determined by classical solutions of SDEs, with improved dependence on precision. We demonstrate the use of this algorithm in a variety of applications arising in mathematical finance, such as the Black-Scholes and Local Volatility models, and Greeks. We also provide a quantum algorithm based on sublinear binomial sampling for the binomial option pricing model with the same improvement.

1 aAn, Dong1 aLinden, Noah1 aLiu, Jin-Peng1 aMontanaro, Ashley1 aShao, Changpeng1 aWang, Jiasu uhttps://arxiv.org/abs/2012.0628302275nas a2200193 4500008004100000245007200041210006900113260001500182490000600197520168200203100002401885700002101909700002601930700002301956700002301979700002302002700001902025856003702044 2021 eng d00aRay-based framework for state identification in quantum dot devices0 aRaybased framework for state identification in quantum dot devic c06/17/20210 v23 a

Quantum dots (QDs) defined with electrostatic gates are a leading platform for a scalable quantum computing implementation. However, with increasing numbers of qubits, the complexity of the control parameter space also grows. Traditional measurement techniques, relying on complete or near-complete exploration via two-parameter scans (images) of the device response, quickly become impractical with increasing numbers of gates. Here, we propose to circumvent this challenge by introducing a measurement technique relying on one-dimensional projections of the device response in the multi-dimensional parameter space. Dubbed as the ray-based classification (RBC) framework, we use this machine learning (ML) approach to implement a classifier for QD states, enabling automated recognition of qubit-relevant parameter regimes. We show that RBC surpasses the 82 % accuracy benchmark from the experimental implementation of image-based classification techniques from prior work while cutting down the number of measurement points needed by up to 70 %. The reduction in measurement cost is a significant gain for time-intensive QD measurements and is a step forward towards the scalability of these devices. We also discuss how the RBC-based optimizer, which tunes the device to a multi-qubit regime, performs when tuning in the two- and three-dimensional parameter spaces defined by plunger and barrier gates that control the dots. This work provides experimental validation of both efficient state identification and optimization with ML techniques for non-traditional measurements in quantum systems with high-dimensional parameter spaces and time-intensive measurements.

1 aZwolak, Justyna, P.1 aMcJunkin, Thomas1 aKalantre, Sandesh, S.1 aNeyens, Samuel, F.1 aMacQuarrie, E., R.1 aEriksson, Mark, A.1 aTaylor, J., M. uhttps://arxiv.org/abs/2102.1178401694nas a2200169 4500008004100000245004400041210004400085260001500129520120900144100002801353700002801381700002101409700002001430700001701450700002001467856003701487 2021 eng d00aResource theory of quantum uncomplexity0 aResource theory of quantum uncomplexity c10/21/20213 a

Quantum complexity is emerging as a key property of many-body systems, including black holes, topological materials, and early quantum computers. A state's complexity quantifies the number of computational gates required to prepare the state from a simple tensor product. The greater a state's distance from maximal complexity, or ``uncomplexity,'' the more useful the state is as input to a quantum computation. Separately, resource theories -- simple models for agents subject to constraints -- are burgeoning in quantum information theory. We unite the two domains, confirming Brown and Susskind's conjecture that a resource theory of uncomplexity can be defined. The allowed operations, fuzzy operations, are slightly random implementations of two-qubit gates chosen by an agent. We formalize two operational tasks, uncomplexity extraction and expenditure. Their optimal efficiencies depend on an entropy that we engineer to reflect complexity. We also present two monotones, uncomplexity measures that decline monotonically under fuzzy operations, in certain regimes. This work unleashes on many-body complexity the resource-theory toolkit from quantum information theory.

1 aHalpern, Nicole, Yunger1 aKothakonda, Naga, B. T.1 aHaferkamp, Jonas1 aMunson, Anthony1 aEisert, Jens1 aFaist, Philippe uhttps://arxiv.org/abs/2110.1137102193nas a2200157 4500008004100000245010400041210006900145260001400214490000600228520169000234100001901924700001301943700002401956700001801980856003701998 2021 eng d00aResource-Optimized Fermionic Local-Hamiltonian Simulation on Quantum Computer for Quantum Chemistry0 aResourceOptimized Fermionic LocalHamiltonian Simulation on Quant c7/21/20210 v53 a

The ability to simulate a fermionic system on a quantum computer is expected to revolutionize chemical engineering, materials design, nuclear physics, to name a few. Thus, optimizing the simulation circuits is of significance in harnessing the power of quantum computers. Here, we address this problem in two aspects. In the fault-tolerant regime, we optimize the $\rzgate$ and $\tgate$ gate counts along with the ancilla qubit counts required, assuming the use of a product-formula algorithm for implementation. We obtain a savings ratio of two in the gate counts and a savings ratio of eleven in the number of ancilla qubits required over the state of the art. In the pre-fault tolerant regime, we optimize the two-qubit gate counts, assuming the use of the variational quantum eigensolver (VQE) approach. Specific to the latter, we present a framework that enables bootstrapping the VQE progression towards the convergence of the ground-state energy of the fermionic system. This framework, based on perturbation theory, is capable of improving the energy estimate at each cycle of the VQE progression, by about a factor of three closer to the known ground-state energy compared to the standard VQE approach in the test-bed, classically-accessible system of the water molecule. The improved energy estimate in turn results in a commensurate level of savings of quantum resources, such as the number of qubits and quantum gates, required to be within a pre-specified tolerance from the known ground-state energy. We also explore a suite of generalized transformations of fermion to qubit operators and show that resource-requirement savings of up to more than 20% is possible.

1 aWang, Qingfeng1 aLi, Ming1 aMonroe, Christopher1 aNam, Yunseong uhttps://arxiv.org/abs/2004.0415101423nas a2200145 4500008004100000245005800041210005300099260001400152520098400166100001801150700003701168700001601205700001901221856003701240 2021 eng d00aRPPLNS: Pay-per-last-N-shares with a Randomised Twist0 aRPPLNS PayperlastNshares with a Randomised Twist c2/15/20213 a

"Pay-per-last-N-shares" (PPLNS) is one of the most common payout strategies used by mining pools in Proof-of-Work (PoW) cryptocurrencies. As with any payment scheme, it is imperative to study issues of incentive compatibility of miners within the pool. For PPLNS this question has only been partially answered; we know that reasonably-sized miners within a PPLNS pool prefer following the pool protocol over employing specific deviations. In this paper, we present a novel modification to PPLNS where we randomise the protocol in a natural way. We call our protocol "Randomised pay-per-last-N-shares" (RPPLNS), and note that the randomised structure of the protocol greatly simplifies the study of its incentive compatibility. We show that RPPLNS maintains the strengths of PPLNS (i.e., fairness, variance reduction, and resistance to pool hopping), while also being robust against a richer class of strategic mining than what has been shown for PPLNS.

1 aLazos, Philip1 aMarmolejo-Cossío, Francisco, J.1 aZhou, Xinyu1 aKatz, Jonathan uhttps://arxiv.org/abs/2102.0768101834nas a2200157 4500008004100000245007600041210006900117260001400186520133100200100002901531700001601560700002501576700002101601700001701622856003701639 2021 eng d00aSingularities in nearly-uniform 1D condensates due to quantum diffusion0 aSingularities in nearlyuniform 1D condensates due to quantum dif c3/10/20213 a

Dissipative systems can often exhibit wavelength-dependent loss rates. One prominent example is Rydberg polaritons formed by electromagnetically-induced transparency, which have long been a leading candidate for studying the physics of interacting photons and also hold promise as a platform for quantum information. In this system, dissipation is in the form of quantum diffusion, i.e., proportional to k2 (k being the wavevector) and vanishing at long wavelengths as k→0. Here, we show that one-dimensional condensates subject to this type of loss are unstable to long-wavelength density fluctuations in an unusual manner: after a prolonged period in which the condensate appears to relax to a uniform state, local depleted regions quickly form and spread ballistically throughout the system. We connect this behavior to the leading-order equation for the nearly-uniform condensate -- a dispersive analogue to the Kardar-Parisi-Zhang (KPZ) equation -- which develops singularities in finite time. Furthermore, we show that the wavefronts of the depleted regions are described by purely dissipative solitons within a pair of hydrodynamic equations, with no counterpart in lossless condensates. We close by discussing conditions under which such singularities and the resulting solitons can be physically realized.

1 aBaldwin, Christopher, L.1 aBienias, P.1 aGorshkov, Alexey, V.1 aGullans, Michael1 aMaghrebi, M. uhttps://arxiv.org/abs/2103.0629301130nas a2200169 4500008004100000245006700041210006500108260001400173520060600187100001900793700002400812700002100836700001900857700002200876700002500898856003700923 2021 eng d00aSpin-Wave Quantum Computing with Atoms in a Single-Mode Cavity0 aSpinWave Quantum Computing with Atoms in a SingleMode Cavity c9/30/20213 a

We present a method for network-capable quantum computing that relies on holographic spin-wave excitations stored collectively in ensembles of qubits. We construct an orthogonal basis of spin waves in a one-dimensional array and show that high-fidelity universal linear controllability can be achieved using only phase shifts, applied in both momentum and position space. Neither single-site addressability nor high single-qubit cooperativity is required, and the spin waves can be read out with high efficiency into a single cavity mode for quantum computing and networking applications. 

1 aCox, Kevin, C.1 aBienias, Przemyslaw1 aMeyer, David, H.1 aKunz, Paul, D.1 aFahey, Donald, P.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2109.1525201359nas a2200157 4500008004100000245003200041210003200073260001400105520093200119100002001051700002001071700002701091700002201118700002401140856003701164 2021 eng d00aSynchronous Values of Games0 aSynchronous Values of Games c9/29/20213 a

We study synchronous values of games, especially synchronous games. It is known that a synchronous game has a perfect strategy if and only if it has a perfect synchronous strategy. However, we give examples of synchronous games, in particular graph colouring games, with synchronous value that is strictly smaller than their ordinary value. Thus, the optimal strategy for a synchronous game need not be synchronous. We derive a formula for the synchronous value of an XOR game as an optimization problem over a spectrahedron involving a matrix related to the cost matrix. We give an example of a game such that the synchronous value of repeated products of the game is strictly increasing. We show that the synchronous quantum bias of the XOR of two XOR games is not multiplicative. Finally, we derive geometric and algebraic conditions that a set of projections that yields the synchronous value of a game must satisfy.

1 aHelton, William1 aMousavi, Hamoon1 aNezhadi, Seyed, Sajjad1 aPaulsen, Vern, I.1 aRussell, Travis, B. uhttps://arxiv.org/abs/2109.1474101340nas a2200133 4500008004100000245006500041210006500106260001400171520092300185100001901108700002001127700002201147856003701169 2021 eng d00aTesting quantum gravity with interactive information sensing0 aTesting quantum gravity with interactive information sensing c1/27/20213 a

We suggest a test of a central prediction of perturbatively quantized general relativity: the coherent communication of quantum information between massive objects through gravity. To do this, we introduce the concept of interactive quantum information sensing, a protocol tailored to the verification of dynamical entanglement generation between a pair of systems. Concretely, we propose to monitor the periodic wavefunction collapse and revival in an atomic interferometer which is gravitationally coupled to a mechanical oscillator. We prove a theorem which shows that, under the assumption of time-translation invariance, this collapse and revival is possible if and only if the gravitational interaction forms an entangling channel. Remarkably, as this approach improves at moderate temperatures and relies primarily upon atomic coherence, our numerical estimates indicate feasibility with current devices.

1 aCarney, Daniel1 aMüller, Holger1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2101.1162901551nas a2200181 4500008004100000245006000041210005800101300000800159490000600167520101600173100002701189700002401216700002301240700002701263700002001290700002201310856003701332 2021 eng d00aA Threshold for Quantum Advantage in Derivative Pricing0 aThreshold for Quantum Advantage in Derivative Pricing a4630 v53 a

We give an upper bound on the resources required for valuable quantum advantage in pricing derivatives. To do so, we give the first complete resource estimates for useful quantum derivative pricing, using autocallable and Target Accrual Redemption Forward (TARF) derivatives as benchmark use cases. We uncover blocking challenges in known approaches and introduce a new method for quantum derivative pricing - the re-parameterization method - that avoids them. This method combines pre-trained variational circuits with fault-tolerant quantum computing to dramatically reduce resource requirements. We find that the benchmark use cases we examine require 7.5k logical qubits and a T-depth of 46 million and thus estimate that quantum advantage would require a logical clock speed of 10Mhz. While the resource requirements given here are out of reach of current systems, we hope they will provide a roadmap for further improvements in algorithms, implementations, and planned hardware architectures. 

1 aChakrabarti, Shouvanik1 aKrishnakumar, Rajiv1 aMazzola, Guglielmo1 aStamatopoulos, Nikitas1 aWoerner, Stefan1 aZeng, William, J. uhttps://arxiv.org/abs/2012.0381901337nas a2200157 4500008004100000245005300041210005300094260001300147490000800160520089300168100001901061700002201080700002101102700001901123856003701142 2021 eng d00aTrapped electrons and ions as particle detectors0 aTrapped electrons and ions as particle detectors c8/5/20210 v1273 a

Electrons and ions trapped with electromagnetic fields have long served as important high-precision metrological instruments, and more recently have also been proposed as a platform for quantum information processing. Here we point out that these systems can also be used as highly sensitive detectors of passing charged particles, due to the combination of their extreme charge-to-mass ratio and low-noise quantum readout and control. In particular, these systems can be used to detect energy depositions many orders of magnitude below typical ionization scales. As an illustration, we show that current devices can be used to provide competitive sensitivity to models where ambient dark matter particles carry small electric millicharges ≪e. Our calculations may also be useful in the characterization of noise in quantum computers coming from backgrounds of charged particles.

1 aCarney, Daniel1 aHäffner, Hartmut1 aMoore, David, C.1 aTaylor, J., M. uhttps://arxiv.org/abs/2104.0573701487nas a2200157 4500008004100000022001400041245008000055210006900135260001400204490000600218520099400224100001901218700002001237700002201257856005001279 2021 eng d a2691-339900aUsing an Atom Interferometer to Infer Gravitational Entanglement Generation0 aUsing an Atom Interferometer to Infer Gravitational Entanglement c8/20/20210 v23 a

If gravitational perturbations are quantized into gravitons in analogy with the electromagnetic field and photons, the resulting graviton interactions should lead to an entangling interaction between massive objects. We suggest a test of this prediction. To do this, we introduce the concept of interactive quantum information sensing. This novel sensing protocol is tailored to provable verification of weak dynamical entanglement generation between a pair of systems. We show that this protocol is highly robust to typical thermal noise sources. The sensitivity can moreover be increased both using an initial thermal state and/or an initial phase of entangling via a non-gravitational interaction. We outline a concrete implementation testing the ability of the gravitational field to generate entanglement between an atomic interferometer and mechanical oscillator. Preliminary numerical estimates suggest that near-term devices could feasibly be used to perform the experiment.

1 aCarney, Daniel1 aMüller, Holger1 aTaylor, Jacob, M. uhttp://dx.doi.org/10.1103/PRXQuantum.2.03033001345nas a2200145 4500008004100000245006600041210006200107260001400169490000600183520092300189100001801112700001301130700001901143856003701162 2020 eng d00aApproximate Quantum Fourier Transform with O(nlog(n)) T gates0 aApproximate Quantum Fourier Transform with Onlogn T gates c3/13/20200 v63 a

The ability to implement the Quantum Fourier Transform (QFT) efficiently on a quantum computer enables the advantages offered by a variety of fundamental quantum algorithms, such as those for integer factoring, computing discrete logarithm over Abelian groups, and phase estimation. The standard fault-tolerant implementation of an n-qubit QFT approximates the desired transformation by removing small-angle controlled rotations and synthesizing the remaining ones into Clifford+t gates, incurring the t-count complexity of O(n log2 (n)). In this paper we show how to obtain approximate QFT with the t-count of O(n log(n)). Our approach relies on quantum circuits with measurements and feedforward, and on reusing a special quantum state that induces the phase gradient transformation. We report asymptotic analysis as well as concrete circuits, demonstrating significant advantages in both theory and practice.

1 aNam, Yunseong1 aSu, Yuan1 aMaslov, Dmitri uhttps://arxiv.org/abs/1803.0493302481nas a2200229 4500008004100000245006800041210006700109260001300176490000700189520180000196100002401996700002102020700002602041700001902067700002302086700001902109700002002128700002402148700002302172700001902195856003702214 2020 eng d00aAuto-tuning of double dot devices in situ with machine learning0 aAutotuning of double dot devices in situ with machine learning c4/1/20200 v133 a

There are myriad quantum computing approaches, each having its own set of challenges to understand and effectively control their operation. Electrons confined in arrays of semiconductor nanostructures, called quantum dots (QDs), is one such approach. The easy access to control parameters, fast measurements, long qubit lifetimes, and the potential for scalability make QDs especially attractive. However, as the size of the QD array grows, so does the number of parameters needed for control and thus the tuning complexity. The current practice of manually tuning the qubits is a relatively time-consuming procedure and is inherently impractical for scaling up and applications. In this work, we report on the in situ implementation of an auto-tuning protocol proposed by Kalantre et al. [arXiv:1712.04914]. In particular, we discuss how to establish a seamless communication protocol between a machine learning (ML)-based auto-tuner and the experimental apparatus. We then show that a ML algorithm trained exclusively on synthetic data coming from a physical model to quantitatively classify the state of the QD device, combined with an optimization routine, can be used to replace manual tuning of gate voltages in devices. A success rate of over 85 % is determined for tuning to a double quantum dot regime when at least one of the plunger gates is initiated sufficiently close to the desired state. Modifications to the training network, fitness function, and optimizer are discussed as a path towards further improvement in the success rate when starting both near and far detuned from the target double dot range.

1 aZwolak, Justyna, P.1 aMcJunkin, Thomas1 aKalantre, Sandesh, S.1 aDodson, J., P.1 aMacQuarrie, E., R.1 aSavage, D., E.1 aLagally, M., G.1 aCoppersmith, S., N.1 aEriksson, Mark, A.1 aTaylor, J., M. uhttps://arxiv.org/abs/1909.0803001526nas a2200133 4500008004100000245011300041210006900154260001400223520105400237100002001291700002001311700002401331856003701355 2020 eng d00aThe Character of Motional Modes for Entanglement and Sympathetic Cooling of Mixed-Species Trapped Ion Chains0 aCharacter of Motional Modes for Entanglement and Sympathetic Coo c4/16/20203 a

Modular mixed-species ion-trap networks are a promising framework for scalable quantum information processing, where one species acts as a memory qubit and another as a communication qubit. This architecture requires high-fidelity mixed-species entangling gates to transfer information from communication to memory qubits through their collective motion. We investigate the character of the motional modes of a mixed-species ion chain for entangling operations and also sympathetic cooling. We find that the laser power required for high-fidelity entangling gates based on transverse modes is at least an order of magnitude higher than that based on axial modes for widely different masses of the two species. We also find that for even moderate mass differences, the transverse modes are much harder to cool than the axial modes regardless of the ion chain configuration. Therefore, transverse modes conventionally used for operations in single-species ion chains may not be well suited for mixed-species chains with widely different masses.

1 aSosnova, Ksenia1 aCarter, Allison1 aMonroe, Christopher uhttps://arxiv.org/abs/2004.0804501669nas a2200181 4500008004100000245010700041210006900148260001300217490000800230520098500238100002701223700002201250700002201272700002401294700001901318700001901337856013101356 2020 eng d00aCollisions of room-temperature helium with ultracold lithium and the van der Waals bound state of HeLi0 aCollisions of roomtemperature helium with ultracold lithium and  c1/6/20200 v1013 a

We have computed the thermally averaged total, elastic rate coefficient for the collision of a room-temperature helium atom with an ultracold lithium atom. This rate coefficient has been computed as part of the characterization of a cold-atom vacuum sensor based on laser-cooled Li 6 or Li 7 atoms that will operate in the ultrahigh-vacuum (p< 10− 6 Pa) and extreme-high-vacuum (p< 10− 10 Pa) regimes. The analysis involves computing the X 2 Σ+ HeLi Born-Oppenheimer potential followed by the numerical solution of the relevant radial Schrödinger equation. The potential is computed using a single-reference-coupled-cluster electronic-structure method with basis sets of different completeness in order to characterize our uncertainty budget. We predict that the rate coefficient for a 300 K helium gas and a 1 μ K Li gas is 1.467 (13)× 10− 9 cm 3/s for He 4+ Li 6 and 1.471 (13)× 10− 9 cm 3/s for He 4+ Li 7, where the …

1 aMakrides, Constantinos1 aBarker, Daniel, S1 aFedchak, James, A1 aScherschligt, Julia1 aEckel, Stephen1 aTiesinga, Eite uhttps://www.quics.umd.edu/publications/collisions-room-temperature-helium-ultracold-lithium-and-van-der-waals-bound-state-heli01895nas a2200121 4500008004100000245009500041210006900136260001400205520147700219100002101696700001901717856003701736 2020 eng d00aComputations with Greater Quantum Depth Are Strictly More Powerful (Relative to an Oracle)0 aComputations with Greater Quantum Depth Are Strictly More Powerf c4/23/20203 a

A conjecture of Jozsa [Jozsa06] states that any polynomial-time quantum computation can be simulated by polylogarithmic-depth quantum computation interleaved with polynomial-depth classical computation. Separately, Aaronson [Aaronson05, Aaronson11, Aaronson14] conjectured that there exists an oracle O such that BQPO≠(BPPBQNC)O. These conjectures are intriguing allusions to the unresolved potential of combining classical and low-depth quantum computation. In this work we show that the Welded Tree Problem, which is an oracle problem that can be solved in quantum polynomial time as shown by Childs et al. [ChildsCDFGS03], cannot be solved in BPPBQNC, nor can it be solved in the class that Jozsa describes. This proves Aaronson's oracle separation conjecture and provides a counterpoint to Jozsa's conjecture relative to the Welded Tree oracle problem. More precisely, we define two complexity classes, HQC and JC whose languages are decided by two different families of interleaved quantum-classical circuits. HQC contains BPPBQNC and is therefore relevant to Aaronson's conjecture, while JC captures the model of computation that Jozsa considers. We show that the Welded Tree Problem gives an oracle separation between either of {JC,HQC} and BQP. Therefore, even when interleaved with arbitrary polynomial-time classical computation, greater "quantum depth" leads to strictly greater computational ability in this relativized setting.

1 aCoudron, Matthew1 aMenda, Sanketh uhttps://arxiv.org/abs/1909.1050301342nas a2200169 4500008004100000245007000041210006900111260001400180520083000194100002201024700001301046700002001059700001801079700001701097700002101114856003701135 2020 eng d00aConfronting lattice parton distributions with global QCD analysis0 aConfronting lattice parton distributions with global QCD analysi c10/1/20203 a

We present the first Monte Carlo based global QCD analysis of spin-averaged and spin-dependent parton distribution functions (PDFs) that includes nucleon isovector matrix elements in coordinate space from lattice QCD. We investigate the degree of universality of the extracted PDFs when the lattice and experimental data are treated under the same conditions within the Bayesian likelihood analysis. For the unpolarized sector, we find rather weak constraints from the current lattice data on the phenomenological PDFs, and difficulties in describing the lattice matrix elements at large spatial distances. In contrast, for the polarized PDFs we find good agreement between experiment and lattice data, with the latter providing significant constraints on the spin-dependent isovector quark and antiquark distributions

1 aBringewatt, Jacob1 aSato, N.1 aMelnitchouk, W.1 aQiu, Jian-Wei1 aSteffens, F.1 aConstantinou, M. uhttps://arxiv.org/abs/2010.0054801932nas a2200181 4500008004100000245005700041210005700098260001300155520138000168100002501548700002001573700002201593700002701615700002301642700002501665700002301690856003701713 2020 eng d00aCritical Theory for the Breakdown of Photon Blockade0 aCritical Theory for the Breakdown of Photon Blockade c6/9/20203 a

Photon blockade is the result of the interplay between the quantized nature of light and strong optical nonlinearities, whereby strong photon-photon repulsion prevents a quantum optical system from absorbing multiple photons. We theoretically study a single atom coupled to the light field, described by the resonantly driven Jaynes--Cummings model, in which case the photon blockade breaks down in a second order phase transition at a critical drive strength. We show that this transition is associated to the spontaneous breaking of an anti-unitary PT-symmetry. Within a semiclassical approximation we calculate the expectation values of observables in the steady state. We then move beyond the semiclassical approximation and approach the critical point from the disordered (blockaded) phase by reducing the Lindblad quantum master equation to a classical rate equation that we solve. The width of the steady-state distribution in Fock space is found to diverge as we approach the critical point with a simple power-law, allowing us to calculate the critical scaling of steady state observables without invoking mean-field theory. We propose a simple physical toy model for biased diffusion in the space of occupation numbers, which captures the universal properties of the steady state. We list several experimental platforms where this phenomenon may be observed.

1 aCurtis, Jonathan, B.1 aBoettcher, Igor1 aYoung, Jeremy, T.1 aMaghrebi, Mohammad, F.1 aCarmichael, Howard1 aGorshkov, Alexey, V.1 aFoss-Feig, Michael uhttps://arxiv.org/abs/2006.0559301563nas a2200169 4500008004100000245002700041210002700068260001400095300001200109490000700121520114400128100002201272700002401294700001801318700002001336856003701356 2020 eng d00aDiscrete Time Crystals0 aDiscrete Time Crystals c3/10/2020 a467-4990 v113 a

Experimental advances have allowed for the exploration of nearly isolated quantum many-body systems whose coupling to an external bath is very weak. A particularly interesting class of such systems is those which do not thermalize under their own isolated quantum dynamics. In this review, we highlight the possibility for such systems to exhibit new non-equilibrium phases of matter. In particular, we focus on "discrete time crystals", which are many-body phases of matter characterized by a spontaneously broken discrete time translation symmetry. We give a definition of discrete time crystals from several points of view, emphasizing that they are a non-equilibrium phenomenon, which is stabilized by many-body interactions, with no analog in non-interacting systems. We explain the theory behind several proposed models of discrete time crystals, and compare a number of recent realizations, in different experimental contexts. 

1 aElse, Dominic, V.1 aMonroe, Christopher1 aNayak, Chetan1 aYao, Norman, Y. uhttps://arxiv.org/abs/1905.1323201905nas a2200157 4500008004100000245006300041210006300104260001300167300001200180490001000192520138200202100001901584700002201603700002301625856009901648 2020 eng d00aEfficient Simulation of Random States and Random Unitaries0 aEfficient Simulation of Random States and Random Unitaries c5/1/2020 a759-7870 v121073 a

We consider the problem of efficiently simulating random quantum states and random unitary operators, in a manner which is convincing to unbounded adversaries with black-box oracle access.

This problem has previously only been considered for restricted adversaries. Against adversaries with an a priori bound on the number of queries, it is well-known that t-designs suffice. Against polynomial-time adversaries, one can use pseudorandom states (PRS) and pseudorandom unitaries (PRU), as defined in a recent work of Ji, Liu, and Song; unfortunately, no provably secure construction is known for PRUs.

In our setting, we are concerned with unbounded adversaries. Nonetheless, we are able to give stateful quantum algorithms which simulate the ideal object in both settings of interest. In the case of Haar-random states, our simulator is polynomial-time, has negligible error, and can also simulate verification and reflection through the simulated state. This yields an immediate application to quantum money: a money scheme which is information-theoretically unforgeable and untraceable. In the case of Haar-random unitaries, our simulator takes polynomial space, but simulates both forward and inverse access with zero error.

These results can be seen as the first significant steps in developing a theory of lazy sampling for random quantum objects.

1 aAlagic, Gorjan1 aMajenz, Christian1 aRussell, Alexander uhttps://www.quics.umd.edu/publications/efficient-simulation-random-states-and-random-unitaries01465nas a2200265 4500008004100000245006700041210006500108260001500173490000800188520070100196100001800897700002200915700002500937700002400962700002500986700001801011700002101029700002001050700002501070700001601095700001701111700001501128700001901143856003701162 2020 eng d00aExperimental Low-Latency Device-Independent Quantum Randomness0 aExperimental LowLatency DeviceIndependent Quantum Randomness c12/24/20190 v1243 a

Applications of randomness such as private key generation and public randomness beacons require small blocks of certified random bits on demand. Device-independent quantum random number generators can produce such random bits, but existing quantum-proof protocols and loophole-free implementations suffer from high latency, requiring many hours to produce any random bits. We demonstrate device-independent quantum randomness generation from a loophole-free Bell test with a more efficient quantum-proof protocol, obtaining multiple blocks of 512 bits with an average experiment time of less than 5 min per block and with certified error bounded by 2−64≈5.42×10−20.

1 aZhang, Yanbao1 aShalm, Lynden, K.1 aBienfang, Joshua, C.1 aStevens, Martin, J.1 aMazurek, Michael, D.1 aNam, Sae, Woo1 aAbellán, Carlos1 aAmaya, Waldimar1 aMitchell, Morgan, W.1 aFu, Honghao1 aMiller, Carl1 aMink, Alan1 aKnill, Emanuel uhttps://arxiv.org/abs/1812.0778602128nas a2200229 4500008004100000245006400041210006200105260001400167520146400181100001601645700002301661700001801684700002101702700001601723700002201739700002001761700001501781700002301796700001801819700002401837856003701861 2020 eng d00aFault-Tolerant Operation of a Quantum Error-Correction Code0 aFaultTolerant Operation of a Quantum ErrorCorrection Code c9/24/20203 a

Quantum error correction protects fragile quantum information by encoding it in a larger quantum system whose extra degrees of freedom enable the detection and correction of errors. An encoded logical qubit thus carries increased complexity compared to a bare physical qubit. Fault-tolerant protocols contain the spread of errors and are essential for realizing error suppression with an error-corrected logical qubit. Here we experimentally demonstrate fault-tolerant preparation, rotation, error syndrome extraction, and measurement on a logical qubit encoded in the 9-qubit Bacon-Shor code. For the logical qubit, we measure an average fault-tolerant preparation and measurement error of 0.6% and a transversal Clifford gate with an error of 0.3% after error correction. The result is an encoded logical qubit whose logical fidelity exceeds the fidelity of the entangling operations used to create it. We compare these operations with non-fault-tolerant protocols capable of generating arbitrary logical states, and observe the expected increase in error. We directly measure the four Bacon-Shor stabilizer generators and are able to detect single qubit Pauli errors. These results show that fault-tolerant quantum systems are currently capable of logical primitives with error rates lower than their constituent parts. With the future addition of intermediate measurements, the full power of scalable quantum error-correction can be achieved. 

1 aEgan, Laird1 aDebroy, Dripto, M.1 aNoel, Crystal1 aRisinger, Andrew1 aZhu, Daiwei1 aBiswas, Debopriyo1 aNewman, Michael1 aLi, Muyuan1 aBrown, Kenneth, R.1 aCetina, Marko1 aMonroe, Christopher uhttps://arxiv.org/abs/2009.1148201231nas a2200121 4500008004100000245006200041210005800103260001100161300001200172520081200184100001700996856009601013 2020 eng d00aThe impossibility of efficient quantum weak coin flipping0 aimpossibility of efficient quantum weak coin flipping c6/2020 a916-9293 a

How can two parties with competing interests carry out a fair coin flip across a quantum communication channel? This problem (quantum weak coin-flipping) was formalized more than 15 years ago, and, despite some phenomenal theoretical progress, practical quantum coin-flipping protocols with vanishing bias have proved hard to find. In the current work we show that there is a reason that practical weak quantum coin-flipping is difficult: any quantum weak coin-flipping protocol with bias є must use at least exp( Ω (1/√є )) rounds of communication. This is a large improvement over the previous best known lower bound of Ω ( log log(1/є )) due to Ambainis from 2004. Our proof is based on a theoretical construction (the two-variable profile function) which may find further applications.

1 aMiller, Carl uhttps://www.quics.umd.edu/publications/impossibility-efficient-quantum-weak-coin-flipping-001522nas a2200193 4500008004100000245005900041210005700100260001400157490000800171520097200179100002301151700001801174700001801192700001601210700002301226700001801249700002401267856003701291 2020 eng d00aMany-Body Dephasing in a Trapped-Ion Quantum Simulator0 aManyBody Dephasing in a TrappedIon Quantum Simulator c8/24/20200 v1253 a

How a closed interacting quantum many-body system relaxes and dephases as a function of time is a fundamental question in thermodynamic and statistical physics. In this work, we observe and analyse the persistent temporal fluctuations after a quantum quench of a tunable long-range interacting transverse-field Ising Hamiltonian realized with a trapped-ion quantum simulator. We measure the temporal fluctuations in the average magnetization of a finite-size system of spin-1/2 particles and observe the experimental evidence for the theoretically predicted regime of many-body dephasing. We experiment in a regime where the properties of the system are closely related to the integrable Hamiltonian with global spin-spin coupling, which enables analytical predictions even for the long-time non-integrable dynamics. We find that the measured fluctuations are exponentially suppressed with increasing system size, consistent with theoretical predictions. 

1 aKaplan, Harvey, B.1 aGuo, Lingzhen1 aTan, Wen, Lin1 aDe, Arinjoy1 aMarquardt, Florian1 aPagano, Guido1 aMonroe, Christopher uhttps://arxiv.org/abs/2001.0247702026nas a2200517 4500008004100000245006100041210006100102260001400163520075200177100001500929700001600944700001800960700001800978700001300996700001401009700001701023700001601040700001401056700001701070700001501087700001401102700002201116700001301138700001701151700001801168700001701186700001101203700001201214700001201226700001501238700001601253700001501269700001801284700001401302700001701316700001401333700001901347700001401366700001401380700001401394700001901408700001201427700001901439700001301458856003701471 2020 eng d00aMechanical Quantum Sensing in the Search for Dark Matter0 aMechanical Quantum Sensing in the Search for Dark Matter c8/13/20203 a

Numerous astrophysical and cosmological observations are best explained by the existence of dark matter, a mass density which interacts only very weakly with visible, baryonic matter. Searching for the extremely weak signals produced by this dark matter strongly motivate the development of new, ultra-sensitive detector technologies. Paradigmatic advances in the control and readout of massive mechanical systems, in both the classical and quantum regimes, have enabled unprecedented levels of sensitivity. In this white paper, we outline recent ideas in the potential use of a range of solid-state mechanical sensing technologies to aid in the search for dark matter in a number of energy scales and with a variety of coupling mechanisms.

1 aCarney, D.1 aKrnjaic, G.1 aMoore, D., C.1 aRegal, C., A.1 aAfek, G.1 aBhave, S.1 aBrubaker, B.1 aCorbitt, T.1 aCripe, J.1 aCrisosto, N.1 a.Geraci, A1 aGhosh, S.1 aHarris, J., G. E.1 aHook, A.1 aKolb, E., W.1 aKunjummen, J.1 aLang, R., F.1 aLi, T.1 aLin, T.1 aLiu, Z.1 aLykken, J.1 aMagrini, L.1 aManley, J.1 aMatsumoto, N.1 aMonte, A.1 aMonteiro, F.1 aPurdy, T.1 aRiedel, C., J.1 aSingh, R.1 aSingh, S.1 aSinha, K.1 aTaylor, J., M.1 aQin, J.1 aWilson, D., J.1 aZhao, Y. uhttps://arxiv.org/abs/2008.0607402329nas a2200157 4500008004100000245005700041210005600098260001400154490000700168520186200175100002202037700002502059700002302084700002702107856003702134 2020 eng d00aNon-equilibrium fixed points of coupled Ising models0 aNonequilibrium fixed points of coupled Ising models c2/26/20200 v103 a

Driven-dissipative systems can exhibit non-equilibrium phenomena that are absent in their equilibrium counterparts. However, phase transitions present in these systems generically exhibit an effectively classical equilibrium behavior in spite of their quantum non-equilibrium origin. In this paper, we show that multicritical points in driven-dissipative systems can give rise to genuinely non-equilibrium behavior. We investigate a non-equilibrium driven-dissipative model of interacting bosons that exhibits two distinct phase transitions: one from a high- to a low-density phase---reminiscent of a liquid-gas transition---and another to an antiferromagnetic phase. Each phase transition is described by the Ising universality class characterized by an (emergent or microscopic) Z2 symmetry. They, however, coalesce at a multicritical point giving rise to a non-equilibrium model of coupled Ising-like order parameters described by a Z2×Z2 symmetry. Using a dynamical renormalization-group approach, we show that a pair of non-equilibrium fixed points (NEFPs) emerge that govern the long-distance critical behavior of the system. We elucidate various exotic features of these NEFPs. In particular, we show that a generic continuous scale invariance at criticality is reduced to a discrete scale invariance. This further results in complex-valued critical exponents, spiraling phase boundaries, and a complex Liouvillian gap even close to the phase transition. As direct evidence of the non-equilibrium nature of the NEFPs, we show that the fluctuation-dissipation relation is violated at all scales, leading to an effective temperature that becomes "hotter" and "hotter" at longer and longer wavelengths. Finally, we argue that this non-equilibrium behavior can be observed in cavity arrays with cross-Kerr nonlinearities.

1 aYoung, Jeremy, T.1 aGorshkov, Alexey, V.1 aFoss-Feig, Michael1 aMaghrebi, Mohammad, F. uhttps://arxiv.org/abs/1903.0256901795nas a2200157 4500008004100000245008800041210006900129260001400198520128700212100002501499700001701524700002201541700001901563700001801582856003701600 2020 eng d00aA note on blind contact tracing at scale with applications to the COVID-19 pandemic0 anote on blind contact tracing at scale with applications to the  c4/10/20203 a

The current COVID-19 pandemic highlights the utility of contact tracing, when combined with case isolation and social distancing, as an important tool for mitigating the spread of a disease [1]. Contact tracing provides a mechanism of identifying individuals with a high likelihood of previous exposure to a contagious disease, allowing additional precautions to be put in place to prevent continued transmission. Here we consider a cryptographic approach to contact tracing based on secure two-party computation (2PC). We begin by considering the problem of comparing a set of location histories held by two parties to determine whether they have come within some threshold distance while at the same time maintaining the privacy of the location histories. We propose a solution to this problem using pre-shared keys, adapted from an equality testing protocol due to Ishai et al [2]. We discuss how this protocol can be used to maintain privacy within practical contact tracing scenarios, including both app-based approaches and approaches which leverage location history held by telecoms and internet service providers. We examine the efficiency of this approach and show that existing infrastructure is sufficient to support anonymised contact tracing at a national level.

1 aFitzsimons, Jack, K.1 aMantri, Atul1 aPisarczyk, Robert1 aRainforth, Tom1 aZhao, Zhikuan uhttps://arxiv.org/abs/2004.0511601576nas a2200157 4500008004100000245010800041210006900149260001400218490000600232520106400238100001701302700001601319700002701335700001901362856003701381 2020 eng d00aOptimal fermion-to-qubit mapping via ternary trees with applications to reduced quantum states learning0 aOptimal fermiontoqubit mapping via ternary trees with applicatio c5/26/20200 v43 a

We introduce a fermion-to-qubit mapping defined on ternary trees, where any single Majorana operator on an n-mode fermionic system is mapped to a multi-qubit Pauli operator acting nontrivially on ⌈log3(2n+1)⌉ qubits. The mapping has a simple structure and is optimal in the sense that it is impossible to construct Pauli operators in any fermion-to-qubit mapping acting nontrivially on less than log3(2n) qubits on average. We apply it to the problem of learning k-fermion reduced density matrix (RDM), a problem relevant in various quantum simulation applications. We show that using the ternary-tree mapping one can determine the elements of all k-fermion RDMs, to precision ϵ, by repeating a single quantum circuit for ≲(2n+1)kϵ−2 times. This result is based on a method we develop here that allows one to determine the elements of all k-qubit RDMs, to precision ϵ, by repeating a single quantum circuit for ≲3kϵ−2 times, independent of the system size. This improves over existing schemes for determining qubit RDMs.

1 aJiang, Zhang1 aKalev, Amir1 aMruczkiewicz, Wojciech1 aNeven, Hartmut uhttps://arxiv.org/abs/1910.1074601468nas a2200157 4500008004100000245005700041210005600098260001200154300001400166490000700180520103700187100001601224700001701240700001601257856003701273 2020 eng d00aParallel Device-Independent Quantum Key Distribution0 aParallel DeviceIndependent Quantum Key Distribution c09/2020 a5567-55840 v663 a

A prominent application of quantum cryptography is the distribution of cryptographic keys that are provably secure. Such security proofs were extended by Vazirani and Vidick ( Physical Review Letters , 113, 140501, 2014) to the device-independent (DI) scenario, where the users do not need to trust the integrity of the underlying quantum devices. The protocols analyzed by them and by subsequent authors all require a sequential execution of N multiplayer games, where N is the security parameter. In this work, we prove the security of a protocol where all games are executed in parallel. Besides decreasing the number of time-steps necessary for key generation, this result reduces the security requirements for DI-QKD by allowing arbitrary information leakage of each user’s inputs within his or her lab. To the best of our knowledge, this is the first parallel security proof for a fully device-independent QKD protocol. Our protocol tolerates a constant level of device imprecision and achieves a linear key rate.

1 aJain, Rahul1 aMiller, Carl1 aShi, Yaoyun uhttps://arxiv.org/abs/1703.0542601620nas a2200193 4500008004100000245006300041210006200104260001400166520106800180100001201248700001401260700001901274700002101293700002101314700001801335700001501353700002101368856003701389 2020 eng d00aProbing many-body localization on a noisy quantum computer0 aProbing manybody localization on a noisy quantum computer c6/22/20203 a

A disordered system of interacting particles exhibits localized behavior when the disorder is large compared to the interaction strength. Studying this phenomenon on a quantum computer without error correction is challenging because even weak coupling to a thermal environment destroys most signatures of localization. Fortunately, spectral functions of local operators are known to contain features that can survive the presence of noise. In these spectra, discrete peaks and a soft gap at low frequencies compared to the thermal phase indicate localization. Here, we present the computation of spectral functions on a trapped-ion quantum computer for a one-dimensional Heisenberg model with disorder. Further, we design an error-mitigation technique which is effective at removing the noise from the measurement allowing clear signatures of localization to emerge as the disorder increases. Thus, we show that spectral functions can serve as a robust and scalable diagnostic of many-body localization on the current generation of quantum computers. 

1 aZhu, D.1 aJohri, S.1 aNguyen, N., H.1 aAlderete, Huerta1 aLandsman, K., A.1 aLinke, N., M.1 aMonroe, C.1 aMatsuura, A., Y. uhttps://arxiv.org/abs/2006.1235501551nas a2200193 4500008004100000245009300041210006900134260001300203520092900216100002101145700001901166700002201185700001601207700002401223700002401247700002601271700002301297856003701320 2020 eng d00aQuantum walks and Dirac cellular automata on a programmable trapped-ion quantum computer0 aQuantum walks and Dirac cellular automata on a programmable trap c2/6/20203 a

The quantum walk formalism is a widely used and highly successful framework for modeling quantum systems, such as simulations of the Dirac equation, different dynamics in both the low and high energy regime, and for developing a wide range of quantum algorithms. Here we present the circuit-based implementation of a discrete-time quantum walk in position space on a five-qubit trapped-ion quantum processor. We encode the space of walker positions in particular multi-qubit states and program the system to operate with different quantum walk parameters, experimentally realizing a Dirac cellular automaton with tunable mass parameter. The quantum walk circuits and position state mapping scale favorably to a larger model and physical systems, allowing the implementation of any algorithm based on discrete-time quantum walks algorithm and the dynamics associated with the discretized version of the Dirac equation.

1 aAlderete, Huerta1 aSingh, Shivani1 aNguyen, Nhung, H.1 aZhu, Daiwei1 aBalu, Radhakrishnan1 aMonroe, Christopher1 aChandrashekar, C., M.1 aLinke, Norbert, M. uhttps://arxiv.org/abs/2002.0253702359nas a2200169 4500008004100000245007400041210006900115260001300184300001300197490001000210520178100220100001902001700002202020700002302042700001502065856010902080 2020 eng d00aQuantum-Access-Secure Message Authentication via Blind-Unforgeability0 aQuantumAccessSecure Message Authentication via BlindUnforgeabili c5/1/2020 a788-817 0 v12-173 a

Formulating and designing authentication of classical messages in the presence of adversaries with quantum query access has been a longstanding challenge, as the familiar classical notions of unforgeability do not directly translate into meaningful notions in the quantum setting. A particular difficulty is how to fairly capture the notion of “predicting an unqueried value” when the adversary can query in quantum superposition.

We propose a natural definition of unforgeability against quantum adversaries called blind unforgeability. This notion defines a function to be predictable if there exists an adversary who can use “partially blinded” oracle access to predict values in the blinded region. We support the proposal with a number of technical results. We begin by establishing that the notion coincides with EUF-CMA in the classical setting and go on to demonstrate that the notion is satisfied by a number of simple guiding examples, such as random functions and quantum-query-secure pseudorandom functions. We then show the suitability of blind unforgeability for supporting canonical constructions and reductions. We prove that the “hash-and-MAC” paradigm and the Lamport one-time digital signature scheme are indeed unforgeable according to the definition. To support our analysis, we additionally define and study a new variety of quantum-secure hash functions called Bernoulli-preserving.

Finally, we demonstrate that blind unforgeability is strictly stronger than a previous definition of Boneh and Zhandry [EUROCRYPT ’13, CRYPTO ’13] and resolve an open problem concerning this previous definition by constructing an explicit function family which is forgeable yet satisfies the definition.

1 aAlagic, Gorjan1 aMajenz, Christian1 aRussell, Alexander1 aSong, Fang uhttps://www.quics.umd.edu/publications/quantum-access-secure-message-authentication-blind-unforgeability01423nas a2200157 4500008004100000245006500041210006300106260001400169520093400183100002401117700002601141700002101167700002101188700001901209856003701228 2020 eng d00aRay-based classification framework for high-dimensional data0 aRaybased classification framework for highdimensional data c10/1/20203 a

While classification of arbitrary structures in high dimensions may require complete quantitative information, for simple geometrical structures, low-dimensional qualitative information about the boundaries defining the structures can suffice. Rather than using dense, multi-dimensional data, we propose a deep neural network (DNN) classification framework that utilizes a minimal collection of one-dimensional representations, called \emph{rays}, to construct the "fingerprint" of the structure(s) based on substantially reduced information. We empirically study this framework using a synthetic dataset of double and triple quantum dot devices and apply it to the classification problem of identifying the device state. We show that the performance of the ray-based classifier is already on par with traditional 2D images for low dimensional systems, while significantly cutting down the data acquisition cost.

1 aZwolak, Justyna, P.1 aKalantre, Sandesh, S.1 aMcJunkin, Thomas1 aWeber, Brian, J.1 aTaylor, J., M. uhttps://arxiv.org/abs/2010.0050001697nas a2200181 4500008004100000245007000041210006900111260001400180490000800194520115900202100002301361700001501384700001901399700002001418700001901438700002101457856003701478 2020 eng d00aSearch for composite dark matter with optically levitated sensors0 aSearch for composite dark matter with optically levitated sensor c11/2/20200 v1253 a

Results are reported from a search for a class of composite dark matter models with feeble, long-range interactions with normal matter. We search for impulses arising from passing dark matter particles by monitoring the mechanical motion of an optically levitated nanogram mass over the course of several days. Assuming such particles constitute the dominant component of dark matter, this search places upper limits on their interaction with neutrons of αn≤1.2×10−7 at 95\% confidence for dark matter masses between 1--10 TeV and mediator masses mφ≤0.1 eV. Due to the large enhancement of the cross-section for dark matter to coherently scatter from a nanogram mass (∼1029 times that for a single neutron) and the ability to detect momentum transfers as small as ∼200 MeV/c, these results provide sensitivity to certain classes of composite dark matter models that substantially exceeds existing searches, including those employing kg-scale or ton-scale targets. Extensions of these techniques can enable directionally-sensitive searches for a broad class of previously inaccessible heavy dark matter candidates. 

1 aMonteiro, Fernando1 aAfek, Gadi1 aCarney, Daniel1 aKrnjaic, Gordan1 aWang, Jiaxiang1 aMoore, David, C. uhttps://arxiv.org/abs/2007.1206702382nas a2200145 4500008004100000245007400041210006900115260001500184520192100199100001902120700002402139700001902163700001702182856003702199 2020 eng d00aSecure Quantum Two-Party Computation: Impossibility and Constructions0 aSecure Quantum TwoParty Computation Impossibility and Constructi c10/15/20203 a

Secure two-party computation considers the problem of two parties computing a joint function of their private inputs without revealing anything beyond the output of the computation. In this work, we take the first steps towards understanding the setting in which the two parties want to evaluate a joint quantum functionality while using only a classical channel between them. Our first result indicates that it is in general impossible to realize a two-party quantum functionality against malicious adversaries with black-box simulation, relying only on classical channels. The negative result stems from reducing the existence of a black-box simulator to an extractor for classical proof of quantum knowledge, which in turn leads to violation of the quantum no-cloning. Next, we introduce the notion of oblivious quantum function evaluation (OQFE). An OQFE is a two-party quantum cryptographic primitive with one fully classical party (Alice) whose input is (a classical description of a) quantum unitary, U, and a quantum party (Bob) whose input is a quantum state, ψ. In particular, Alice receives a classical output corresponding to the measurement of U(ψ) while Bob receives no output. In OQFE, Bob remains oblivious to Alice's input, while Alice learns nothing about ψ more than what can be learned from the output. We present two constructions, one secure against semi-honest parties and the other against malicious parties. Due to the no-go result mentioned above, we consider what is arguably the best possible notion obtainable in our model concerning malicious adversaries: one-sided simulation security. Our protocol relies on the assumption of injective homomorphic trapdoor OWFs, which in turn rely on the LWE problem. As a result, we put forward a first, simple and modular, construction of one-sided quantum two-party computation and quantum oblivious transfer over classical networks.

1 aCiamp, Michele1 aCojocaru, Alexandru1 aKashefi, Elham1 aMantri, Atul uhttps://arxiv.org/abs/2010.0792502441nas a2200181 4500008004100000245007300041210006900114260001300183520187800196100002702074700002402101700001902125700001902144700002202163700001702185700002002202856003702222 2020 eng d00aSecurity Limitations of Classical-Client Delegated Quantum Computing0 aSecurity Limitations of ClassicalClient Delegated Quantum Comput c7/3/20203 a

Secure delegated quantum computing allows a computationally weak client to outsource an arbitrary quantum computation to an untrusted quantum server in a privacy-preserving manner. One of the promising candidates to achieve classical delegation of quantum computation is classical-client remote state preparation (RSPCC), where a client remotely prepares a quantum state using a classical channel. However, the privacy loss incurred by employing RSPCC as a sub-module is unclear.
In this work, we investigate this question using the Constructive Cryptography framework by Maurer and Renner (ICS'11). We first identify the goal of RSPCC as the construction of ideal RSP resources from classical channels and then reveal the security limitations of using RSPCC. First, we uncover a fundamental relationship between constructing ideal RSP resources (from classical channels) and the task of cloning quantum states. Any classically constructed ideal RSP resource must leak to the server the full classical description (possibly in an encoded form) of the generated quantum state, even if we target computational security only. As a consequence, we find that the realization of common RSP resources, without weakening their guarantees drastically, is impossible due to the no-cloning theorem. Second, the above result does not rule out that a specific RSPCC protocol can replace the quantum channel at least in some contexts, such as the Universal Blind Quantum Computing (UBQC) protocol of Broadbent et al. (FOCS '09). However, we show that the resulting UBQC protocol cannot maintain its proven composable security as soon as RSPCC is used as a subroutine. Third, we show that replacing the quantum channel of the above UBQC protocol by the RSPCC protocol QFactory of Cojocaru et al. (Asiacrypt '19), preserves the weaker, game-based, security of UBQC.

1 aBadertscher, Christian1 aCojocaru, Alexandru1 aColisson, Léo1 aKashefi, Elham1 aLeichtle, Dominik1 aMantri, Atul1 aWallden, Petros uhttps://arxiv.org/abs/2007.0166803210nas a2200253 4500008004100000245010000041210006900141260001200210520236500222100001902587700002702606700001702633700001802650700001602668700001702684700001602701700001702717700001802734700001802752700001702770700002102787700002302808856012502831 2020 eng d00aStatus Report on the Second Round of the NIST Post-Quantum Cryptography Standardization Process0 aStatus Report on the Second Round of the NIST PostQuantum Crypto c07/20203 a

The National Institute of Standards and Technology is in the process of selecting one or more public-key cryptographic algorithms through a public, competition-like process. The new public-key cryptography standards will specify one or more additional digital signatures, public-key encryption, and key-establishment algorithms to augment Federal Information Processing Standard (FIPS) 186-4, Digital Signature Standard (DSS), as well as NIST Special Publication (SP) 800-56A Revision 3, Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography, and SP 800-56B Revision 2, Recommendation for Pair-Wise Key Establishment Using Integer Factorization Cryptography. It is intended that these algorithms will be capable of protecting sensitive information well into the foreseeable future, including after the advent of quantum computers.

The NIST Post-Quantum Cryptography Standardization Process began in 2017 with 69 candidate algorithms that met both the minimum acceptance criteria and submission requirements. The first round lasted until January 2019, during which candidate algorithms were evaluated based on their security, performance, and other characteristics. NIST selected 26 algorithms to advance to the second round for more analysis. This report describes the evaluation and selection process, based on public feedback and internal review, of the second-round candidates. The report summarizes the 26 second-round candidate algorithms and identifies those selected to move forward to the third round of the competition. The third-round finalist public-key encryption and key-establishment algorithms are Classic McEliece, CRYSTALS-KYBER, NTRU, and SABER. The third-round finalists for digital signatures are CRYSTALS-DILITHIUM, FALCON, and Rainbow. These finalists will be considered for standardization at the end of the third round. In addition, eight alternate candidate algorithms will also advance to the third round: BIKE, FrodoKEM, HQC, NTRU Prime, SIKE, GeMSS, Picnic, and SPHINCS+. These additional candidates are still being considered for standardization, although this is unlikely to occur at the end of the third round. NIST hopes that the announcement of these finalists and additional candidates will serve to focus the cryptographic community’s attention during the next round.

1 aAlagic, Gorjan1 aAlperin-Sheriff, Jacob1 aApon, Daniel1 aCooper, David1 aDang, Quynh1 aKelsey, John1 aLiu, Yi-Kai1 aMiller, Carl1 aMoody, Dustin1 aPeralta, Rene1 aPerlner, Ray1 aRobinson, Angela1 aSmith-Tone, Daniel uhttps://www.quics.umd.edu/publications/status-report-second-round-nist-post-quantum-cryptography-standardization-process01870nas a2200181 4500008004100000245008300041210006900124260001300193490000600206520132100212100002001533700002101553700002401574700001801598700001801616700001701634856003701651 2020 eng d00aTowards analog quantum simulations of lattice gauge theories with trapped ions0 aTowards analog quantum simulations of lattice gauge theories wit c4/8/20200 v23 a

Gauge field theories play a central role in modern physics and are at the heart of the Standard Model of elementary particles and interactions. Despite significant progress in applying classical computational techniques to simulate gauge theories, it has remained a challenging task to compute the real-time dynamics of systems described by gauge theories. An exciting possibility that has been explored in recent years is the use of highly-controlled quantum systems to simulate, in an analog fashion, properties of a target system whose dynamics are difficult to compute. Engineered atom-laser interactions in a linear crystal of trapped ions offer a wide range of possibilities for quantum simulations of complex physical systems. Here, we devise practical proposals for analog simulation of simple lattice gauge theories whose dynamics can be mapped onto spin-spin interactions in any dimension. These include 1+1D quantum electrodynamics, 2+1D Abelian Chern-Simons theory coupled to fermions, and 2+1D pure Z2 gauge theory. The scheme proposed, along with the optimization protocol applied, will have applications beyond the examples presented in this work, and will enable scalable analog quantum simulation of Heisenberg spin models in any number of dimensions and with arbitrary interaction strengths.

1 aDavoudi, Zohreh1 aHafezi, Mohammad1 aMonroe, Christopher1 aPagano, Guido1 aSeif, Alireza1 aShaw, Andrew uhttps://arxiv.org/abs/1908.0321001282nas a2200133 4500008004100000245006000041210006000101260001500161490000800176520088800184100001801072700002101090856003701111 2020 eng d00aUnitary Subharmonic Response and Floquet Majorana Modes0 aUnitary Subharmonic Response and Floquet Majorana Modes c10/13/20200 v1253 a

Detection and manipulation of excitations with non-Abelian statistics, such as Majorana fermions, are essential for creating topological quantum computers. To this end, we show the connection between the existence of such localized particles and the phenomenon of unitary subharmonic response (SR) in periodically driven systems. In particular, starting from highly non-equilibrium initial states, the unpaired Majorana modes exhibit spin oscillations with twice the driving period, are localized, and can have exponentially long lifetimes in clean systems. While the lifetime of SR is limited in translationally invariant systems, we show that disorder can be engineered to stabilize the subharmonic response of Majorana modes. A viable observation of this phenomenon can be achieved using modern multi-qubit hardware, such as superconducting circuits and cold atomic systems

1 aShtanko, Oles1 aMovassagh, Ramis uhttps://arxiv.org/abs/1911.0579501306nas a2200169 4500008004100000245011300041210006900154260001400223520072000237100001900957700002600976700002401002700002401026700002301050700002601073856003701099 2020 eng d00aUniversal one-dimensional discrete-time quantum walks and their implementation on near term quantum hardware0 aUniversal onedimensional discretetime quantum walks and their im c1/30/20203 a

Quantum walks are a promising framework for developing quantum algorithms and quantum simulations. Quantum walks represent an important test case for the application of quantum computers. Here we present different forms of discrete-time quantum walks and show their equivalence for physical realizations. Using an appropriate digital mapping of the position space on which a walker evolves onto the multi-qubit states in a quantum processor, we present different configurations of quantum circuits for the implementation of discrete-time quantum walks in one-dimensional position space. With example circuits for a five qubit machine we address scalability to higher dimensions and larger quantum processors.

1 aSingh, Shivani1 aAlderete, Cinthia, H.1 aBalu, Radhakrishnan1 aMonroe, Christopher1 aLinke, Norbert, M.1 aChandrashekar, C., M. uhttps://arxiv.org/abs/2001.1119701524nas a2200145 4500008004100000245004700041210004400088260001500132520110100147100003701248700001801285700001901303700001901322856003701341 2019 eng d00aCompeting (Semi)-Selfish Miners in Bitcoin0 aCompeting SemiSelfish Miners in Bitcoin c06/11/20193 a

The Bitcoin protocol prescribes certain behavior by the miners who are responsible for maintaining and extending the underlying blockchain; in particular, miners who successfully solve a puzzle, and hence can extend the chain by a block, are supposed to release that block immediately. Eyal and Sirer showed, however, that a selfish miner is incentivized to deviate from the protocol and withhold its blocks under certain conditions. The analysis by Eyal and Sirer, as well as in followup work, considers a \emph{single} deviating miner (who may control a large fraction of the hashing power in the network) interacting with a remaining pool of honest miners. Here, we extend this analysis to the case where there are \emph{multiple} (non-colluding) selfish miners. We find that with multiple strategic miners, specific deviations from honest mining by multiple strategic agents can outperform honest mining, even if individually miners would not be incentivised to be dishonest. This previous point effectively renders the Bitcoin protocol to be less secure than previously thought. 

1 aMarmolejo-Cossío, Francisco, J.1 aBrigham, Eric1 aSela, Benjamin1 aKatz, Jonathan uhttps://arxiv.org/abs/1906.0450201697nas a2200169 4500008004100000245008100041210006900122260001500191520115700206100002001363700002301383700001901406700002001425700002001445700002501465856003701490 2019 eng d00aComplexity phase diagram for interacting and long-range bosonic Hamiltonians0 aComplexity phase diagram for interacting and longrange bosonic H c06/10/20193 a

Recent years have witnessed a growing interest in topics at the intersection of many-body physics and complexity theory. Many-body physics aims to understand and classify emergent behavior of systems with a large number of particles, while complexity theory aims to classify computational problems based on how the time required to solve the problem scales as the problem size becomes large. In this work, we use insights from complexity theory to classify phases in interacting many-body systems. Specifically, we demonstrate a "complexity phase diagram" for the Bose-Hubbard model with long-range hopping. This shows how the complexity of simulating time evolution varies according to various parameters appearing in the problem, such as the evolution time, the particle density, and the degree of locality. We find that classification of complexity phases is closely related to upper bounds on the spread of quantum correlations, and protocols to transfer quantum information in a controlled manner. Our work motivates future studies of complexity in many-body systems and its interplay with the associated physical phenomena. 

1 aMaskara, Nishad1 aDeshpande, Abhinav1 aTran, Minh, C.1 aEhrenberg, Adam1 aFefferman, Bill1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1906.0417801746nas a2200193 4500008004100000245006800041210006700109260001500176490000900191520117800200100001601378700001801394700001701412700001801429700001901447700002401466700002501490856003701515 2019 eng d00aConfined Dynamics in Long-Range Interacting Quantum Spin Chains0 aConfined Dynamics in LongRange Interacting Quantum Spin Chains c04/17/20190 v122 3 a

We study the quasiparticle excitation and quench dynamics of the one-dimensional transverse-field Ising model with power-law (1/rα) interactions. We find that long-range interactions give rise to a confining potential, which couples pairs of domain walls (kinks) into bound quasiparticles, analogous to mesonic bound states in high-energy physics. We show that these bound states have dramatic consequences for the non-equilibrium dynamics following a global quantum quench, such as suppressed spreading of quantum information and oscillations of order parameters. The masses of these bound states can be read out from the Fourier spectrum of these oscillating order parameters. We then use a two-kink model to qualitatively explain the phenomenon of long-range-interaction-induced confinement. The masses of the bound states predicted by this model are in good quantitative agreement with exact diagonalization results. Moreover, we illustrate that these bound states lead to weak thermalization of local observables for initial states with energy near the bottom of the many-body energy spectrum. Our work is readily applicable to current trapped-ion experiments.

1 aLiu, Fangli1 aLundgren, Rex1 aTitum, Paraj1 aPagano, Guido1 aZhang, Jiehang1 aMonroe, Christopher1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1810.0236502955nas a2200397 4500008004100000245008600041210006900127260001500196520181200211100002102023700002302044700002002067700001702087700002202104700001702126700002502143700001802168700001902186700001702205700001702222700002702239700001502266700001702281700001802298700001702316700001602333700002002349700001902369700002302388700002502411700002402436700001802460700002002478700002202498856003702520 2019 eng d00aDevelopment of Quantum InterConnects for Next-Generation Information Technologies0 aDevelopment of Quantum InterConnects for NextGeneration Informat c12/13/20193 a

Just as classical information technology rests on a foundation built of interconnected information-processing systems, quantum information technology (QIT) must do the same. A critical component of such systems is the interconnect, a device or process that allows transfer of information between disparate physical media, for example, semiconductor electronics, individual atoms, light pulses in optical fiber, or microwave fields. While interconnects have been well engineered for decades in the realm of classical information technology, quantum interconnects (QuICs) present special challenges, as they must allow the transfer of fragile quantum states between different physical parts or degrees of freedom of the system. The diversity of QIT platforms (superconducting, atomic, solid-state color center, optical, etc.) that will form a quantum internet poses additional challenges. As quantum systems scale to larger size, the quantum interconnect bottleneck is imminent, and is emerging as a grand challenge for QIT. For these reasons, it is the position of the community represented by participants of the NSF workshop on Quantum Interconnects that accelerating QuIC research is crucial for sustained development of a national quantum science and technology program. Given the diversity of QIT platforms, materials used, applications, and infrastructure required, a convergent research program including partnership between academia, industry and national laboratories is required. This document is a summary from a U.S. National Science Foundation supported workshop held on 31 October - 1 November 2019 in Alexandria, VA. Attendees were charged to identify the scientific and community needs, opportunities, and significant challenges for quantum interconnects over the next 2-5 years. 

1 aAwschalom, David1 aBerggren, Karl, K.1 aBernien, Hannes1 aBhave, Sunil1 aCarr, Lincoln, D.1 aDavids, Paul1 aEconomou, Sophia, E.1 aEnglund, Dirk1 aFaraon, Andrei1 aFejer, Marty1 aGuha, Saikat1 aGustafsson, Martin, V.1 aHu, Evelyn1 aJiang, Liang1 aKim, Jungsang1 aKorzh, Boris1 aKumar, Prem1 aKwiat, Paul, G.1 aLončar, Marko1 aLukin, Mikhail, D.1 aMiller, David, A. B.1 aMonroe, Christopher1 aNam, Sae, Woo1 aNarang, Prineha1 aOrcutt, Jason, S. uhttps://arxiv.org/abs/1912.0664201739nas a2200205 4500008004100000245013400041210006900175260001500244520106400259100001801323700001201341700002201353700001701375700002501392700001301417700001901430700002601449700002101475856003701496 2019 eng d00aFeshbach resonances in p-wave three-body recombination within Fermi-Fermi mixtures of open-shell 6Li and closed-shell 173Yb atoms0 aFeshbach resonances in pwave threebody recombination within Ferm c12/10/20193 a

We report on observations and modeling of interspecies magnetic Feshbach resonances in dilute ultracold mixtures of open-shell alkali-metal 6Li and closed-shell 173Yb atoms with temperatures just above quantum degeneracy for both fermionic species. Resonances are located by detecting magnetic-field-dependent atom loss due to three-body recombination. We resolve closely-located resonances that originate from a weak separation-dependent hyperfine coupling between the electronic spin of 6Li and the nuclear spin of 173Yb, and confirm their magnetic field spacing by ab initio electronic-structure calculations. Through quantitative comparisons of theoretical atom-loss profiles and experimental data at various temperatures between 1 μK and 20 μK, we show that three-body recombination in fermionic mixtures has a p-wave Wigner threshold behavior leading to characteristic asymmetric loss profiles. Such resonances can be applied towards the formation of ultracold doublet ground-state molecules and quantum simulation of superfluid p-wave pairing.

1 aGreen, Alaina1 aLi, Hui1 aToh, Jun, Hui See1 aTang, Xinxin1 aMcCormick, Katherine1 aLi, Ming1 aTiesinga, Eite1 aKotochigova, Svetlana1 aGupta, Subhadeep uhttps://arxiv.org/abs/1912.0487401300nas a2200145 4500008004100000245008500041210006900126260001300195490000800208520083900216100002101055700002501076700001601101856003701117 2019 eng d00aFluctuation-induced torque on a topological insulator out of thermal equilibrium0 aFluctuationinduced torque on a topological insulator out of ther c8/1/20190 v1233 a

Topological insulators with the time reversal symmetry broken exhibit strong magnetoelectric and magneto-optic effects. While these effects are well-understood in or near equilibrium, nonequilibrium physics is richer yet less explored. We consider a topological insulator thin film, weakly coupled to a ferromagnet, out of thermal equilibrium with a cold environment (quantum electrodynamics vacuum). We show that the heat flow to the environment is strongly circularly polarized, thus carrying away angular momentum and exerting a purely fluctuation-driven torque on the topological insulator film. Utilizing the Keldysh framework, we investigate the universal nonequilibrium response of the TI to the temperature difference with the environment. Finally, we argue that experimental observation of this effect is within reach.

1 aMaghrebi, M., F.1 aGorshkov, Alexey, V.1 aSau, J., D. uhttps://arxiv.org/abs/1811.0608001242nas a2200145 4500008004100000245006500041210006400106260001500170490000600185520081100191100002101002700001701023700001901040856003701059 2019 eng d00aGraphical Methods in Device-Independent Quantum Cryptography0 aGraphical Methods in DeviceIndependent Quantum Cryptography c05/20/20190 v33 a

We introduce a framework for graphical security proofs in device-independent quantum cryptography using the methods of categorical quantum mechanics. We are optimistic that this approach will make some of the highly complex proofs in quantum cryptography more accessible, facilitate the discovery of new proofs, and enable automated proof verification. As an example of our framework, we reprove a recent result from device-independent quantum cryptography: any linear randomness expansion protocol can be converted into an unbounded randomness expansion protocol. We give a graphical exposition of a proof of this result and implement parts of it in the Globular proof assistant.

1 aBreiner, Spencer1 aMiller, Carl1 aRoss, Neil, J. uhttps://arxiv.org/abs/1705.0921302376nas a2200409 4500008004100000245009100041210006900132260001500201520116700216100001801383700001701401700002201418700002001440700001901460700001901479700002301498700001901521700002101540700001901561700002201580700002001602700002201622700002201644700002101666700002201687700002301709700001901732700002001751700002701771700002201798700001801820700001901838700003001857700002401887700001801911856003701929 2019 eng d00aGround-state energy estimation of the water molecule on a trapped ion quantum computer0 aGroundstate energy estimation of the water molecule on a trapped c03/07/20193 a

Quantum computing leverages the quantum resources of superposition and entanglement to efficiently solve computational problems considered intractable for classical computers. Examples include calculating molecular and nuclear structure, simulating strongly-interacting electron systems, and modeling aspects of material function. While substantial theoretical advances have been made in mapping these problems to quantum algorithms, there remains a large gap between the resource requirements for solving such problems and the capabilities of currently available quantum hardware. Bridging this gap will require a co-design approach, where the expression of algorithms is developed in conjunction with the hardware itself to optimize execution. Here, we describe a scalable co-design framework for solving chemistry problems on a trapped ion quantum computer, and apply it to compute the ground-state energy of the water molecule. The robust operation of the trapped ion quantum computer yields energy estimates with errors approaching the chemical accuracy, which is the target threshold necessary for predicting the rates of chemical reaction dynamics.

1 aNam, Yunseong1 aChen, Jwo-Sy1 aPisenti, Neal, C.1 aWright, Kenneth1 aDelaney, Conor1 aMaslov, Dmitri1 aBrown, Kenneth, R.1 aAllen, Stewart1 aAmini, Jason, M.1 aApisdorf, Joel1 aBeck, Kristin, M.1 aBlinov, Aleksey1 aChaplin, Vandiver1 aChmielewski, Mika1 aCollins, Coleman1 aDebnath, Shantanu1 aDucore, Andrew, M.1 aHudek, Kai, M.1 aKeesan, Matthew1 aKreikemeier, Sarah, M.1 aMizrahi, Jonathan1 aSolomon, Phil1 aWilliams, Mike1 aWong-Campos, Jaime, David1 aMonroe, Christopher1 aKim, Jungsang uhttps://arxiv.org/abs/1902.1017101196nas a2200193 4500008004100000245009600041210006900137260001400206490000800220520059500228100001600823700002200839700001600861700001800877700002400895700002100919700002500940856003700965 2019 eng d00aHeisenberg-Scaling Measurement Protocol for Analytic Functions with Quantum Sensor Networks0 aHeisenbergScaling Measurement Protocol for Analytic Functions wi c10/7/20190 v1003 a

We generalize past work on quantum sensor networks to show that, for d input parameters, entanglement can yield a factor O(d) improvement in mean squared error when estimating an analytic function of these parameters. We show that the protocol is optimal for qubit sensors, and conjecture an optimal protocol for photons passing through interferometers. Our protocol is also applicable to continuous variable measurements, such as one quadrature of a field operator. We outline a few potential applications, including calibration of laser operations in trapped ion quantum computing.

1 aQian, Kevin1 aEldredge, Zachary1 aGe, Wenchao1 aPagano, Guido1 aMonroe, Christopher1 aPorto, James, V.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1901.0904201480nas a2200193 4500008004100000245009000041210006900131260001400200490000800214520086300222100002601085700003101111700002301142700002501165700002001190700002101210700001801231856003701249 2019 eng d00aInterference of Temporally Distinguishable Photons Using Frequency-Resolved Detection0 aInterference of Temporally Distinguishable Photons Using Frequen c9/24/20190 v1233 a

We demonstrate quantum interference of three photons that are distinguishable in time, by resolving them in the conjugate parameter, frequency. We show that the multiphoton interference pattern in our setup can be manipulated by tuning the relative delays between the photons, without the need for reconfiguring the optical network. Furthermore, we observe that the symmetries of our optical network and the spectral amplitude of the input photons are manifested in the interference pattern. Moreover, we demonstrate time-reversed HOM-like interference in the spectral correlations using time-bin entangled photon pairs. By adding a time-varying dispersion using a phase modulator, our setup can be used to realize dynamically reconfigurable and scalable boson sampling in the time domain as well as frequency-resolved multiboson correlation sampling.

1 aOrre, Venkata, Vikram1 aGoldschmidt, Elizabeth, A.1 aDeshpande, Abhinav1 aGorshkov, Alexey, V.1 aTamma, Vincenzo1 aHafezi, Mohammad1 aMittal, Sunil uhttps://arxiv.org/abs/1904.0322202137nas a2200133 4500008004100000245009800041210006900139260001400208520167400222100001801896700002501914700002701939856003701966 2019 eng d00aOn the nature of the non-equilibrium phase transition in the non-Markovian driven Dicke model0 anature of the nonequilibrium phase transition in the nonMarkovia c2019/10/93 a

The Dicke model famously exhibits a phase transition to a superradiant phase with a macroscopic population of photons and is realized in multiple settings in open quantum systems. In this work, we study a variant of the Dicke model where the cavity mode is lossy due to the coupling to a Markovian environment while the atomic mode is coupled to a colored bath. We analytically investigate this model by inspecting its low-frequency behavior via the Schwinger-Keldysh field theory and carefully examine the nature of the corresponding superradiant phase transition. Integrating out the fast modes, we can identify a simple effective theory allowing us to derive analytical expressions for various critical exponents, including those, such as the dynamical critical exponent, that have not been previously considered. We find excellent agreement with previous numerical results when the non-Markovian bath is at zero temperature; however, contrary to these studies, our low-frequency approach reveals that the same exponents govern the critical behavior when the colored bath is at finite temperature unless the chemical potential is zero. Furthermore, we show that the superradiant phase transition is classical in nature, while it is genuinely non-equilibrium. We derive a fractional Langevin equation and conjecture the associated fractional Fokker-Planck equation that capture the system's long-time memory as well as its non-equilibrium behavior. Finally, we consider finite-size effects at the phase transition and identify the finite-size scaling exponents, unlocking a rich behavior in both statics and dynamics of the photonic and atomic observables.

1 aLundgren, Rex1 aGorshkov, Alexey, V.1 aMaghrebi, Mohammad, F. uhttps://arxiv.org/abs/1910.0431901912nas a2200265 4500008004100000245007900041210006900120260001500189520117500204100001601379700001501395700001201410700001501422700002001437700001101457700001301468700001901481700002001500700001701520700001501537700001701552700002501569700001501594856003701609 2019 eng d00aObservation of Domain Wall Confinement and Dynamics in a Quantum Simulator0 aObservation of Domain Wall Confinement and Dynamics in a Quantum c12/23/20193 a

Confinement is a ubiquitous mechanism in nature, whereby particles feel an attractive force that increases without bound as they separate. A prominent example is color confinement in particle physics, in which baryons and mesons are produced by quark confinement. Analogously, confinement can also occur in low-energy quantum many-body systems when elementary excitations are confined into bound quasiparticles. Here, we report the first observation of magnetic domain wall confinement in interacting spin chains with a trapped-ion quantum simulator. By measuring how correlations spread, we show that confinement can dramatically suppress information propagation and thermalization in such many-body systems. We are able to quantitatively determine the excitation energy of domain wall bound states from non-equilibrium quench dynamics. Furthermore, we study the number of domain wall excitations created for different quench parameters, in a regime that is difficult to model with classical computers. This work demonstrates the capability of quantum simulators for investigating exotic high-energy physics phenomena, such as quark collision and string breaking

1 aTan, W., L.1 aBecker, P.1 aLiu, F.1 aPagano, G.1 aCollins, K., S.1 aDe, A.1 aFeng, L.1 aKaplan, H., B.1 aKyprianidis, A.1 aLundgren, R.1 aMorong, W.1 aWhitsitt, S.1 aGorshkov, Alexey, V.1 aMonroe, C. uhttps://arxiv.org/abs/1912.1111702010nas a2200409 4500008004100000245006800041210006600109260001500175520084400190100001901034700002601053700002001079700002001099700002001119700001701139700002501156700002201181700001901203700001701222700002201239700002101261700002501282700001901307700002301326700001801349700001901367700002101386700002101407700001501428700002001443700002401463700001801487700002301505700001901528700001601547856003701563 2019 eng d00aOpportunities for Nuclear Physics & Quantum Information Science0 aOpportunities for Nuclear Physics Quantum Information Science c03/13/20193 a

his whitepaper is an outcome of the workshop Intersections between Nuclear Physics and Quantum Information held at Argonne National Laboratory on 28-30 March 2018 [www.phy.anl.gov/npqi2018/]. The workshop brought together 116 national and international experts in nuclear physics and quantum information science to explore opportunities for the two fields to collaborate on topics of interest to the U.S. Department of Energy (DOE) Office of Science, Office of Nuclear Physics, and more broadly to U.S. society and industry. The workshop consisted of 22 invited and 10 contributed talks, as well as three panel discussion sessions. Topics discussed included quantum computation, quantum simulation, quantum sensing, nuclear physics detectors, nuclear many-body problem, entanglement at collider energies, and lattice gauge theories.

1 aCloët, I., C.1 aDietrich, Matthew, R.1 aArrington, John1 aBazavov, Alexei1 aBishof, Michael1 aFreese, Adam1 aGorshkov, Alexey, V.1 aGrassellino, Anna1 aHafidi, Kawtar1 aJacob, Zubin1 aMcGuigan, Michael1 aMeurice, Yannick1 aMeziani, Zein-Eddine1 aMueller, Peter1 aMuschik, Christine1 aOsborn, James1 aOtten, Matthew1 aPetreczky, Peter1 aPolakovic, Tomas1 aPoon, Alan1 aPooser, Raphael1 aRoggero, Alessandro1 aSaffman, Mark1 aVanDevender, Brent1 aZhang, Jiehang1 aZohar, Erez uhttps://arxiv.org/abs/1903.0545301481nas a2200157 4500008004100000245006800041210006700109260001500176300001000191490000800201520102300209100002101232700001601253700001701269856003701286 2019 eng d00aParallel Self-Testing of the GHZ State with a Proof by Diagrams0 aParallel SelfTesting of the GHZ State with a Proof by Diagrams c01/29/2019 a43-660 v2873 a

Quantum self-testing addresses the following question: is it possible to verify the existence of a multipartite state even when one's measurement devices are completely untrusted? This problem has seen abundant activity in the last few years, particularly with the advent of parallel self-testing (i.e., testing several copies of a state at once), which has applications not only to quantum cryptography but also quantum computing. In this work we give the first error-tolerant parallel self-test in a three-party (rather than two-party) scenario, by showing that an arbitrary number of copies of the GHZ state can be self-tested. In order to handle the additional complexity of a three-party setting, we use a diagrammatic proof based on categorical quantum mechanics, rather than a typical symbolic proof. The diagrammatic approach allows for manipulations of the complicated tensor networks that arise in the proof, and gives a demonstration of the importance of picture-languages in quantum information.

1 aBreiner, Spencer1 aKalev, Amir1 aMiller, Carl uhttps://arxiv.org/abs/1806.0474401707nas a2200133 4500008004100000245006500041210006500106260001500171490000800186520130600194100001701500700001901517856003701536 2019 eng d00aProduct Spectrum Ansatz and the Simplicity of Thermal States0 aProduct Spectrum Ansatz and the Simplicity of Thermal States c2019/11/180 v1003 a

Calculating the physical properties of quantum thermal states is a difficult problem for classical computers, rendering it intractable for most quantum many-body systems. A quantum computer, by contrast, would make many of these calculations feasible in principle, but it is still non-trivial to prepare a given thermal state or sample from it. It is also not known how to prepare special simple purifications of thermal states known as thermofield doubles, which play an important role in quantum many-body physics and quantum gravity. To address this problem, we propose a variational scheme to prepare approximate thermal states on a quantum computer by applying a series of two-qubit gates to a product mixed state. We apply our method to a non-integrable region of the mixed field Ising chain and the Sachdev-Ye-Kitaev model. We also demonstrate how our method can be easily extended to large systems governed by local Hamiltonians and the preparation of thermofield double states. By comparing our results with exact solutions, we find that our construction enables the efficient preparation of approximate thermal states on quantum devices. Our results can be interpreted as implying that the details of the many-body energy spectrum are not needed to capture simple thermal observables.

1 aMartyn, John1 aSwingle, Brian uhttps://arxiv.org/abs/1812.0101501709nas a2200241 4500008004100000245007100041210006900112260001500181520103600196100001501232700002101247700001801268700001801286700002501304700001301329700001401342700001201356700001501368700001701383700001401400700001601414856003701430 2019 eng d00aProgrammable Quantum Simulations of Spin Systems with Trapped Ions0 aProgrammable Quantum Simulations of Spin Systems with Trapped Io c12/17/20193 a

Laser-cooled and trapped atomic ions form an ideal standard for the simulation of interacting quantum spin models. Effective spins are represented by appropriate internal energy levels within each ion, and the spins can be measured with near-perfect efficiency using state-dependent fluorescence techniques. By applying optical fields that exert optical dipole forces on the ions, their Coulomb interaction can be modulated in ways that give rise to long-range and tunable spin-spin interactions that can be reconfigured by shaping the spectrum and pattern of the laser fields. Here we review the theoretical mapping of atomic ions to interacting spin systems, the experimental preparation of complex equilibrium states, and the study of dynamical processes of this many-body interacting quantum system. The use of such quantum simulators for studying spin models may inform our understanding of exotic quantum materials and shed light on interacting quantum systems that cannot be modeled with conventional computers. 

1 aMonroe, C.1 aCampbell, W., C.1 aDuan, L., -M.1 aGong, Z., -X.1 aGorshkov, Alexey, V.1 aHess, P.1 aIslam, R.1 aKim, K.1 aPagano, G.1 aRicherme, P.1 aSenko, C.1 aYao, N., Y. uhttps://arxiv.org/abs/1912.0784501764nas a2200289 4500008004100000245007400041210006900115260001500184520095900199100001501158700001401173700001501187700002001202700001101222700001701233700001901250700002001269700001601289700002901305700001801334700001801352700001201370700001501382700002501397700001501422856003701437 2019 eng d00aQuantum Approximate Optimization with a Trapped-Ion Quantum Simulator0 aQuantum Approximate Optimization with a TrappedIon Quantum Simul c06/06/20193 a

Quantum computers and simulators may offer significant advantages over their classical counterparts, providing insights into quantum many-body systems and possibly solving exponentially hard problems, such as optimization and satisfiability. Here we report the first implementation of a shallow-depth Quantum Approximate Optimization Algorithm (QAOA) using an analog quantum simulator to estimate the ground state energy of the transverse field Ising model with tunable long-range interactions. First, we exhaustively search the variational control parameters to approximate the ground state energy with up to 40 trapped-ion qubits. We then interface the quantum simulator with a classical algorithm to more efficiently find the optimal set of parameters that minimizes the resulting energy of the system. We finally sample from the full probability distribution of the QAOA output with single-shot and efficient measurements of every qubit. 

1 aPagano, G.1 aBapat, A.1 aBecker, P.1 aCollins, K., S.1 aDe, A.1 aHess, P., W.1 aKaplan, H., B.1 aKyprianidis, A.1 aTan, W., L.1 aBaldwin, Christopher, L.1 aBrady, L., T.1 aDeshpande, A.1 aLiu, F.1 aJordan, S.1 aGorshkov, Alexey, V.1 aMonroe, C. uhttps://arxiv.org/abs/1906.0270001947nas a2200397 4500008004100000245005400041210005400095260001500149520085000164100001801014700001601032700002301048700002301071700002201094700002401116700001901140700001801159700001801177700002001195700002501215700001801240700001801258700001901276700001901295700001601314700002301330700001901353700001701372700002401389700001901413700002201432700001901454700001901473700002001492856003701512 2019 eng d00aQuantum Computer Systems for Scientific Discovery0 aQuantum Computer Systems for Scientific Discovery c12/16/20193 a

The great promise of quantum computers comes with the dual challenges of building them and finding their useful applications. We argue that these two challenges should be considered together, by co-designing full stack quantum computer systems along with their applications in order to hasten their development and potential for scientific discovery. In this context, we identify scientific and community needs, opportunities, and significant challenges for the development of quantum computers for science over the next 2-10 years. This document is written by a community of university, national laboratory, and industrial researchers in the field of Quantum Information Science and Technology, and is based on a summary from a U.S. National Science Foundation workshop on Quantum Computing held on October 21-22, 2019 in Alexandria, VA.

1 aAlexeev, Yuri1 aBacon, Dave1 aBrown, Kenneth, R.1 aCalderbank, Robert1 aCarr, Lincoln, D.1 aChong, Frederic, T.1 aDeMarco, Brian1 aEnglund, Dirk1 aFarhi, Edward1 aFefferman, Bill1 aGorshkov, Alexey, V.1 aHouck, Andrew1 aKim, Jungsang1 aKimmel, Shelby1 aLange, Michael1 aLloyd, Seth1 aLukin, Mikhail, D.1 aMaslov, Dmitri1 aMaunz, Peter1 aMonroe, Christopher1 aPreskill, John1 aRoetteler, Martin1 aSavage, Martin1 aThompson, Jeff1 aVazirani, Umesh uhttps://arxiv.org/abs/1912.0757702574nas a2200313 4500008004100000245006200041210006200103260001500165520165200180100002401832700002201856700002001878700002201898700002001920700002701940700002201967700002401989700001802013700002102031700002102052700001702073700003102090700001902121700002002140700001902160700002302179700002102202856003702223 2019 eng d00aQuantum Computing at the Frontiers of Biological Sciences0 aQuantum Computing at the Frontiers of Biological Sciences c2019/11/163 a

The search for meaningful structure in biological data has relied on cutting-edge advances in computational technology and data science methods. However, challenges arise as we push the limits of scale and complexity in biological problems. Innovation in massively parallel, classical computing hardware and algorithms continues to address many of these challenges, but there is a need to simultaneously consider new paradigms to circumvent current barriers to processing speed. Accordingly, we articulate a view towards quantum computation and quantum information science, where algorithms have demonstrated potential polynomial and exponential computational speedups in certain applications, such as machine learning. The maturation of the field of quantum computing, in hardware and algorithm development, also coincides with the growth of several collaborative efforts to address questions across length and time scales, and scientific disciplines. We use this coincidence to explore the potential for quantum computing to aid in one such endeavor: the merging of insights from genetics, genomics, neuroimaging and behavioral phenotyping. By examining joint opportunities for computational innovation across fields, we highlight the need for a common language between biological data analysis and quantum computing. Ultimately, we consider current and future prospects for the employment of quantum computing algorithms in the biological sciences. 

1 aEmani, Prashant, S.1 aWarrell, Jonathan1 aAnticevic, Alan1 aBekiranov, Stefan1 aGandal, Michael1 aMcConnell, Michael, J.1 aSapiro, Guillermo1 aAspuru-Guzik, Alán1 aBaker, Justin1 aBastiani, Matteo1 aMcClure, Patrick1 aMurray, John1 aSotiropoulos, Stamatios, N1 aTaylor, J., M.1 aSenthil, Geetha1 aLehner, Thomas1 aGerstein, Mark, B.1 aHarrow, Aram, W. uhttps://arxiv.org/abs/1911.0712701711nas a2200181 4500008004100000245005600041210005600097260001500153490000700168520117600175100002301351700002701374700002101401700001701422700002401439700002901463856003701492 2019 eng d00aQuantum repeaters based on two species trapped ions0 aQuantum repeaters based on two species trapped ions c05/02/20190 v213 a

We examine the viability of quantum repeaters based on two-species trapped ion modules for long distance quantum key distribution. Repeater nodes comprised of ion-trap modules of co-trapped ions of distinct species are considered. The species used for communication qubits has excellent optical properties while the other longer lived species serves as a memory qubit in the modules. Each module interacts with the network only via single photons emitted by the communication ions. Coherent Coulomb interaction between ions is utilized to transfer quantum information between the communication and memory ions and to achieve entanglement swapping between two memory ions. We describe simple modular quantum repeater architectures realizable with the ion-trap modules and numerically study the dependence of the quantum key distribution rate on various experimental parameters, including coupling efficiency, gate infidelity, operation time and length of the elementary links. Our analysis suggests crucial improvements necessary in a physical implementation for co-trapped two-species ions to be a competitive platform in long-distance quantum communication. 

1 aSantra, Siddhartha1 aMuralidharan, Sreraman1 aLichtman, Martin1 aJiang, Liang1 aMonroe, Christopher1 aMalinovsky, Vladimir, S. uhttps://arxiv.org/abs/1811.1072302892nas a2200397 4500008004100000245005600041210005500097260001500152520177700167100001701944700002301961700002101984700002202005700001902027700001602046700001902062700002502081700002302106700002002129700002002149700002602169700002302195700002402218700002202242700002302264700001602287700001302303700002002316700002402336700001702360700001902377700001802396700002302414700002002437856003702457 2019 eng d00aQuantum Simulators: Architectures and Opportunities0 aQuantum Simulators Architectures and Opportunities c12/14/20193 a

Quantum simulators are a promising technology on the spectrum of quantum devices from specialized quantum experiments to universal quantum computers. These quantum devices utilize entanglement and many-particle behaviors to explore and solve hard scientific, engineering, and computational problems. Rapid development over the last two decades has produced more than 300 quantum simulators in operation worldwide using a wide variety of experimental platforms. Recent advances in several physical architectures promise a golden age of quantum simulators ranging from highly optimized special purpose simulators to flexible programmable devices. These developments have enabled a convergence of ideas drawn from fundamental physics, computer science, and device engineering. They have strong potential to address problems of societal importance, ranging from understanding vital chemical processes, to enabling the design of new materials with enhanced performance, to solving complex computational problems. It is the position of the community, as represented by participants of the NSF workshop on "Programmable Quantum Simulators," that investment in a national quantum simulator program is a high priority in order to accelerate the progress in this field and to result in the first practical applications of quantum machines. Such a program should address two areas of emphasis: (1) support for creating quantum simulator prototypes usable by the broader scientific community, complementary to the present universal quantum computer effort in industry; and (2) support for fundamental research carried out by a blend of multi-investigator, multi-disciplinary collaborations with resources for quantum simulator software, hardware, and education. 

1 aAltman, Ehud1 aBrown, Kenneth, R.1 aCarleo, Giuseppe1 aCarr, Lincoln, D.1 aDemler, Eugene1 aChin, Cheng1 aDeMarco, Brian1 aEconomou, Sophia, E.1 aEriksson, Mark, A.1 aFu, Kai-Mei, C.1 aGreiner, Markus1 aHazzard, Kaden, R. A.1 aHulet, Randall, G.1 aKollár, Alicia, J.1 aLev, Benjamin, L.1 aLukin, Mikhail, D.1 aMa, Ruichao1 aMi, Xiao1 aMisra, Shashank1 aMonroe, Christopher1 aMurch, Kater1 aNazario, Zaira1 aNi, Kang-Kuen1 aPotter, Andrew, C.1 aRoushan, Pedram uhttps://arxiv.org/abs/1912.0693801623nas a2200133 4500008004100000245011100041210006900152260001400221520114300235100002601378700002401404700002401428856003701452 2019 eng d00aSite-by-site quantum state preparation algorithm for preparing vacua of fermionic lattice field theories 0 aSitebysite quantum state preparation algorithm for preparing vac c2019/11/83 a

Answering whether quantum computers can efficiently simulate quantum field theories has both theoretical and practical motivation. From the theoretical point of view, it answers the question of whether a hypothetical computer that utilizes quantum field theory would be more powerful than other quantum computers. From the practical point of view, when reliable quantum computers are eventually built, these algorithms can help us better understand the underlying physics that govern our world. In the best known quantum algorithms for simulating quantum field theories, the time scaling is dominated by initial state preparation. In this paper, we exclusively focus on state preparation and present a heuristic algorithm that can prepare the vacuum of fermionic systems in more general cases and more efficiently than previous methods. With our method, state preparation is no longer the bottleneck, as its runtime has the same asymptotic scaling with the desired precision as the remainder of the simulation algorithm. We numerically demonstrate the effectiveness of our proposed method for the 1+1 dimensional Gross-Neveu model.

1 aMoosavian, Ali, Hamed1 aGarrison, James, R.1 aJordan, Stephen, P. uhttps://arxiv.org/abs/1911.0350502754nas a2200229 4500008004100000245009900041210006900140520205300209100001902262700002402281700001302305700001502318700001302333700001702346700001402363700001602377700001602393700001702409700001902426700001602445856006302461 2019 eng d00aStatus Report on the First Round of the NIST Post-Quantum Cryptography Standardization Process0 aStatus Report on the First Round of the NIST PostQuantum Cryptog3 a

The National Institute of Standards and Technology is in the process of selecting one or more
public-key cryptographic algorithms through a public competition-like process. The new publickey cryptography standards will specify one or more additional digital signature, public-key
encryption, and key-establishment algorithms to augment FIPS 186-4, Digital Signature Standard
(DSS), as well as special publications SP 800-56A Revision 2, Recommendation for Pair-Wise
Key Establishment Schemes Using Discrete Logarithm Cryptography, and SP 800-56B,
Recommendation for Pair-Wise Key-Establishment Schemes Using Integer Factorization. It is
intended that these algorithms will be capable of protecting sensitive information well into the
foreseeable future, including after the advent of quantum computers.
In November 2017, 82 candidate algorithms were submitted to NIST for consideration. Among
these, 69 met both the minimum acceptance criteria and our submission requirements, and were
accepted as First-Round Candidates on Dec. 20, 2017, marking the beginning of the First Round
of the NIST Post-Quantum Cryptography Standardization Process. This report describes the
evaluation criteria and selection process, based on public feedback and internal review of the
first-round candidates, and summarizes the 26 candidate algorithms announced on January 30,
2019 for moving forward to the second round of the competition. The 17 Second-Round
Candidate public-key encryption and key-establishment algorithms are BIKE, Classic McEliece,
CRYSTALS-KYBER, FrodoKEM, HQC, LAC, LEDAcrypt (merger of LEDAkem/LEDApkc),
NewHope, NTRU (merger of NTRUEncrypt/NTRU-HRSS-KEM), NTRU Prime, NTS-KEM,
ROLLO (merger of LAKE/LOCKER/Ouroboros-R), Round5 (merger of Hila5/Round2), RQC,
SABER, SIKE, and Three Bears. The 9 Second-Round Candidates for digital signatures are
CRYSTALS-DILITHIUM, FALCON, GeMSS, LUOV, MQDSS, Picnic, qTESLA, Rainbow,
and SPHINCS+.

1 aAlagic, Gorjan1 aAlperin-Sheriff, J.1 aApon, D.1 aCooper, D.1 aDang, Q.1 aMiller, Carl1 aMoody, D.1 aPeralta, R.1 aPerlner, R.1 aRobinson, A.1 aSmith-Tone, D.1 aLiu, Yi-Kai uhttps://nvlpubs.nist.gov/nistpubs/ir/2019/NIST.IR.8240.pdf01624nas a2200193 4500008004100000245009000041210006900131260001500200520100400215100001701219700002401236700001801260700001601278700002301294700002401317700002401341700002801365856003701393 2019 eng d00aToward convergence of effective field theory simulations on digital quantum computers0 aToward convergence of effective field theory simulations on digi c04/18/20193 a

We report results for simulating an effective field theory to compute the binding energy of the deuteron nucleus using a hybrid algorithm on a trapped-ion quantum computer. Two increasingly complex unitary coupled-cluster ansaetze have been used to compute the binding energy to within a few percent for successively more complex Hamiltonians. By increasing the complexity of the Hamiltonian, allowing more terms in the effective field theory expansion and calculating their expectation values, we present a benchmark for quantum computers based on their ability to scalably calculate the effective field theory with increasing accuracy. Our result of E4=−2.220±0.179MeV may be compared with the exact Deuteron ground-state energy −2.224MeV. We also demonstrate an error mitigation technique using Richardson extrapolation on ion traps for the first time. The error mitigation circuit represents a record for deepest quantum circuit on a trapped-ion quantum computer. 

1 aShehab, Omar1 aLandsman, Kevin, A.1 aNam, Yunseong1 aZhu, Daiwei1 aLinke, Norbert, M.1 aKeesan, Matthew, J.1 aPooser, Raphael, C.1 aMonroe, Christopher, R. uhttps://arxiv.org/abs/1904.0433801499nas a2200193 4500008004100000245007800041210006900119260001500188520089900203100002401102700001401126700002101140700001601161700002301177700002301200700001701223700002801240856003701268 2019 eng d00aTwo-qubit entangling gates within arbitrarily long chains of trapped ions0 aTwoqubit entangling gates within arbitrarily long chains of trap c05/28/20193 a

Ion trap systems are a leading platform for large scale quantum computers. Trapped ion qubit crystals are fully-connected and reconfigurable, owing to their long range Coulomb interaction that can be modulated with external optical forces. However, the spectral crowding of collective motional modes could pose a challenge to the control of such interactions for large numbers of qubits. Here, we show that high-fidelity quantum gate operations are still possible with very large trapped ion crystals, simplifying the scaling of ion trap quantum computers. To this end, we present analytical work that determines how parallel entangling gates produce a crosstalk error that falls off as the inverse cube of the distance between the pairs. We also show experimental work demonstrating entangling gates on a fully-connected chain of seventeen 171Yb+ ions with fidelities as high as 97(1)%.

1 aLandsman, Kevin, A.1 aWu, Yukai1 aLeung, Pak, Hong1 aZhu, Daiwei1 aLinke, Norbert, M.1 aBrown, Kenneth, R.1 aDuan, Luming1 aMonroe, Christopher, R. uhttps://arxiv.org/abs/1905.1042100403nas a2200121 4500008004100000245006400041210006400105260001500169100002000184700002100204700001900225856003700244 2019 eng d00aUniversal Constraints on Energy Flow and SYK Thermalization0 aUniversal Constraints on Energy Flow and SYK Thermalization c12/10/20191 aAlmheiri, Ahmed1 aMilekhin, Alexey1 aSwingle, Brian uhttps://arxiv.org/abs/1912.0491201295nas a2200169 4500008004100000245008000041210006900121260001500190490000600205520078500211100001800996700001901014700001301033700002301046700001901069856003701088 2018 eng d00aAutomated optimization of large quantum circuits with continuous parameters0 aAutomated optimization of large quantum circuits with continuous c2017/10/190 v43 a

We develop and implement automated methods for optimizing quantum circuits of the size and type expected in quantum computations that outperform classical computers. We show how to handle continuous gate parameters and report a collection of fast algorithms capable of optimizing large-scale quantum circuits. For the suite of benchmarks considered, we obtain substantial reductions in gate counts. In particular, we provide better optimization in significantly less time than previous approaches, while making minimal structural changes so as to preserve the basic layout of the underlying quantum algorithms. Our results help bridge the gap between the computations that can be run on existing hardware and those that are expected to outperform classical computers. 

1 aNam, Yunseong1 aRoss, Neil, J.1 aSu, Yuan1 aChilds, Andrew, M.1 aMaslov, Dmitri uhttps://arxiv.org/abs/1710.0734501296nas a2200157 4500008004100000245005600041210005600097260001500153520081900168100001900987700002801006700002101034700002601055700002001081856003701101 2018 eng d00aBell monogamy relations in arbitrary qubit networks0 aBell monogamy relations in arbitrary qubit networks c2018/01/093 a

Characterizing trade-offs between simultaneous violations of multiple Bell inequalities in a large network of qubits is computationally demanding. We propose a graph-theoretic approach to efficiently produce Bell monogamy relations in arbitrary arrangements of qubits. All the relations obtained for bipartite Bell inequalities are tight and leverage only a single Bell monogamy relation. This feature is unique to bipartite Bell inequalities, as we show that there is no finite set of such elementary monogamy relations for multipartite inequalities. Nevertheless, many tight monogamy relations for multipartite inequalities can be obtained with our method as shown in explicit examples.

1 aTran, Minh, C.1 aRamanathan, Ravishankar1 aMcKague, Matthew1 aKaszlikowski, Dagomir1 aPaterek, Tomasz uhttps://arxiv.org/abs/1801.0307101523nas a2200205 4500008004100000245004800041210004500089260001500134300001200149490000800161520099800169100001101167700001501178700001301193700001801206700001901224700001901243700001801262856003701280 2018 eng d00aA Coherent Spin-Photon Interface in Silicon0 aCoherent SpinPhoton Interface in Silicon c2018/03/29 a599-6030 v5553 a

Electron spins in silicon quantum dots are attractive systems for quantum computing due to their long coherence times and the promise of rapid scaling using semiconductor fabrication techniques. While nearest neighbor exchange coupling of two spins has been demonstrated, the interaction of spins via microwave frequency photons could enable long distance spin-spin coupling and "all-to-all" qubit connectivity. Here we demonstrate strong-coupling between a single spin in silicon and a microwave frequency photon with spin-photon coupling rates g_s/(2π) > 10 MHz. The mechanism enabling coherent spin-photon interactions is based on spin-charge hybridization in the presence of a magnetic field gradient. In addition to spin-photon coupling, we demonstrate coherent control of a single spin in the device and quantum non-demolition spin state readout using cavity photons. These results open a direct path toward entangling single spins using microwave frequency photons.

1 aMi, X.1 aBenito, M.1 aPutz, S.1 aZajac, D., M.1 aTaylor, J., M.1 aBurkard, Guido1 aPetta, J., R. uhttps://arxiv.org/abs/1710.0326501974nas a2200181 4500008004100000245005000041210004800091260001500139520145800154100001101612700001501623700001301638700001801651700001901669700001901688700001801707856006701725 2018 eng d00aA coherent spin–photon interface in silicon0 acoherent spin–photon interface in silicon c2018/02/143 a

Electron spins in silicon quantum dots are attractive systems for quantum computing owing to their long coherence times and the promise of rapid scaling of the number of dots in a system using semiconductor fabrication techniques. Although nearest-neighbour exchange coupling of two spins has been demonstrated, the interaction of spins via microwave-frequency photons could enable long-distance spin–spin coupling and connections between arbitrary pairs of qubits (‘all-to-all’ connectivity) in a spin-based quantum processor. Realizing coherent spin–photon coupling is challenging because of the small magnetic-dipole moment of a single spin, which limits magnetic-dipole coupling rates to less than 1 kilohertz. Here we demonstrate strong coupling between a single spin in silicon and a single microwave-frequency photon, with spin–photon coupling rates of more than 10 megahertz. The mechanism that enables the coherent spin–photon interactions is based on spin–charge hybridization in the presence of a magnetic-field gradient. In addition to spin–photon coupling, we demonstrate coherent control and dispersive readout of a single spin. These results open up a direct path to entangling single spins using microwave-frequency photons.

1 aMi, X.1 aBenito, M.1 aPutz, S.1 aZajac, D., M.1 aTaylor, J., M.1 aBurkard, Guido1 aPetta, J., R. uhttps://www.nature.com/articles/nature25769#author-information01463nas a2200229 4500008004100000245006800041210006700109520082000176100001500996700001701011700001901028700001601047700001701063700001501080700002001095700001401115700001901129700002201148700001101170700001501181856003701196 2018 eng d00aCryogenic Trapped-Ion System for Large Scale Quantum Simulation0 aCryogenic TrappedIon System for Large Scale Quantum Simulation3 a

We present a cryogenic ion trapping system designed for large scale quantum simulation of spin models. Our apparatus is based on a segmented-blade ion trap enclosed in a 4 K cryostat, which enables us to routinely trap over 100 171Yb+ ions in a linear configuration for hours due to a low background gas pressure from differential cryo-pumping. We characterize the cryogenic vacuum by using trapped ion crystals as a pressure gauge, measuring both inelastic and elastic collision rates with the molecular background gas. We demonstrate nearly equidistant ion spacing for chains of up to 44 ions using anharmonic axial potentials. This reliable production and lifetime enhancement of large linear ion chains will enable quantum simulation of spin models that are intractable with classical computer modelling.

1 aPagano, G.1 aHess, P., W.1 aKaplan, H., B.1 aTan, W., L.1 aRicherme, P.1 aBecker, P.1 aKyprianidis, A.1 aZhang, J.1 aBirckelbaw, E.1 aHernandez, M., R.1 aWu, Y.1 aMonroe, C. uhttps://arxiv.org/abs/1802.0311801552nas a2200169 4500008004100000245007500041210006900116520100400185100001901189700002301208700002201231700002401253700002401277700002001301700002401321856003701345 2018 eng d00aDemonstration of Bayesian quantum game on an ion trap quantum computer0 aDemonstration of Bayesian quantum game on an ion trap quantum co3 a

We demonstrate a Bayesian quantum game on an ion trap quantum computer with five qubits. The players share an entangled pair of qubits and perform rotations on their qubit as the strategy choice. Two five-qubit circuits are sufficient to run all 16 possible strategy choice sets in a game with four possible strategies. The data are then parsed into player types randomly in order to combine them classically into a Bayesian framework. We exhaustively compute the possible strategies of the game so that the experimental data can be used to solve for the Nash equilibria of the game directly. Then we compare the payoff at the Nash equilibria and location of phase-change-like transitions obtained from the experimental data to the theory, and study how it changes as a function of the amount of entanglement.

1 aSolmeyer, Neal1 aLinke, Norbert, M.1 aFiggatt, Caroline1 aLandsman, Kevin, A.1 aBalu, Radhakrishnan1 aSiopsis, George1 aMonroe, Christopher uhttps://arxiv.org/abs/1802.0811601752nas a2200169 4500008004100000245007800041210006900119260001500188300001100203490000700214520121000221100002201431700002101453700002401474700001501498856006901513 2018 eng d00aDiffusion Monte Carlo Versus Adiabatic Computation for Local Hamiltonians0 aDiffusion Monte Carlo Versus Adiabatic Computation for Local Ham c2018/02/15 a0223230 v973 a

Most research regarding quantum adiabatic optimization has focused on stoquastic Hamiltonians, whose ground states can be expressed with only real, nonnegative amplitudes. This raises the question of whether classical Monte Carlo algorithms can efficiently simulate quantum adiabatic optimization with stoquastic Hamiltonians. Recent results have given counterexamples in which path integral and diffusion Monte Carlo fail to do so. However, most adiabatic optimization algorithms, such as for solving MAX-k-SAT problems, use k-local Hamiltonians, whereas our previous counterexample for diffusion Monte Carlo involved n-body interactions. Here we present a new 6-local counterexample which demonstrates that even for these local Hamiltonians there are cases where diffusion Monte Carlo cannot efficiently simulate quantum adiabatic optimization. Furthermore, we perform empirical testing of diffusion Monte Carlo on a standard well-studied class of permutation-symmetric tunneling problems and similarly find large advantages for quantum optimization over diffusion Monte Carlo.

1 aBringewatt, Jacob1 aDorland, William1 aJordan, Stephen, P.1 aMink, Alan uhttps://journals.aps.org/pra/abstract/10.1103/PhysRevA.97.02232303349nas a2200217 4500008004100000245008400041210006900125260001500194300001100209490000700220520266700227100002202894700002002916700001702936700003102953700002102984700002403005700002103029700002503050856005603075 2018 eng d00aDissipation induced dipole blockade and anti-blockade in driven Rydberg systems0 aDissipation induced dipole blockade and antiblockade in driven R c2018/02/28 a0234240 v973 a

We study theoretically and experimentally the competing blockade and antiblockade effects induced by spontaneously generated contaminant Rydberg atoms in driven Rydberg systems. These contaminant atoms provide a source of strong dipole-dipole interactions and play a crucial role in the system's behavior. We study this problem theoretically using two different approaches. The first is a cumulant expansion approximation, in which we ignore third-order and higher connected correlations. Using this approach for the case of resonant drive, a many-body blockade radius picture arises, and we find qualitative agreement with previous experimental results. We further predict that as the atomic density is increased, the Rydberg population's dependence on Rabi frequency will transition from quadratic to linear dependence at lower Rabi frequencies. We study this behavior experimentally by observing this crossover at two different atomic densities. We confirm that the larger density system has a smaller crossover Rabi frequency than the smaller density system. The second theoretical approach is a set of phenomenological inhomogeneous rate equations. We compare the results of our rate-equation model to the experimental observations [E. A. Goldschmidt et al.Phys. Rev. Lett. 116, 113001 (2016)] and find that these rate equations provide quantitatively good scaling behavior of the steady-state Rydberg population for both resonant and off-resonant drives.

1 aYoung, Jeremy, T.1 aBoulier, Thomas1 aMagnan, Eric1 aGoldschmidt, Elizabeth, A.1 aWilson, Ryan, M.1 aRolston, Steven, L.1 aPorto, James, V.1 aGorshkov, Alexey, V. uhttps://link.aps.org/doi/10.1103/PhysRevA.97.02342402638nas a2200265 4500008004100000245009500041210006900136260001500205300001200220490000800232520186000240100002102100700001902121700001802140700001802158700001502176700002002191700001902211700001602230700002502246700001802271700002402289700002202313856003702335 2018 eng d00aExperimentally Generated Randomness Certified by the Impossibility of Superluminal Signals0 aExperimentally Generated Randomness Certified by the Impossibili c2018/04/11 a223-2260 v5563 a

From dice to modern complex circuits, there have been many attempts to build increasingly better devices to generate random numbers. Today, randomness is fundamental to security and cryptographic systems, as well as safeguarding privacy. A key challenge with random number generators is that it is hard to ensure that their outputs are unpredictable. For a random number generator based on a physical process, such as a noisy classical system or an elementary quantum measurement, a detailed model describing the underlying physics is required to assert unpredictability. Such a model must make a number of assumptions that may not be valid, thereby compromising the integrity of the device. However, it is possible to exploit the phenomenon of quantum nonlocality with a loophole-free Bell test to build a random number generator that can produce output that is unpredictable to any adversary limited only by general physical principles. With recent technological developments, it is now possible to carry out such a loophole-free Bell test. Here we present certified randomness obtained from a photonic Bell experiment and extract 1024 random bits uniform to within 10−12. These random bits could not have been predicted within any physical theory that prohibits superluminal signaling and allows one to make independent measurement choices. To certify and quantify the randomness, we describe a new protocol that is optimized for apparatuses characterized by a low per-trial violation of Bell inequalities. We thus enlisted an experimental result that fundamentally challenges the notion of determinism to build a system that can increase trust in random sources. In the future, random number generators based on loophole-free Bell tests may play a role in increasing the security and trust of our cryptographic systems and infrastructure.

1 aBierhorst, Peter1 aKnill, Emanuel1 aGlancy, Scott1 aZhang, Yanbao1 aMink, Alan1 aJordan, Stephen1 aRommal, Andrea1 aLiu, Yi-Kai1 aChristensen, Bradley1 aNam, Sae, Woo1 aStevens, Martin, J.1 aShalm, Lynden, K. uhttps://arxiv.org/abs/1803.0621901418nas a2200145 4500008004100000245007200041210006900113260001500182300001100197490000600208520097500214100002601189700002001215856003701235 2018 eng d00aFaster Quantum Algorithm to simulate Fermionic Quantum Field Theory0 aFaster Quantum Algorithm to simulate Fermionic Quantum Field The c2018/05/04 a0123320 vA3 a

In quantum algorithms discovered so far for simulating scattering processes in quantum field theories, state preparation is the slowest step. We present a new algorithm for preparing particle states to use in simulation of Fermionic Quantum Field Theory (QFT) on a quantum computer, which is based on the matrix product state ansatz. We apply this to the massive Gross-Neveu model in one spatial dimension to illustrate the algorithm, but we believe the same algorithm with slight modifications can be used to simulate any one-dimensional massive Fermionic QFT. In the case where the number of particle species is one, our algorithm can prepare particle states using O(ε−3.23…) gates, which is much faster than previous known results, namely O(ε−8−o(1)). Furthermore, unlike previous methods which were based on adiabatic state preparation, the method given here should be able to simulate quantum phases unconnected to the free theory.

1 aMoosavian, Ali, Hamed1 aJordan, Stephen uhttps://arxiv.org/abs/1711.0400601691nas a2200169 4500008004100000245007000041210006900111260001500180300001300195490000600208520118500214100002701399700001301426700001901439700002601458856003701484 2018 eng d00aFractal Universality in Near-Threshold Magnetic Lanthanide Dimers0 aFractal Universality in NearThreshold Magnetic Lanthanide Dimers c2018/02/16 aeaap83080 v43 a

Ergodic quantum systems are often quite alike, whereas nonergodic, fractal systems are unique and display characteristic properties. We explore one of these fractal systems, weakly bound dysprosium lanthanide molecules, in an external magnetic field. As recently shown, colliding ultracold magnetic dysprosium atoms display a soft chaotic behavior with a small degree of disorder. We broaden this classification by investigating the generalized inverse participation ratio and fractal dimensions for large sets of molecular wave functions. Our exact close-coupling simulations reveal a dynamic phase transition from partially localized states to totally delocalized states and universality in its distribution by increasing the magnetic field strength to only a hundred Gauss (or 10 mT). Finally, we prove the existence of nonergodic delocalized phase in the system and explain the violation of ergodicity by strong coupling between near-threshold molecular states and the nearby continuum.

1 aMakrides, Constantinos1 aLi, Ming1 aTiesinga, Eite1 aKotochigova, Svetlana uhttps://arxiv.org/abs/1802.0958601617nas a2200157 4500008004100000245012800041210006900169520105700238100001801295700002401313700002101337700001801358700002101376700002501397856003701422 2018 eng d00aFractional quantum Hall phases of bosons with tunable interactions: From the Laughlin liquid to a fractional Wigner crystal0 aFractional quantum Hall phases of bosons with tunable interactio3 a

Highly tunable platforms for realizing topological phases of matter are emerging from atomic and photonic systems, and offer the prospect of designing interactions between particles. The shape of the potential, besides playing an important role in the competition between different fractional quantum Hall phases, can also trigger the transition to symmetry-broken phases, or even to phases where topological and symmetry-breaking order coexist. Here, we explore the phase diagram of an interacting bosonic model in the lowest Landau level at half-filling as two-body interactions are tuned. Apart from the well-known Laughlin liquid, Wigner crystal phase, stripe, and bubble phases, we also find evidence of a phase that exhibits crystalline order at fractional filling per crystal site. The Laughlin liquid transits into this phase when pairs of bosons strongly repel each other at relative angular momentum 4ℏ. We show that such interactions can be achieved by dressing ground-state cold atoms with multiple different-parity Rydberg states.

1 aGraß, Tobias1 aBienias, Przemyslaw1 aGullans, Michael1 aLundgren, Rex1 aMaciejko, Joseph1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1809.0449301264nas a2200157 4500008004100000245006300041210006300104520077600167100002100943700002100964700002000985700002001005700002001025700002401045856003701069 2018 eng d00aHigh Purity Single Photons Entangled with an Atomic Memory0 aHigh Purity Single Photons Entangled with an Atomic Memory3 a

Trapped atomic ions are an ideal candidate for quantum network nodes, with long-lived identical qubit memories that can be locally entangled through their Coulomb interaction and remotely entangled through photonic channels. The integrity of this photonic interface is generally reliant on purity of single photons produced by the quantum memory. Here we demonstrate a single-photon source for quantum networking based on a trapped 138Ba+ ion with a single photon purity of g2(0)=(8.1±2.3)×10−5 without background subtraction. We further optimize the tradeoff between the photonic generation rate and the memory-photon entanglement fidelity for the case of polarization photonic qubits by tailoring the spatial mode of the collected light. 

1 aCrocker, Clayton1 aLichtman, Martin1 aSosnova, Ksenia1 aCarter, Allison1 aScarano, Sophia1 aMonroe, Christopher uhttps://arxiv.org/abs/1812.0174901727nas a2200157 4500008004100000245004800041210004700089260001500136300001100151490000700162520129200169100001701461700001901478700001601497856005601513 2018 eng d00aKeyring models: an approach to steerability0 aKeyring models an approach to steerability c2018/01/02 a0221030 v593 a

If a measurement is made on one half of a bipartite system then, conditioned on the outcome, the other half has a new reduced state. If these reduced states defy classical explanation — that is, if shared randomness cannot produce these reduced states for all possible measurements — the bipartite state is said to be steerable. Determining which states are steerable is a challenging problem even for low dimensions. In the case of two-qubit systems a criterion is known for T-states (that is, those with maximally mixed marginals) under projective measurements. In the current work we introduce the concept of keyring models — a special class of local hidden state model. When the measurements made correspond to real projectors, these allow us to study steerability beyond T-states. Using keyring models, we completely solve the steering problem for real projective measurements when the state arises from mixing a pure two-qubit state with uniform noise. We also give a partial solution in the case when the uniform noise is replaced by independent depolarizing channels. Our results imply that Werner states, which are a special case of the previous states, are unsteerable under real projective measurements if and only if their efficiency is at most 2/π.

1 aMiller, Carl1 aColbeck, Roger1 aShi, Yaoyun uhttp://aip.scitation.org/doi/full/10.1063/1.500619901139nas a2200133 4500008004100000245004700041210004600088260001200134300001100146520077800157100001600935700001700951856003700968 2018 eng d00aLocal randomness: Examples and application0 aLocal randomness Examples and application c03/2018 a0323243 a

When two players achieve a superclassical score at a nonlocal game, their outputs must contain intrinsic randomness. This fact has many useful implications for quantum cryptography. Recently it has been observed [C. Miller and Y. Shi, Quantum Inf. Computat. 17, 0595 (2017)] that such scores also imply the existence of local randomness—that is, randomness known to one player but not to the other. This has potential implications for cryptographic tasks between two cooperating but mistrustful players. In the current paper we bring this notion toward practical realization, by offering near-optimal bounds on local randomness for the CHSH game, and also proving the security of a cryptographic application of local randomness (single-bit certified deletion).

1 aFu, Honghao1 aMiller, Carl uhttps://arxiv.org/abs/1708.0433801356nas a2200181 4500008004100000245006000041210005900101260001500160490000700175520083200182100001801014700002401032700002301056700002201079700001501101700002101116856003701137 2018 eng d00aMachine learning assisted readout of trapped-ion qubits0 aMachine learning assisted readout of trappedion qubits c2018/05/010 v513 a

We reduce measurement errors in a quantum computer using machine learning techniques. We exploit a simple yet versatile neural network to classify multi-qubit quantum states, which is trained using experimental data. This flexible approach allows the incorporation of any number of features of the data with minimal modifications to the underlying network architecture. We experimentally illustrate this approach in the readout of trapped-ion qubits using additional spatial and temporal features in the data. Using this neural network classifier, we efficiently treat qubit readout crosstalk, resulting in a 30\% improvement in detection error over the conventional threshold method. Our approach does not depend on the specific details of the system and can be readily generalized to other quantum computing platforms.

1 aSeif, Alireza1 aLandsman, Kevin, A.1 aLinke, Norbert, M.1 aFiggatt, Caroline1 aMonroe, C.1 aHafezi, Mohammad uhttps://arxiv.org/abs/1804.0771801686nas a2200181 4500008004100000245006900041210006900110260001500179490000700194520113900201100002001340700002401360700002201384700001801406700002501424700001801449856003701467 2018 eng d00aOptimization of photon storage fidelity in ordered atomic arrays0 aOptimization of photon storage fidelity in ordered atomic arrays c2018/08/310 v203 a

A major application for atomic ensembles consists of a quantum memory for light, in which an optical state can be reversibly converted to a collective atomic excitation on demand. There exists a well-known fundamental bound on the storage error, when the ensemble is describable by a continuous medium governed by the Maxwell-Bloch equations. The validity of this model can break down, however, in systems such as dense, ordered atomic arrays, where strong interference in emission can give rise to phenomena such as subradiance and "selective" radiance. Here, we develop a general formalism that finds the maximum storage efficiency for a collection of atoms with discrete, known positions, and a given spatial mode in which an optical field is sent. As an example, we apply this technique to study a finite two-dimensional square array of atoms. We show that such a system enables a storage error that scales with atom number Na like ∼(logNa)2/N2a, and that, remarkably, an array of just 4×4 atoms in principle allows for an efficiency comparable to a disordered ensemble with optical depth of around 600.

1 aManzoni, M., T.1 aMoreno-Cardoner, M.1 aAsenjo-Garcia, A.1 aPorto, J., V.1 aGorshkov, Alexey, V.1 aChang, D., E. uhttps://arxiv.org/abs/1710.0631201943nas a2200169 4500008004100000245007600041210006900117520143500186100001601621700001801637700001801655700002101673700001201694700001501706700001501721856003701736 2018 eng d00aParallel Entangling Operations on a Universal Ion Trap Quantum Computer0 aParallel Entangling Operations on a Universal Ion Trap Quantum C3 a

The circuit model of a quantum computer consists of sequences of gate operations between quantum bits (qubits), drawn from a universal family of discrete operations. The ability to execute parallel entangling quantum gates offers clear efficiency gains in numerous quantum circuits as well as for entire algorithms such as Shor's factoring algorithm and quantum simulations. In cases such as full adders and multiple-control Toffoli gates, parallelism can provide an exponential improvement in overall execution time. More importantly, quantum gate parallelism is essential for the practical fault-tolerant error correction of qubits that suffer from idle errors. The implementation of parallel quantum gates is complicated by potential crosstalk, especially between qubits fully connected by a common-mode bus, such as in Coulomb-coupled trapped atomic ions or cavity-coupled superconducting transmons. Here, we present the first experimental results for parallel 2-qubit entangling gates in an array of fully-connected trapped ion qubits. We demonstrate an application of this capability by performing a 1-bit full addition operation on a quantum computer using a depth-4 quantum circuit. These results exploit the power of highly connected qubit systems through classical control techniques, and provide an advance toward speeding up quantum circuits and achieving fault tolerance with trapped ion quantum computers.

1 aFiggatt, C.1 aOstrander, A.1 aLinke, N., M.1 aLandsman, K., A.1 aZhu, D.1 aMaslov, D.1 aMonroe, C. uhttps://arxiv.org/abs/1810.1194802076nas a2200229 4500008004100000245007800041210006900119520136400188100002401552700001901576700002401595700001701619700002301636700002101659700001801680700002101698700001901719700002701738700001901765700002501784856003701809 2018 eng d00aPhoton propagation through dissipative Rydberg media at large input rates0 aPhoton propagation through dissipative Rydberg media at large in3 a

We study the dissipative propagation of quantized light in interacting Rydberg media under the conditions of electromagnetically induced transparency (EIT). Rydberg blockade physics in optically dense atomic media leads to strong dissipative interactions between single photons. The regime of high incoming photon flux constitutes a challenging many-body dissipative problem. We experimentally study in detail for the first time the pulse shapes and the second-order correlation function of the outgoing field and compare our data with simulations based on two novel theoretical approaches well-suited to treat this many-photon limit. At low incoming flux, we report good agreement between both theories and the experiment. For higher input flux, the intensity of the outgoing light is lower than that obtained from theoretical predictions. We explain this discrepancy using a simple phenomenological model taking into account pollutants, which are nearly-stationary Rydberg excitations coming from the reabsorption of scattered probe photons. At high incoming photon rates, the blockade physics results in unconventional shapes of measured correlation functions. 

1 aBienias, Przemyslaw1 aDouglas, James1 aParis-Mandoki, Asaf1 aTitum, Paraj1 aMirgorodskiy, Ivan1 aTresp, Christoph1 aZeuthen, Emil1 aGullans, Michael1 aManzoni, Marco1 aHofferberth, Sebastian1 aChang, Darrick1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1807.0758601386nas a2200193 4500008004100000245004800041210004700089260001500136520082300151100002300974700002300997700002101020700002101041700002401062700002501086700002701111700001701138856003701155 2018 eng d00aPhoton Subtraction by Many-Body Decoherence0 aPhoton Subtraction by ManyBody Decoherence c2018/03/133 a

We present an experimental and theoretical investigation of the scattering-induced decoherence of multiple photons stored in a strongly interacting atomic ensemble. We derive an exact solution to this many-body problem, allowing for a rigorous understanding of the underlying dissipative quantum dynamics. Combined with our experiments, this analysis demonstrates a correlated coherence-protection process, in which the induced decoherence of one photon can preserve the spatial coherence of all others. We discuss how this effect can be used to manipulate light at the quantum level, providing a robust mechanism for single-photon subtraction, and experimentally demonstrate this capability.

1 aMurray, Callum, R.1 aMirgorodskiy, Ivan1 aTresp, Christoph1 aBraun, Christoph1 aParis-Mandoki, Asaf1 aGorshkov, Alexey, V.1 aHofferberth, Sebastian1 aPohl, Thomas uhttps://arxiv.org/abs/1710.1004702448nas a2200133 4500008004100000245006700041210006500108520202500173100001902198700002202217700002302239700001502262856003702277 2018 eng d00aQuantum-secure message authentication via blind-unforgeability0 aQuantumsecure message authentication via blindunforgeability3 a

Formulating and designing unforgeable authentication of classical messages in the presence of quantum adversaries has been a challenge, as the familiar classical notions of unforgeability do not directly translate into meaningful notions in the quantum setting. A particular difficulty is how to fairly capture the notion of "predicting an unqueried value" when the adversary can query in quantum superposition. In this work, we uncover serious shortcomings in existing approaches, and propose a new definition. We then support its viability by a number of constructions and characterizations. Specifically, we demonstrate a function which is secure according to the existing definition by Boneh and Zhandry, but is clearly vulnerable to a quantum forgery attack, whereby a query supported only on inputs that start with 0 divulges the value of the function on an input that starts with 1. We then propose a new definition, which we call "blind-unforgeability" (or BU.) This notion matches "intuitive unpredictability" in all examples studied thus far. It defines a function to be predictable if there exists an adversary which can use "partially blinded" oracle access to predict values in the blinded region. Our definition (BU) coincides with standard unpredictability (EUF-CMA) in the classical-query setting. We show that quantum-secure pseudorandom functions are BU-secure MACs. In addition, we show that BU satisfies a composition property (Hash-and-MAC) using "Bernoulli-preserving" hash functions, a new notion which may be of independent interest. Finally, we show that BU is amenable to security reductions by giving a precise bound on the extent to which quantum algorithms can deviate from their usual behavior due to the blinding in the BU security experiment. 

1 aAlagic, Gorjan1 aMajenz, Christian1 aRussell, Alexander1 aSong, Fang uhttps://arxiv.org/abs/1803.0376101532nas a2200193 4500008004100000245009300041210006900134260001500203300001100218490000800229520089100237100002101128700002401149700002201173700002301195700002401218700002301242856007301265 2018 eng d00aRobust two-qubit gates in a linear ion crystal using a frequency-modulated driving force0 aRobust twoqubit gates in a linear ion crystal using a frequencym c2018/01/09 a0205010 v1203 a

In an ion trap quantum computer, collective motional modes are used to entangle two or more qubits in order to execute multi-qubit logical gates. Any residual entanglement between the internal and motional states of the ions will result in decoherence errors, especially when there are many spectator ions in the crystal. We propose using a frequency-modulated (FM) driving force to minimize such errors and implement it experimentally. In simulation, we obtained an optimized FM gate that can suppress decoherence to less than 10−4 and is robust against a frequency drift of more than ±1 kHz. The two-qubit gate was tested in a five-qubit trapped ion crystal, with 98.3(4)% fidelity for a Mølmer-Sørensen entangling gate and 98.6(7)% for a controlled-not (CNOT) gate. We also show an optimized FM two-qubit gate for 17 ions, proving the scalability of our method.

1 aLeung, Pak, Hong1 aLandsman, Kevin, A.1 aFiggatt, Caroline1 aLinke, Norbert, M.1 aMonroe, Christopher1 aBrown, Kenneth, R. uhttps://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.02050101174nas a2200109 4500008004100000245007300041210006900114520080600183100001900989700001901008856003701027 2018 eng d00aA semiclassical theory of phase-space dynamics of interacting bosons0 asemiclassical theory of phasespace dynamics of interacting boson3 a

We study the phase-space representation of dynamics of bosons in the semiclassical regime where the occupation number of the modes is large. To this end, we employ the van Vleck-Gutzwiller propagator to obtain an approximation for the Green's function of the Wigner distribution. The semiclassical analysis incorporates interference of classical paths and reduces to the truncated Wigner approximation (TWA) when the interference is ignored. Furthermore, we identify the Ehrenfest time after which the TWA fails. As a case study, we consider a single-mode quantum nonlinear oscillator, which displays collapse and revival of observables. We analytically show that the interference of classical paths leads to revivals, an effect that is not reproduced by the TWA or a perturbative analysis.

1 aMathew, Ranchu1 aTiesinga, Eite uhttps://arxiv.org/abs/1803.0512201648nas a2200169 4500008004100000245006100041210006100102300001400163490000900177520116300186100002301349700001901372700001801391700001901409700001301428856003701441 2018 eng d00aToward the first quantum simulation with quantum speedup0 aToward the first quantum simulation with quantum speedup a9456-94610 v115 3 a

With quantum computers of significant size now on the horizon, we should understand how to best exploit their initially limited abilities. To this end, we aim to identify a practical problem that is beyond the reach of current classical computers, but that requires the fewest resources for a quantum computer. We consider quantum simulation of spin systems, which could be applied to understand condensed matter phenomena. We synthesize explicit circuits for three leading quantum simulation algorithms, using diverse techniques to tighten error bounds and optimize circuit implementations. Quantum signal processing appears to be preferred among algorithms with rigorous performance guarantees, whereas higher-order product formulas prevail if empirical error estimates suffice. Our circuits are orders of magnitude smaller than those for the simplest classically infeasible instances of factoring and quantum chemistry, bringing practical quantum computation closer to reality.

1 aChilds, Andrew, M.1 aMaslov, Dmitri1 aNam, Yunseong1 aRoss, Neil, J.1 aSu, Yuan uhttps://arxiv.org/abs/1711.1098001463nas a2200121 4500008004100000245007300041210006900114520107000183100001701253700001601270700001801286856003701304 2018 eng d00aTwo-Dimensional Dilaton Gravity Theory and Lattice Schwarzian Theory0 aTwoDimensional Dilaton Gravity Theory and Lattice Schwarzian The3 a
We report a holographic study of a two-dimensional dilaton gravity theory with the Dirichlet boundary condition for the cases of non-vanishing and vanishing cosmological constants. Our result shows that the boundary theory of the two-dimensional dilaton gravity theory with the Dirichlet boundary condition for the case of non-vanishing cosmological constants is the Schwarzian term coupled to a dilaton field, while for the case of vanishing cosmological constant, a theory does not have a kinetic term. We also include the higher derivative term R2, where R is the scalar curvature that is coupled to a dilaton field. We find that the form of the boundary theory is not modified perturbatively. Finally, we show that a lattice holographic picture is realized up to the second-order perturbation of boundary cut-off ε2 under a constant boundary dilaton field and the non-vanishing cosmological constant by identifying the lattice spacing a of a lattice Schwarzian theory with the boundary cut-off ε of the two-dimensional dilaton gravity theory. 
1 aChu, Su-Kuan1 aMa, Chen-Te1 aWu, Chih-Hung uhttps://arxiv.org/abs/1802.0459901724nas a2200133 4500008004100000245003500041210003500076490001000111520132700121100001901448700002501467700002201492856007601514 2018 eng d00aUnforgeable Quantum Encryption0 aUnforgeable Quantum Encryption0 v108223 a

We study the problem of encrypting and authenticating quantum data in the presence of adversaries making adaptive chosen plaintext and chosen ciphertext queries. Classically, security games use string copying and comparison to detect adversarial cheating in such scenarios. Quantumly, this approach would violate no-cloning. We develop new techniques to overcome this problem: we use entanglement to detect cheating, and rely on recent results for characterizing quantum encryption schemes. We give definitions for (i) ciphertext unforgeability, (ii) indistinguishability under adaptive chosen-ciphertext attack, and (iii) authenticated encryption. The restriction of each definition to the classical setting is at least as strong as the corresponding classical notion: (i) implies   INT-CTXT , (ii) implies   IND-CCA2 , and (iii) implies   AE . All of our new notions also imply   QIND-CPA  privacy. Combining one-time authentication and classical pseudorandomness, we construct symmetric-key quantum encryption schemes for each of these new security notions, and provide several separation examples. Along the way, we also give a new definition of one-time quantum authentication which, unlike all previous approaches, authenticates ciphertexts rather than plaintexts.

1 aAlagic, Gorjan1 aGagliardoni, Tommaso1 aMajenz, Christian uhttps://www.quics.umd.edu/publications/unforgeable-quantum-encryption-001858nas a2200169 4500008004100000245004400041210004400085520137000129100002401499700002201523700002101545700002301566700001801589700002001607700002401627856003701651 2018 eng d00aVerified Quantum Information Scrambling0 aVerified Quantum Information Scrambling3 a

Quantum scrambling is the dispersal of local information into many-body quantum entanglements and correlations distributed throughout the entire system. This concept underlies the dynamics of thermalization in closed quantum systems, and more recently has emerged as a powerful tool for characterizing chaos in black holes. However, the direct experimental measurement of quantum scrambling is difficult, owing to the exponential complexity of ergodic many-body entangled states. One way to characterize quantum scrambling is to measure an out-of-time-ordered correlation function (OTOC); however, since scrambling leads to their decay, OTOCs do not generally discriminate between quantum scrambling and ordinary decoherence. Here, we implement a quantum circuit that provides a positive test for the scrambling features of a given unitary process. This approach conditionally teleports a quantum state through the circuit, providing an unambiguous litmus test for scrambling while projecting potential circuit errors into an ancillary observable. We engineer quantum scrambling processes through a tunable 3-qubit unitary operation as part of a 7-qubit circuit on an ion trap quantum computer. Measured teleportation fidelities are typically ∼80%, and enable us to experimentally bound the scrambling-induced decay of the corresponding OTOC measurement.

1 aLandsman, Kevin, A.1 aFiggatt, Caroline1 aSchuster, Thomas1 aLinke, Norbert, M.1 aYoshida, Beni1 aYao, Norman, Y.1 aMonroe, Christopher uhttps://arxiv.org/abs/1806.0280701713nas a2200133 4500008004100000245007300041210006900114260001500183300001100198490000700209520120600216100001901422856013801441 2017 eng d00aBasic circuit compilation techniques for an ion-trap quantum machine0 aBasic circuit compilation techniques for an iontrap quantum mach c2016/02/20 a0230350 v193 a

We study the problem of compilation of quantum algorithms into optimized physical-level circuits executable in a quantum information processing (QIP) experiment based on trapped atomic ions. We report a complete strategy: starting with an algorithm in the form of a quantum computer program, we compile it into a high-level logical circuit that goes through multiple stages of decomposition into progressively lower-level circuits until we reach the physical execution-level specification. We skip the fault-tolerance layer, as it is not necessary in this work. The different stages are structured so as to best assist with the overall optimization while taking into account numerous optimization criteria, including minimizing the number of expensive two-qubit gates, minimizing the number of less expensive single-qubit gates, optimizing the runtime, minimizing the overall circuit error, and optimizing classical control sequences. Our approach allows a trade-off between circuit runtime and quantum error, as well as to accommodate future changes in the optimization criteria that may likely arise as a result of the anticipated improvements in the physical-level control of the experiment.

1 aMaslov, Dmitri uhttp://iopscience.iop.org/article/10.1088/1367-2630/aa5e47/meta;jsessionid=55CC235A0B106081E825099310586F07.c3.iopscience.cld.iop.org02065nas a2200169 4500008004100000245007000041210006900111260001500180520154900195100001601744700001901760700002101779700001801800700001601818700002401834856003701858 2017 eng d00aComplete 3-Qubit Grover Search on a Programmable Quantum Computer0 aComplete 3Qubit Grover Search on a Programmable Quantum Computer c2017/03/303 a

Searching large databases is an important problem with broad applications. The Grover search algorithm provides a powerful method for quantum computers to perform searches with a quadratic speedup in the number of required database queries over classical computers. It is an optimal search algorithm for a quantum computer, and has further applications as a subroutine for other quantum algorithms. Searches with two qubits have been demonstrated on a variety of platforms and proposed for others, but larger search spaces have only been demonstrated on a non-scalable NMR system. Here, we report results for a complete three-qubit Grover search algorithm using the scalable quantum computing technology of trapped atomic ions, with better-than-classical performance. The algorithm is performed for all 8 possible single-result oracles and all 28 possible two-result oracles. Two methods of state marking are used for the oracles: a phase-flip method employed by other experimental demonstrations, and a Boolean method requiring an ancilla qubit that is directly equivalent to the state-marking scheme required to perform a classical search. All quantum solutions are shown to outperform their classical counterparts. We also report the first implementation of a Toffoli-4 gate, which is used along with Toffoli-3 gates to construct the algorithms; these gates have process fidelities of 70.5% and 89.6%, respectively.

1 aFiggatt, C.1 aMaslov, Dmitri1 aLandsman, K., A.1 aLinke, N., M.1 aDebnath, S.1 aMonroe, Christopher uhttps://arxiv.org/abs/1703.1053501698nas a2200169 4500008004100000245006000041210006000101260001500161300001100176490000800187520120500195100001801400700002101418700002701439700002501466856003701491 2017 eng d00aCorrelated Photon Dynamics in Dissipative Rydberg Media0 aCorrelated Photon Dynamics in Dissipative Rydberg Media c2017/07/26 a0436020 v1193 a

Rydberg blockade physics in optically dense atomic media under the conditions of electromagnetically induced transparency (EIT) leads to strong dissipative interactions between single photons. We introduce a new approach to analyzing this challenging many-body problem in the limit of large optical depth per blockade radius. In our approach, we separate the single-polariton EIT physics from Rydberg-Rydberg interactions in a serialized manner while using a hard-sphere model for the latter, thus capturing the dualistic particle-wave nature of light as it manifests itself in dissipative Rydberg-EIT media. Using this approach, we analyze the saturation behavior of the transmission through one-dimensional Rydberg-EIT media in the regime of non-perturbative dissipative interactions relevant to current experiments. Our model is in good agreement with experimental data. We also analyze a scheme for generating regular trains of single photons from continuous-wave input and derive its scaling behavior in the presence of imperfect single-photon EIT.

1 aZeuthen, Emil1 aGullans, Michael1 aMaghrebi, Mohammad, F.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1608.0606801586nas a2200193 4500008004100000245007900041210006900120260001400189490000700203520099200210100002401202700002201226700002201248700001901270700002001289700002701309700001901336856003701355 2017 eng d00aDevelopment of a new UHV/XHV pressure standard (cold atom vacuum standard)0 aDevelopment of a new UHVXHV pressure standard cold atom vacuum s c2017/11/30 v543 a

The National Institute of Standards and Technology has recently begun a program to develop a primary pressure standard that is based on ultra-cold atoms, covering a pressure range of 1 x 10-6 to 1 x 10-10 Pa and possibly lower. These pressures correspond to the entire ultra-high vacuum range and extend into the extreme-high vacuum. This cold-atom vacuum standard (CAVS) is both a primary standard and absolute sensor of vacuum. The CAVS is based on the loss of cold, sensor atoms (such as the alkali-metal lithium) from a magnetic trap due to collisions with the background gas (primarily H2) in the vacuum. The pressure is determined from a thermally-averaged collision cross section, which is a fundamental atomic property, and the measured loss rate. The CAVS is primary because it will use collision cross sections determined from ab initio calculations for the Li + H2 system. Primary traceability is transferred to other systems of interest using sensitivity coefficients.

1 aScherschligt, Julia1 aFedchak, James, A1 aBarker, Daniel, S1 aEckel, Stephen1 aKlimov, Nikolai1 aMakrides, Constantinos1 aTiesinga, Eite uhttps://arxiv.org/abs/1801.1012001103nas a2200109 4500008004100000245008300041210006900124260001500193520073100208100001700939856003700956 2017 eng d00aAn Elementary Proof of Private Random Number Generation from Bell Inequalities0 aElementary Proof of Private Random Number Generation from Bell I c2017/07/203 a

The field of device-independent quantum cryptography has seen enormous success in the past several years, including security proofs for key distribution and random number generation that account for arbitrary imperfections in the devices used. Full security proofs in the field so far are long and technically deep. In this paper we show that the concept of the mirror adversary can be used to simplify device-independent proofs. We give a short proof that any bipartite Bell violation can be used to generate private random numbers. The proof is based on elementary techniques and is self-contained.

1 aMiller, Carl uhttps://arxiv.org/abs/1707.0659702145nas a2200205 4500008004100000245005800041210005700099260001500156300001100171490000700182520152100189100002301710700002101733700002201754700002101776700002501797700002101822700002701843856006901870 2017 eng d00aEmergent equilibrium in many-body optical bistability0 aEmergent equilibrium in manybody optical bistability c2017/04/17 a0438260 v953 a

Many-body systems constructed of quantum-optical building blocks can now be realized in experimental platforms ranging from exciton-polariton fluids to ultracold gases of Rydberg atoms, establishing a fascinating interface between traditional many-body physics and the driven-dissipative, non-equilibrium setting of cavity-QED. At this interface, the standard techniques and intuitions of both fields are called into question, obscuring issues as fundamental as the role of fluctuations, dimensionality, and symmetry on the nature of collective behavior and phase transitions. Here, we study the driven-dissipative Bose-Hubbard model, a minimal description of numerous atomic, optical, and solid-state systems in which particle loss is countered by coherent driving. Despite being a lattice version of optical bistability---a foundational and patently non-equilibrium model of cavity-QED---the steady state possesses an emergent equilibrium description in terms of a classical Ising model. We establish this picture by identifying a limit in which the quantum dynamics is asymptotically equivalent to non-equilibrium Langevin equations, which support a phase transition described by model A of the Hohenberg-Halperin classification. Numerical simulations of the Langevin equations corroborate this picture, producing results consistent with the behavior of a finite-temperature Ising model.

1 aFoss-Feig, Michael1 aNiroula, Pradeep1 aYoung, Jeremy, T.1 aHafezi, Mohammad1 aGorshkov, Alexey, V.1 aWilson, Ryan, M.1 aMaghrebi, Mohammad, F. uhttps://journals.aps.org/pra/abstract/10.1103/PhysRevA.95.04382601709nas a2200229 4500008004100000245006700041210006700108250000700175260001500182300001400197490000800211520106700219100001601286700001901302700002201321700001601343700001601359700002101375700001501396700002401411856004401435 2017 eng d00aExperimental Comparison of Two Quantum Computing Architectures0 aExperimental Comparison of Two Quantum Computing Architectures a13 c2017/03/21 a3305-33100 v1143 a

We run a selection of algorithms on two state-of-the-art 5-qubit quantum computers that are based on different technology platforms. One is a publicly accessible superconducting transmon device [1] with limited connectivity, and the other is a fully connected trapped-ion system [2]. Even though the two systems have different native quantum interactions, both can be programmed in a way that is blind to the underlying hardware, thus allowing the first comparison of identical quantum algorithms between different physical systems. We show that quantum algorithms and circuits that employ more connectivity clearly benefit from a better connected system of qubits. While the quantum systems here are not yet large enough to eclipse classical computers, this experiment exposes critical factors of scaling quantum computers, such as qubit connectivity and gate expressivity. In addition, the results suggest that co-designing particular quantum applications with the hardware itself will be paramount in successfully using quantum computers in the future.

1 aLinke, N.M.1 aMaslov, Dmitri1 aRoetteler, Martin1 aDebnath, S.1 aFiggatt, C.1 aLandsman, K., A.1 aWright, K.1 aMonroe, Christopher uhttp://www.pnas.org/content/114/13/330501121nas a2200169 4500008004100000245007000041210006900111260001500180300001100195490000800206520058700214100002200801700001900823700001900842700001700861856007300878 2017 eng d00aExperimental demonstration of cheap and accurate phase estimation0 aExperimental demonstration of cheap and accurate phase estimatio c2017/05/12 a1905020 v1183 a

We demonstrate experimental implementation of robust phase estimation (RPE) to learn the phases of X and Y rotations on a trapped Yb+ ion qubit. We estimate these phases with uncertainties less than 4 · 10−4 radians using as few as 176 total experimental samples per phase, and our estimates exhibit Heisenberg scaling. Unlike standard phase estimation protocols, RPE neither assumes perfect state preparation and measurement, nor requires access to ancillae. We cross-validate the results of RPE with the more resource-intensive protocol of gate set tomography.

1 aRudinger, Kenneth1 aKimmel, Shelby1 aLobser, Daniel1 aMaunz, Peter uhttps://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.19050201575nas a2200217 4500008004100000245010100041210006900142260001500211520089600226100002101122700001901143700001801162700001501180700002401195700001901219700001601238700002501254700001801279700002201297856003801319 2017 eng d00aExperimentally Generated Random Numbers Certified by the Impossibility of Superluminal Signaling0 aExperimentally Generated Random Numbers Certified by the Impossi c2017/02/163 a

Random numbers are an important resource for applications such as numerical simulation and secure communication. However, it is difficult to certify whether a physical random number generator is truly unpredictable. Here, we exploit the phenomenon of quantum nonlocality in a loophole-free photonic Bell test experiment for the generation of randomness that cannot be predicted within any physical theory that allows one to make independent measurement choices and prohibits superluminal signaling. To certify and quantify the randomness, we describe a new protocol that performs well in an experimental regime characterized by low violation of Bell inequalities. Applying an extractor function to our data, we obtained 256 new random bits, uniform to within 0.001.

1 aBierhorst, Peter1 aKnill, Emanuel1 aGlancy, Scott1 aMink, Alan1 aJordan, Stephen, P.1 aRommal, Andrea1 aLiu, Yi-Kai1 aChristensen, Bradley1 aNam, Sae, Woo1 aShalm, Lynden, K. uhttps://arxiv.org/abs/1702.05178#27528nas a2200181 45000080041000002450087000412100069001282600015001973000011002124900008002235202696300231100002227194700001927216700002627235700002327261700002527284856003727309 2017 eng d00aFast State Transfer and Entanglement Renormalization Using Long-Range Interactions0 aFast State Transfer and Entanglement Renormalization Using LongR c2017/10/25 a1705030 v1193 a

In short-range interacting systems, the speed at which entanglement can be established between two separated points is limited by a constant Lieb-Robinson velocity. Long-range interacting systems are capable of faster entanglement generation, but the degree of the speed-up possible is an open question. In this paper, we present a protocol capable of transferring a quantum state across a distance L in d dimensions using long-range interactions with strength bounded by 1/rα. If α<d, the state transfer time is asymptotically independent of L; if α=d, the time is logarithmic in distance L; if d<α<d+1, transfer occurs in time proportional to Lαd; and if αd+1, it occurs in time proportional to L. We then use this protocol to upper bound the time required to create a state specified by a MERA (multiscale entanglement renormalization ansatz) tensor network, and show that, if the linear size of the MERA state is L, then it can be created in time that scales with L identically to state transfer up to multiplicative logarithmic corrections.

1 aEldredge, Zachary1 aGong, Zhe-Xuan1 aMoosavian, Ali, Hamed1 aFoss-Feig, Michael1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1612.0244201674nas a2200181 4500008004100000245007500041210006900116260001500185300001100200490000700211520113600218100001501354700001101369700001901380700001801399700001901417856005601436 2017 eng d00aInput-output theory for spin-photon coupling in Si double quantum dots0 aInputoutput theory for spinphoton coupling in Si double quantum  c2017/12/22 a2354340 v963 a

The interaction of qubits via microwave frequency photons enables long-distance qubit-qubit coupling and facilitates the realization of a large-scale quantum processor. However, qubits based on electron spins in semiconductor quantum dots have proven challenging to couple to microwave photons. In this theoretical work we show that a sizable coupling for a single electron spin is possible via spin-charge hybridization using a magnetic field gradient in a silicon double quantum dot. Based on parameters already shown in recent experiments, we predict optimal working points to achieve a coherent spin-photon coupling, an essential ingredient for the generation of long-range entanglement. Furthermore, we employ input-output theory to identify observable signatures of spin-photon coupling in the cavity output field, which may provide guidance to the experimental search for strong coupling in such spin-photon systems and opens the way to cavity-based readout of the spin qubit.

1 aBenito, M.1 aMi, X.1 aTaylor, J., M.1 aPetta, J., R.1 aBurkard, Guido uhttps://link.aps.org/doi/10.1103/PhysRevB.96.23543401208nas a2200169 4500008004100000245005700041210005600098260001500154300001100169490000700180520068400187100002600871700002700897700002500924700002000949856006900969 2017 eng d00aMulticritical behavior in dissipative {I}sing models0 aMulticritical behavior in dissipative I sing models c2017/04/26 a0421330 v953 a

We analyze theoretically the many-body dynamics of a dissipative Ising model in a transverse field using a variational approach. We find that the steady state phase diagram is substantially modified compared to its equilibrium counterpart, including the appearance of a multicritical point belonging to a different universality class. Building on our variational analysis, we establish a field-theoretical treatment corresponding to a dissipative variant of a Ginzburg-Landau theory, which allows us to compute the upper critical dimension of the system. Finally, we present a possible experimental realization of the dissipative Ising model using ultracold Rydberg gases.

1 aOverbeck, Vincent, R.1 aMaghrebi, Mohammad, F.1 aGorshkov, Alexey, V.1 aWeimer, Hendrik uhttps://journals.aps.org/pra/abstract/10.1103/PhysRevA.95.04213301952nas a2200229 4500008004100000245009200041210006900133260001500202300001200217490000800229520128300237100001401520700001501534700001701549700002001566700001501586700001501601700002501616700001801641700001501659856004801674 2017 eng d00aObservation of a Many-Body Dynamical Phase Transition with a 53-Qubit Quantum Simulator0 aObservation of a ManyBody Dynamical Phase Transition with a 53Qu c2017/11/29 a601-6040 v5513 a

A quantum simulator is a restricted class of quantum computer that controls the interactions between quantum bits in a way that can be mapped to certain difficult quantum many-body problems. As more control is exerted over larger numbers of qubits, the simulator can tackle a wider range of problems, with the ultimate limit being a universal quantum computer that can solve general classes of hard problems. We use a quantum simulator composed of up to 53 qubits to study a non-equilibrium phase transition in the transverse field Ising model of magnetism, in a regime where conventional statistical mechanics does not apply. The qubits are represented by trapped ion spins that can be prepared in a variety of initial pure states. We apply a global long-range Ising interaction with controllable strength and range, and measure each individual qubit with near 99% efficiency. This allows the single-shot measurement of arbitrary many-body correlations for the direct probing of the dynamical phase transition and the uncovering of computationally intractable features that rely on the long-range interactions and high connectivity between the qubits.

1 aZhang, J.1 aPagano, G.1 aHess, P., W.1 aKyprianidis, A.1 aBecker, P.1 aKaplan, H.1 aGorshkov, Alexey, V.1 aGong, Z., -X.1 aMonroe, C. uhttps://www.nature.com/articles/nature2465401351nas a2200157 4500008004100000245007200041210006900113260001500182300001100197490000700208520084900215100002401064700002301088700002701111856005501138 2017 eng d00aPartial breakdown of quantum thermalization in a Hubbard-like model0 aPartial breakdown of quantum thermalization in a Hubbardlike mod c2017/02/17 a0542040 v953 a

We study the possible breakdown of quantum thermalization in a model of itinerant electrons on a one-dimensional chain without disorder, with both spin and charge degrees of freedom. The eigenstates of this model exhibit peculiar properties in the entanglement entropy, the apparent scaling of which is modified from a “volume law” to an “area law” after performing a partial, site-wise measurement on the system. These properties and others suggest that this model realizes a new, nonthermal phase of matter, known as a quantum disentangled liquid (QDL). The putative existence of this phase has striking implications for the foundations of quantum statistical mechanics.

1 aGarrison, James, R.1 aMishmash, Ryan, V.1 aFisher, Matthew, P. A. uhttp://link.aps.org/doi/10.1103/PhysRevB.95.05420417147nas a2200181 45000080041000002450100000412100069001412600015002103000011002254900007002365201657700243100001316820700002216833700002716855700001916882700002716901856003716928 2017 eng d00aPendular trapping conditions for ultracold polar molecules enforced by external electric fields0 aPendular trapping conditions for ultracold polar molecules enfor c2017/06/26 a0634220 v953 a

We theoretically investigate trapping conditions for ultracold polar molecules in optical lattices, when external magnetic and electric fields are simultaneously applied. Our results are based on an accurate electronic-structure calculation of the polar 23Na40K polar molecule in its absolute ground state combined with a calculation of its rovibrational-hyperfine motion. We find that an electric field strength of 5.26(15) kV/cm and an angle of 54.7 between this field and the polarization of the optical laser lead to a trapping design for 23Na40K molecules where decoherences due laser-intensity fluctuations and fluctuations in the direction of its polarization are kept to a minimum. One standard deviation systematic and statistical uncertainties are given in parenthesis. Under such conditions pairs of hyperfine-rotational states of v=0 molecules, used to induce tunable dipole-dipole interactions between them, experience ultrastable, matching trapping forces.

1 aLi, Ming1 aPetrov, Alexander1 aMakrides, Constantinos1 aTiesinga, Eite1 aKotochigova, Svetlanta uhttps://arxiv.org/abs/1703.0383901572nas a2200145 4500008004100000245008400041210006900125260001500194300001100209490000700220520112400227100001901351700001901370856003701389 2017 eng d00aPhase-space mixing in dynamically unstable, integrable few-mode quantum systems0 aPhasespace mixing in dynamically unstable integrable fewmode qua c2017/07/05 a0136040 v963 a

Quenches in isolated quantum systems are currently a subject of intense study. Here, we consider quantum few-mode systems that are integrable in their classical mean-field limit and become dynamically unstable after a quench of a system parameter. Specifically, we study a Bose-Einstein condensate (BEC) in a double-well potential and an antiferromagnetic spinor BEC constrained to a single spatial mode. We study the time dynamics after the quench within the truncated Wigner approximation (TWA) and find that system relaxes to a steady state due to phase-space mixing. Using the action-angle formalism and a pendulum as an illustration, we derive general analytical expressions for the time evolution of expectation values of observables and their long-time limits. We find that the deviation of the long-time expectation value from its classical value scales as 1/O(ln N), where N is the number of atoms in the condensate. Furthermore, the relaxation of an observable to its steady state value is a damped oscillation and the damping is Gaussian in time. We confirm our results with numerical TWA simulations.

1 aMathew, Ranchu1 aTiesinga, Eite uhttps://arxiv.org/abs/1705.0170201828nas a2200121 4500008004100000245004800041210004700089490001000136520143200146100001901578700002201597856008701619 2017 eng d00aQuantum Non-malleability and Authentication0 aQuantum Nonmalleability and Authentication0 v104023 a

In encryption, non-malleability is a highly desirable property: it ensures that adversaries cannot manipulate the plaintext by acting on the ciphertext. In [6], Ambainis et al. gave a definition of non-malleability for the encryption of quantum data. In this work, we show that this definition is too weak, as it allows adversaries to “inject” plaintexts of their choice into the ciphertext. We give a new definition of quantum non-malleability which resolves this problem. Our definition is expressed in terms of entropic quantities, considers stronger adversaries, and does not assume secrecy. Rather, we prove that quantum non-malleability implies secrecy; this is in stark contrast to the classical setting, where the two properties are completely independent. For unitary schemes, our notion of non-malleability is equivalent to encryption with a two-design (and hence also to the definition of [6]).

Our techniques also yield new results regarding the closely-related task of quantum authentication. We show that “total authentication” (a notion recently proposed by Garg et al. [18]) can be satisfied with two-designs, a significant improvement over the eight-design construction of [18]. We also show that, under a mild adaptation of the rejection procedure, both total authentication and our notion of non-malleability yield quantum authentication as defined by Dupuis et al. [16].

1 aAlagic, Gorjan1 aMajenz, Christian uhttps://www.quics.umd.edu/publications/quantum-non-malleability-and-authentication01598nas a2200241 4500008004100000245005800041210005800099260001500157300001100172490000800183520093100191100001301122700001401135700001801149700001601167700001801183700001801201700001301219700001601232700001401248700002201262856007201284 2017 eng d00aQuantum state tomography via reduced density matrices0 aQuantum state tomography via reduced density matrices c2017/01/09 a0204010 v1183 a

Quantum state tomography via local measurements is an efficient tool for characterizing quantum states. However it requires that the original global state be uniquely determined (UD) by its local reduced density matrices (RDMs). In this work we demonstrate for the first time a class of states that are UD by their RDMs under the assumption that the global state is pure, but fail to be UD in the absence of that assumption. This discovery allows us to classify quantum states according to their UD properties, with the requirement that each class be treated distinctly in the practice of simplifying quantum state tomography. Additionally we experimentally test the feasibility and stability of performing quantum state tomography via the measurement of local RDMs for each class. These theoretical and experimental results advance the project of performing efficient and accurate quantum state tomography in practice.

1 aXin, Tao1 aLu, Dawei1 aKlassen, Joel1 aYu, Nengkun1 aJi, Zhengfeng1 aChen, Jianxin1 aMa, Xian1 aLong, Guilu1 aZeng, Bei1 aLaflamme, Raymond uhttp://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.02040101545nas a2200145 4500008004100000245006100041210006100102260001500163300001400178490000700192520113000199100001701329700001601346856003701362 2017 eng d00aRandomness in nonlocal games between mistrustful players0 aRandomness in nonlocal games between mistrustful players c2017/06/15 a0595-06100 v173 a

If two quantum players at a nonlocal game G achieve a superclassical score, then their measurement outcomes must be at least partially random from the perspective of any third player. This is the basis for device-independent quantum cryptography. In this paper we address a related question: does a superclassical score at G guarantee that one player has created randomness from the perspective of the other player? We show that for complete-support games, the answer is yes: even if the second player is given the first player's input at the conclusion of the game, he cannot perfectly recover her output. Thus some amount of local randomness (i.e., randomness possessed by only one player) is always obtained when randomness is certified from nonlocal games with quantum strategies. This is in contrast to non-signaling game strategies, which may produce global randomness without any local randomness. We discuss potential implications for cryptographic protocols between mistrustful parties.

1 aMiller, Carl1 aShi, Yaoyun uhttps://arxiv.org/abs/1706.0498401315nas a2200145 4500008004100000245004100041210004100082260001500123300001100138490000600149520091300155100001601068700001701084856006801101 2017 eng d00aRigidity of the magic pentagram game0 aRigidity of the magic pentagram game c2017/11/02 a0150020 v33 a

A game is rigid if a near-optimal score guarantees, under the sole assumption of the validity of quantum mechanics, that the players are using an approximately unique quantum strategy. Rigidity has a vital role in quantum cryptography as it permits a strictly classical user to trust behavior in the quantum realm. This property can be traced back as far as 1998 (Mayers and Yao) and has been proved for multiple classes of games. In this paper we prove ridigity for the magic pentagram game, a simple binary constraint satisfaction game involving two players, five clauses and ten variables. We show that all near-optimal strategies for the pentagram game are approximately equivalent to a unique strategy involving real Pauli measurements on three maximally-entangled qubit pairs.

1 aKalev, Amir1 aMiller, Carl uhttp://iopscience.iop.org/article/10.1088/2058-9565/aa931d/meta02412nas a2200145 4500008004100000245006200041210006100103260001500164300001400179520194800193100002102141700002402162700002202186856005802208 2017 eng d00aSequential measurements, disturbance and property testing0 aSequential measurements disturbance and property testing c2017/01/01 a1598-16113 a

We describe two procedures which, given access to one copy of a quantum state and a sequence of two-outcome measurements, can distinguish between the case that at least one of the measurements accepts the state with high probability, and the case that all of the measurements have low probability of acceptance. The measurements cannot simply be tried in sequence, because early measurements may disturb the state being tested. One procedure is based on a variant of Marriott-Watrous amplification. The other procedure is based on the use of a test for this disturbance, which is applied with low probability. We find a number of applications. First, quantum query complexity separations in the property testing model for testing isomorphism of functions under group actions. We give quantum algorithms for testing isomorphism, linear isomorphism and affine isomorphism of boolean functions which use exponentially fewer queries than is possible classically, and a quantum algorithm for testing graph isomorphism which uses polynomially fewer queries than the best algorithm known. Second, testing properties of quantum states and operations. We show that any finite property of quantum states can be tested using a number of copies of the state which is logarithmic in the size of the property, and give a test for genuine multipartite entanglement of states of n qubits that uses O(n) copies of the state. Third, correcting an error in a result of Aaronson on de-Merlinizing quantum protocols. This result claimed that, in any one-way quantum communication protocol where two parties are assisted by an all-powerful but untrusted third party, the third party can be removed with only a modest increase in the communication cost. We give a corrected proof of a key technical lemma required for Aaronson's result.

1 aHarrow, Aram, W.1 aLin, Cedric, Yen-Yu1 aMontanaro, Ashley uhttp://epubs.siam.org/doi/10.1137/1.9781611974782.10501977nas a2200121 4500008004100000245009300041210006900134260001500203520155900218100001901777700002201796856003701818 2017 eng d00aShorter stabilizer circuits via Bruhat decomposition and quantum circuit transformations0 aShorter stabilizer circuits via Bruhat decomposition and quantum c2017/05/253 a

In this paper we improve the layered implementation of arbitrary stabilizer circuits introduced by Aaronson and Gottesman in Phys. Rev. A 70(052328), 2004: to implement a general stabilizer circuit, we reduce their 11-stage computation -HC-P-C-P-C-H-P-C-P-C- over the gate set consisting of Hadamard, Controlled-NOT, and Phase gates, into a 7-stage computation of the form -C-CZ-P-H-P-CZ-C-. We show arguments in support of using -CZ- stages over the -C- stages: not only the use of -CZ- stages allows a shorter layered expression, but -CZ- stages are simpler and appear to be easier to implement compared to the -C- stages. Based on this decomposition, we develop a twoqubit gate depth-(14n−4) implementation of stabilizer circuits over the gate library {H, P, CNOT}, executable in the LNN architecture, improving best previously known depth-25n circuit, also executable in the LNN architecture. Our constructions rely on Bruhat decomposition of the symplectic group and on folding arbitrarily long sequences of the form (-P-C-) m into a 3-stage computation -P-CZ-C-. Our results include the reduction of the 11-stage decomposition -H-C-P-C-P-C-H-P-C-P-C- into a 9-stage decomposition of the form -C-P-C-P-H-C-P-C-P-. This reduction is based on the Bruhat decomposition of the symplectic group. This result also implies a new normal form for stabilizer circuits. We show that a circuit in this normal form is optimal in the number of Hadamard gates used. We also show that the normal form has an asymptotically optimal number of parameters.

1 aMaslov, Dmitri1 aRoetteler, Martin uhttps://arxiv.org/abs/1705.0917601534nas a2200169 4500008004100000245006200041210005800103260001500161490000800176520102300184100002301207700002201230700002301252700002501275700002701300856003701327 2017 eng d00aA solvable family of driven-dissipative many-body systems0 asolvable family of drivendissipative manybody systems c2017/11/100 v1193 a

Exactly solvable models have played an important role in establishing the sophisticated modern understanding of equilibrium many-body physics. And conversely, the relative scarcity of solutions for non-equilibrium models greatly limits our understanding of systems away from thermal equilibrium. We study a family of nonequilibrium models, some of which can be viewed as dissipative analogues of the transverse-field Ising model, in that an effectively classical Hamiltonian is frustrated by dissipative processes that drive the system toward states that do not commute with the Hamiltonian. Surprisingly, a broad and experimentally relevant subset of these models can be solved efficiently in any number of spatial dimensions. We leverage these solutions to prove a no-go theorem on steady-state phase transitions in a many-body model that can be realized naturally with Rydberg atoms or trapped ions, and to compute the effects of decoherence on a canonical trapped-ion-based quantum computation architecture.

1 aFoss-Feig, Michael1 aYoung, Jeremy, T.1 aAlbert, Victor, V.1 aGorshkov, Alexey, V.1 aMaghrebi, Mohammad, F. uhttps://arxiv.org/abs/1703.0462601530nas a2200217 4500008004100000245006000041210006000101260001500161300001100176490000800187520092200195100001501117700001601132700001601148700001101164700001901175700002101194700001901215700001801234856006001252 2017 eng d00aThreshold Dynamics of a Semiconductor Single Atom Maser0 aThreshold Dynamics of a Semiconductor Single Atom Maser c2017/08/31 a0977020 v1193 a

We demonstrate a single atom maser consisting of a semiconductor double quantum dot (DQD) that is embedded in a high-quality-factor microwave cavity. A finite bias drives the DQD out of equilibrium, resulting in sequential single electron tunneling and masing. We develop a dynamic tuning protocol that allows us to controllably increase the time-averaged repumping rate of the DQD at a fixed level detuning, and quantitatively study the transition through the masing threshold. We further examine the crossover from incoherent to coherent emission by measuring the photon statistics across the masing transition. The observed threshold behavior is in agreement with an existing single atom maser theory when small corrections from lead emission are taken into account.

1 aLiu, Y.-Y.1 aStehlik, J.1 aEichler, C.1 aMi, X.1 aHartke, T., R.1 aGullans, Michael1 aTaylor, J., M.1 aPetta, J., R. uhttps://link.aps.org/doi/10.1103/PhysRevLett.119.09770201731nas a2200133 4500008004100000245003500041210003500076260001500111520136800126100001901494700002501513700002201538856003701560 2017 eng d00aUnforgeable Quantum Encryption0 aUnforgeable Quantum Encryption c2017/09/193 a

We study the problem of encrypting and authenticating quantum data in the presence of adversaries making adaptive chosen plaintext and chosen ciphertext queries. Classically, security games use string copying and comparison to detect adversarial cheating in such scenarios. Quantumly, this approach would violate no-cloning. We develop new techniques to overcome this problem: we use entanglement to detect cheating, and rely on recent results for characterizing quantum encryption schemes. We give definitions for (i.) ciphertext unforgeability , (ii.) indistinguishability under adaptive chosen-ciphertext attack, and (iii.) authenticated encryption. The restriction of each definition to the classical setting is at least as strong as the corresponding classical notion: (i) implies INT-CTXT, (ii) implies IND-CCA2, and (iii) implies AE. All of our new notions also imply QIND-CPA privacy. Combining one-time authentication and classical pseudorandomness, we construct schemes for each of these new quantum security notions, and provide several separation examples. Along the way, we also give a new definition of one-time quantum authentication which, unlike all previous approaches, authenticates ciphertexts rather than plaintexts.

1 aAlagic, Gorjan1 aGagliardoni, Tommaso1 aMajenz, Christian uhttps://arxiv.org/abs/1709.0653901611nas a2200133 4500008004100000245008000041210006900121260001500190490000700205520118300212100001701395700001601412856004901428 2017 eng d00aUniversal Security for Randomness Expansion from the Spot-Checking Protocol0 aUniversal Security for Randomness Expansion from the SpotCheckin c2017/08/010 v463 a

Colbeck (Thesis, 2006) proposed using Bell inequality violations to generate certified random numbers. While full quantum-security proofs have been given, it remains a major open problem to identify the broadest class of Bell inequalities and lowest performance requirements to achieve such security. In this paper, working within the broad class of spot-checking protocols, we prove exactly which Bell inequality violations can be used to achieve full security. Our result greatly improves the known noise tolerance for secure randomness expansion: for the commonly used CHSH game, full security was only known with a noise tolerance of 1.5%, and we improve this to 10.3%. We also generalize our results beyond Bell inequalities and give the first security proof for randomness expansion based on Kochen-Specker inequalities. The central technical contribution of the paper is a new uncertainty principle for the Schatten norm, which is based on the uniform convexity inequality of Ball, Carlen, and Lieb (Inventiones mathematicae, 115:463-482, 1994).

1 aMiller, Carl1 aShi, Yaoyun uhttp://epubs.siam.org/doi/10.1137/15M104433300962nas a2200121 4500008004100000245007400041210006900115260001500184520054100199100001900740700001800759856006300777 2017 eng d00aUse of global interactions in efficient quantum circuit constructions0 aUse of global interactions in efficient quantum circuit construc c2017/12/213 a

In this paper we study the ways to use a global entangling operator to efficiently implement circuitry common to a selection of important quantum algorithms. In particular, we focus on the circuits composed with global Ising entangling gates and arbitrary addressable single-qubit gates. We show that under certain circumstances the use of global operations can substantially improve the entangling gate count.

1 aMaslov, Dmitri1 aNam, Yunseong uhttp://iopscience.iop.org/article/10.1088/1367-2630/aaa39801659nas a2200133 4500008004100000245011600041210006900157260001500226300001100241490000700252520121100259100001901470856003601489 2016 eng d00aOn the advantages of using relative phase Toffolis with an application to multiple control Toffoli optimization0 aadvantages of using relative phase Toffolis with an application  c2016/02/10 a0223110 v933 aVarious implementations of the Toffoli gate up to a relative phase have been known for years. The advantage over regular Toffoli gate is their smaller circuit size. However, their use has been often limited to a demonstration of quantum control in designs such as those where the Toffoli gate is being applied last or otherwise for some specific reasons the relative phase does not matter. It was commonly believed that the relative phase deviations would prevent the relative phase Toffolis from being very helpful in practical large-scale designs. In this paper, we report three circuit identities that provide the means for replacing certain configurations of the multiple control Toffoli gates with their simpler relative phase implementations, up to a selectable unitary on certain qubits, and without changing the overall functionality. We illustrate the advantage via applying those identities to the optimization of the known circuits implementing multiple control Toffoli gates, and report the reductions in the CNOT-count, T-count, as well as the number of ancillae used. We suggest that a further study of the relative phase Toffoli implementations and their use may yield other optimizations.1 aMaslov, Dmitri uhttp://arxiv.org/abs/1508.0327300514nas a2200157 4500008004100000245006700041210006600108260001500174300001100189490000700200100002700207700001900234700002300253700002500276856005500301 2016 eng d00aCausality and quantum criticality in long-range lattice models0 aCausality and quantum criticality in longrange lattice models c2016/03/17 a1251280 v931 aMaghrebi, Mohammad, F.1 aGong, Zhe-Xuan1 aFoss-Feig, Michael1 aGorshkov, Alexey, V. uhttp://link.aps.org/doi/10.1103/PhysRevB.93.12512801582nas a2200169 4500008004100000245006700041210006600108260001500174300001100189490000700200520107500207100002701282700001901309700002301328700002501351856003601376 2016 eng d00aCausality and quantum criticality with long-range interactions0 aCausality and quantum criticality with longrange interactions c2016/03/17 a1251280 v923 a Quantum lattice systems with long-range interactions often exhibit drastically different behavior than their short-range counterparts. In particular, because they do not satisfy the conditions for the Lieb-Robinson theorem, they need not have an emergent relativistic structure in the form of a light cone. Adopting a field-theoretic approach, we study the one-dimensional transverse-field Ising model and a fermionic model with long-range interactions, explore their critical and near-critical behavior, and characterize their response to local perturbations. We deduce the dynamic critical exponent, up to the two-loop order within the renormalization group theory, which we then use to characterize the emergent causal behavior. We show that beyond a critical value of the power-law exponent of long-range interactions, the dynamics effectively becomes relativistic. Various other critical exponents describing correlations in the ground state, as well as deviations from a linear causal cone, are deduced for a wide range of the power-law exponent. 1 aMaghrebi, Mohammad, F.1 aGong, Zhe-Xuan1 aFoss-Feig, Michael1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1508.0090601522nas a2200133 4500008004100000245007000041210006900111260001500180520109400195100002301289700001601312700002401328856003601352 2016 eng d00aCo-Designing a Scalable Quantum Computer with Trapped Atomic Ions0 aCoDesigning a Scalable Quantum Computer with Trapped Atomic Ions c2016/02/093 aThe first generation of quantum computers are on the horizon, fabricated from quantum hardware platforms that may soon be able to tackle certain tasks that cannot be performed or modelled with conventional computers. These quantum devices will not likely be universal or fully programmable, but special-purpose processors whose hardware will be tightly co-designed with particular target applications. Trapped atomic ions are a leading platform for first generation quantum computers, but are also fundamentally scalable to more powerful general purpose devices in future generations. This is because trapped ion qubits are atomic clock standards that can be made identical to a part in 10^15, and their quantum circuit connectivity can be reconfigured through the use of external fields, without modifying the arrangement or architecture of the qubits themselves. In this article we show how a modular quantum computer of any size can be engineered from ion crystals, and how the wiring between ion trap qubits can be tailored to a variety of applications and quantum computing protocols.1 aBrown, Kenneth, R.1 aKim, Jaewan1 aMonroe, Christopher uhttp://arxiv.org/abs/1602.0284001682nas a2200193 4500008004100000245006100041210006100102260001500163300001100178490000700189520113200196100002101328700002101349700001301370700002501383700002101408700002301429856003601452 2016 eng d00aCollective phases of strongly interacting cavity photons0 aCollective phases of strongly interacting cavity photons c2016/09/01 a0338010 v943 a

We study a coupled array of coherently driven photonic cavities, which maps onto a driven-dissipative XY spin-12 model with ferromagnetic couplings in the limit of strong optical nonlinearities. Using a site-decoupled mean-field approximation, we identify steady state phases with canted antiferromagnetic order, in addition to limit cycle phases, where oscillatory dynamics persist indefinitely. We also identify collective bistable phases, where the system supports two steady states among spatially uniform, antiferromagnetic, and limit cycle phases. We compare these mean-field results to exact quantum trajectories simulations for finite one-dimensional arrays. The exact results exhibit short-range antiferromagnetic order for parameters that have significant overlap with the mean-field phase diagram. In the mean-field bistable regime, the exact quantum dynamics exhibits real-time collective switching between macroscopically distinguishable states. We present a clear physical picture for this dynamics, and establish a simple relationship between the switching times and properties of the quantum Liouvillian.

1 aWilson, Ryan, M.1 aMahmud, Khan, W.1 aHu, Anzi1 aGorshkov, Alexey, V.1 aHafezi, Mohammad1 aFoss-Feig, Michael uhttp://arxiv.org/abs/1601.0685702040nas a2200193 4500008004100000245007800041210006900119260001500188300001000203490000800213520145000221100001601671700001801687700001601705700002101721700001501742700001501757856007401772 2016 eng d00aDemonstration of a small programmable quantum computer with atomic qubits0 aDemonstration of a small programmable quantum computer with atom c2016/08/04 a63-660 v5363 a

Quantum computers can solve certain problems more efficiently than any possible conventional computer. Small quantum algorithms have been demonstrated on multiple quantum computing platforms, many specifically tailored in hardware to implement a particular algorithm or execute a limited number of computational paths. Here, we demonstrate a five-qubit trapped-ion quantum computer that can be programmed in software to implement arbitrary quantum algorithms by executing any sequence of universal quantum logic gates. We compile algorithms into a fully-connected set of gate operations that are native to the hardware and have a mean fidelity of 98 %. Reconfiguring these gate sequences provides the flexibility to implement a variety of algorithms without altering the hardware. As examples, we implement the Deutsch-Jozsa (DJ) and Bernstein-Vazirani (BV) algorithms with average success rates of 95 % and 90 %, respectively. We also perform a coherent quantum Fourier transform (QFT) on five trappedion qubits for phase estimation and period finding with average fidelities of 62 % and 84 %, respectively. This small quantum computer can be scaled to larger numbers of qubits within a single register, and can be further expanded by connecting several such modules through ion shuttling or photonic quantum channels.

1 aDebnath, S.1 aLinke, N., M.1 aFiggatt, C.1 aLandsman, K., A.1 aWright, K.1 aMonroe, C. uhttp://www.nature.com/nature/journal/v536/n7614/full/nature18648.html01662nas a2200217 4500008004100000245004300041210004300084260001500127300001100142490000600153520108300159100001601242700001501258700001601273700001901289700001101308700002101319700001901340700001801359856006701377 2016 eng d00aDouble Quantum Dot Floquet Gain Medium0 aDouble Quantum Dot Floquet Gain Medium c2016/11/07 a0410270 v63 a

Strongly driving a two-level quantum system with light leads to a ladder of Floquet states separated by the photon energy. Nanoscale quantum devices allow the interplay of confined electrons, phonons, and photons to be studied under strong driving conditions. Here we show that a single electron in a periodically driven DQD functions as a "Floquet gain medium," where population imbalances in the DQD Floquet quasi-energy levels lead to an intricate pattern of gain and loss features in the cavity response. We further measure a large intra-cavity photon number n_c in the absence of a cavity drive field, due to equilibration in the Floquet picture. Our device operates in the absence of a dc current -- one and the same electron is repeatedly driven to the excited state to generate population inversion. These results pave the way to future studies of non-classical light and thermalization of driven quantum systems.

1 aStehlik, J.1 aLiu, Y.-Y.1 aEichler, C.1 aHartke, T., R.1 aMi, X.1 aGullans, Michael1 aTaylor, J., M.1 aPetta, J., R. uhttp://journals.aps.org/prx/abstract/10.1103/PhysRevX.6.04102701724nas a2200181 4500008004100000245005800041210005800099260001500157520121100172100001801383700001801401700002101419700001601440700001601456700001801472700001501490856003701505 2016 eng d00aExperimental demonstration of quantum fault tolerance0 aExperimental demonstration of quantum fault tolerance c2016/11/213 a

Quantum computers will eventually reach a size at which quantum error correction (QEC) becomes imperative. In order to make quantum information robust to errors introduced by qubit imperfections and flawed control operations, QEC protocols encode a logical qubit in multiple physical qubits. This redundancy allows the extraction of error syndromes and the subsequent correction or detection of errors without destroying the logical state itself through direct measurement. While several experiments have shown a reduction of high intrinsic or artificially introduced errors in logical qubits, fault-tolerant encoding of a logical qubit has never been demonstrated. Here we show the encoding and syndrome measurement of a fault-tolerant logical qubit via an error detection protocol on four physical qubits, represented by trapped atomic ions. This demonstrates for the first time the robustness of a fault-tolerant qubit to imperfections in the very operations used to encode it. This advantage persists in the face of large added error rates and experimental calibration errors.

1 aLinke, N., M.1 aGutierrez, M.1 aLandsman, K., A.1 aFiggatt, C.1 aDebnath, S.1 aBrown, K., R.1 aMonroe, C. uhttps://arxiv.org/abs/1611.0694601255nas a2200157 4500008004100000245006900041210006900110260001500179300001100194490000700205520078100212100002700993700002201020700001901042856003601061 2016 eng d00aFlight of a heavy particle nonlinearly coupled to a quantum bath0 aFlight of a heavy particle nonlinearly coupled to a quantum bath c2016/01/28 a0143090 v933 a Fluctuation and dissipation are by-products of coupling to the `environment.' The Caldeira-Leggett model, a successful paradigm of quantum Brownian motion, views the environment as a collection of harmonic oscillators linearly coupled to the system. However, symmetry considerations may forbid a linear coupling, e.g. for a neutral particle in quantum electrodynamics. We argue that nonlinear couplings can lead to a fundamentally different behavior. Specifically, we consider a heavy particle quadratically coupled to quantum fluctuations of the bath. In one dimension the particle undergoes anomalous diffusion, unfolding as a power-law distribution in space, reminiscent of L\'{e}vy flights. We suggest condensed matter analogs where similar effects may arise. 1 aMaghrebi, Mohammad, F.1 aKrüger, Matthias1 aKardar, Mehran uhttp://arxiv.org/abs/1508.0058201247nas a2200169 4500008004100000245005400041210005400095260001500149300001200164520072500176100002400901700002000925700002100945700001600966700001800982856007701000 2016 eng d00aHigh resolution adaptive imaging of a single atom0 aHigh resolution adaptive imaging of a single atom c2016/07/18 a606-6103 a

We report the optical imaging of a single atom with nanometer resolution using an adaptive optical alignment technique that is applicable to general optical microscopy. By decomposing the image of a single laser-cooled atom, we identify and correct optical aberrations in the system and realize an atomic position sensitivity of ≈ 0.5 nm/Hz−−−√ with a minimum uncertainty of 1.7 nm, allowing the direct imaging of atomic motion. This is the highest position sensitivity ever measured for an isolated atom, and opens up the possibility of performing out-of-focus 3D particle tracking, imaging of atoms in 3D optical lattices or sensing forces at the yoctonewton (10−24 N) scale.

1 aWong-Campos, J., D.1 aJohnson, K., G.1 aNeyenhuis, Brian1 aMizrahi, J.1 aMonroe, Chris uhttps://www.nature.com/nphoton/journal/v10/n9/full/nphoton.2016.136.html01814nas a2200205 4500008004100000245007600041210006900117260001500186300001100201490000700212520120100219100001901420700002701439700001301466700002301479700002101502700002401523700002501547856003601572 2016 eng d00aKaleidoscope of quantum phases in a long-range interacting spin-1 chain0 aKaleidoscope of quantum phases in a longrange interacting spin1  c2016/05/11 a2051150 v933 aMotivated by recent trapped-ion quantum simulation experiments, we carry out a comprehensive study of the phase diagram of a spin-1 chain with XXZ-type interactions that decay as 1/rα, using a combination of finite and infinite-size DMRG calculations, spin-wave analysis, and field theory. In the absence of long-range interactions, varying the spin-coupling anisotropy leads to four distinct phases: a ferromagnetic Ising phase, a disordered XY phase, a topological Haldane phase, and an antiferromagnetic Ising phase. If long-range interactions are antiferromagnetic and thus frustrated, we find primarily a quantitative change of the phase boundaries. On the other hand, ferromagnetic (non-frustrated) long-range interactions qualitatively impact the entire phase diagram. Importantly, for α≲3, long-range interactions destroy the Haldane phase, break the conformal symmetry of the XY phase, give rise to a new phase that spontaneously breaks a U(1) continuous symmetry, and introduce an exotic tricritical point with no direct parallel in short-range interacting spin chains. We show that the main signatures of all five phases found could be observed experimentally in the near future. 1 aGong, Zhe-Xuan1 aMaghrebi, Mohammad, F.1 aHu, Anzi1 aFoss-Feig, Michael1 aRicherme, Philip1 aMonroe, Christopher1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1510.0210801559nas a2200157 4500008004100000245008500041210006900126260001500195300001100210490000700221520104000228100002301268700002501291700001701316856006801333 2016 eng d00aMany-body decoherence dynamics and optimised operation of a single-photon switch0 aManybody decoherence dynamics and optimised operation of a singl c2016/09/13 a0920010 v183 a

We develop a theoretical framework to characterize the decoherence dynamics due to multi-photon scattering in an all-optical switch based on Rydberg atom induced nonlinearities. By incorporating the knowledge of this decoherence process into optimal photon storage and retrieval strategies, we establish optimised switching protocols for experimentally relevant conditions, and evaluate the corresponding limits in the achievable fidelities. Based on these results we work out a simplified description that reproduces recent experiments [arXiv:1511.09445] and provides a new interpretation in terms of many-body decoherence involving multiple incident photons and multiple gate excitations forming the switch. Aside from offering insights into the operational capacity of realistic photon switching capabilities, our work provides a complete description of spin wave decoherence in a Rydberg quantum optics setting, and has immediate relevance to a number of further applications employing photon storage in Rydberg media. 

1 aMurray, Callum, R.1 aGorshkov, Alexey, V.1 aPohl, Thomas uhttp://iopscience.iop.org/article/10.1088/1367-2630/18/9/09200102166nas a2200205 4500008004100000245008500041210006900126260001500195520153900210100001701749700001501766700002101781700002101802700001901823700001901842700001701861700002001878700002401898856003801922 2016 eng d00aMany-body localization in a quantum simulator with programmable random disorder0 aManybody localization in a quantum simulator with programmable r c2016/06/063 a

When a system thermalizes it loses all local memory of its initial conditions. This is a general feature of open systems and is well described by equilibrium statistical mechanics. Even within a closed (or reversible) quantum system, where unitary time evolution retains all information about its initial state, subsystems can still thermalize using the rest of the system as an effective heat bath. Exceptions to quantum thermalization have been predicted and observed, but typically require inherent symmetries or noninteracting particles in the presence of static disorder. The prediction of many-body localization (MBL), in which disordered quantum systems can fail to thermalize in spite of strong interactions and high excitation energy, was therefore surprising and has attracted considerable theoretical attention. Here we experimentally generate MBL states by applying an Ising Hamiltonian with long-range interactions and programmably random disorder to ten spins initialized far from equilibrium. We observe the essential signatures of MBL: memory retention of the initial state, a Poissonian distribution of energy level spacings, and entanglement growth in the system at long times. Our platform can be scaled to higher numbers of spins, where detailed modeling of MBL becomes impossible due to the complexity of representing such entangled quantum states. Moreover, the high degree of control in our experiment may guide the use of MBL states as potential quantum memories in naturally disordered quantum systems.

1 aSmith, Jacob1 aLee, Aaron1 aRicherme, Philip1 aNeyenhuis, Brian1 aHess, Paul, W.1 aHauke, Philipp1 aHeyl, Markus1 aHuse, David, A.1 aMonroe, Christopher uhttp://arxiv.org/abs/1508.07026v102179nas a2200157 4500008004100000245010300041210006900144520165700213100002001870700001901890700001901909700001701928700002501945700001501970856003601985 2016 eng d00aMapping constrained optimization problems to quantum annealing with application to fault diagnosis0 aMapping constrained optimization problems to quantum annealing w3 aCurrent quantum annealing (QA) hardware suffers from practical limitations such as finite temperature, sparse connectivity, small qubit numbers, and control error. We propose new algorithms for mapping boolean constraint satisfaction problems (CSPs) onto QA hardware mitigating these limitations. In particular we develop a new embedding algorithm for mapping a CSP onto a hardware Ising model with a fixed sparse set of interactions, and propose two new decomposition algorithms for solving problems too large to map directly into hardware. The mapping technique is locally-structured, as hardware compatible Ising models are generated for each problem constraint, and variables appearing in different constraints are chained together using ferromagnetic couplings. In contrast, global embedding techniques generate a hardware independent Ising model for all the constraints, and then use a minor-embedding algorithm to generate a hardware compatible Ising model. We give an example of a class of CSPs for which the scaling performance of D-Wave's QA hardware using the local mapping technique is significantly better than global embedding. We validate the approach by applying D-Wave's hardware to circuit-based fault-diagnosis. For circuits that embed directly, we find that the hardware is typically able to find all solutions from a min-fault diagnosis set of size N using 1000N samples, using an annealing rate that is 25 times faster than a leading SAT-based sampling method. Further, we apply decomposition algorithms to find min-cardinality faults for circuits that are up to 5 times larger than can be solved directly on current hardware.1 aBian, Zhengbing1 aChudak, Fabian1 aIsrael, Robert1 aLackey, Brad1 aMacready, William, G1 aRoy, Aidan uhttp://arxiv.org/abs/1603.0311103037nas a2200193 4500008004100000245010200041210006900143260001500212300000700227490000600234520240900240100002002649700001902669700002602688700001702714700002502731700001502756856007202771 2016 eng d00aMapping contrained optimization problems to quantum annealing with application to fault diagnosis0 aMapping contrained optimization problems to quantum annealing wi c2016/07/28 a140 v33 a

Current quantum annealing (QA) hardware suffers from practical limitations such as finite temperature, sparse connectivity, small qubit numbers, and control error. We propose new algorithms for mapping Boolean constraint satisfaction problems (CSPs) onto QA hardware mitigating these limitations. In particular, we develop a new embedding algorithm for mapping a CSP onto a hardware Ising model with a fixed sparse set of interactions and propose two new decomposition algorithms for solving problems too large to map directly into hardware. The mapping technique is locally structured, as hardware compatible Ising models are generated for each problem constraint, and variables appearing in different constraints are chained together using ferromagnetic couplings. By contrast, global embedding techniques generate a hardware-independent Ising model for all the constraints, and then use a minor-embedding algorithm to generate a hardware compatible Ising model. We give an example of a class of CSPs for which the scaling performance of the D-Wave hardware using the local mapping technique is significantly better than global embedding. We validate the approach by applying D- Wave’s QA hardware to circuit-based fault diagnosis. For circuits that embed directly, we find that the hardware is typically able to find all solutions from a min-fault diagnosis set of size N using 1000 N samples, using an annealing rate that is 25 times faster than a leading SAT-based sampling method. Furthermore, we apply decomposition algorithms to find min-cardinality faults for circuits that are up to 5 times larger than can be solved directly on current hardware.

1 aBian, Zhengbing1 aChudak, Fabian1 aIsrael, Robert, Brian1 aLackey, Brad1 aMacready, William, G1 aRoy, Aiden uhttp://journal.frontiersin.org/article/10.3389/fict.2016.00014/full01599nas a2200145 4500008004100000245006500041210006400106260001500170300001100185490000700196520116200203100002701365700002501392856003601417 2016 eng d00aNonequilibrium many-body steady states via Keldysh formalism0 aNonequilibrium manybody steady states via Keldysh formalism c2016/01/27 a0143070 v933 a Many-body systems with both coherent dynamics and dissipation constitute a rich class of models which are nevertheless much less explored than their dissipationless counterparts. The advent of numerous experimental platforms that simulate such dynamics poses an immediate challenge to systematically understand and classify these models. In particular, nontrivial many-body states emerge as steady states under non-equilibrium dynamics. While these states and their phase transitions have been studied extensively with mean field theory, the validity of the mean field approximation has not been systematically investigated. In this paper, we employ a field-theoretic approach based on the Keldysh formalism to study nonequilibrium phases and phase transitions in a variety of models. In all cases, a complete description via the Keldysh formalism indicates a partial or complete failure of the mean field analysis. Furthermore, we find that an effective temperature emerges as a result of dissipation, and the universal behavior including the dynamics near the steady state is generically described by a thermodynamic universality class. 1 aMaghrebi, Mohammad, F.1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1507.0193902050nas a2200205 4500008004100000245008900041210006900130260001500199520143900214100001801653700001401671700001601685700001401701700001701715700001701732700001801749700002501767700001501792856003701807 2016 eng d00a{O}bservation of {P}rethermalization in {L}ong-{R}ange {I}nteracting {S}pin {C}hains0 aO bservation of P rethermalization in L ong R ange I nteracting  c2016/08/023 a

Statistical mechanics can predict thermal equilibrium states for most classical systems, but for an isolated quantum system there is no general understanding on how equilibrium states dynamically emerge from the microscopic Hamiltonian. For instance, quantum systems that are near-integrable usually fail to thermalize in an experimentally realistic time scale and, instead, relax to quasi-stationary prethermal states that can be described by statistical mechanics when approximately conserved quantities are appropriately included in a generalized Gibbs ensemble (GGE). Here we experimentally study the relaxation dynamics of a chain of up to 22 spins evolving under a long-range transverse field Ising Hamiltonian following a sudden quench. For sufficiently long-ranged interactions the system relaxes to a new type of prethermal state that retains a strong memory of the initial conditions. In this case, the prethermal state cannot be described by a GGE, but rather arises from an emergent double-well potential felt by the spin excitations. This result shows that prethermalization occurs in a significantly broader context than previously thought, and reveals new challenges for a generic understanding of the thermalization of quantum systems, particularly in the presence of long-range interactions.

1 aNeyenhuis, B.1 aSmith, J.1 aLee, A., C.1 aZhang, J.1 aRicherme, P.1 aHess, P., W.1 aGong, Z., -X.1 aGorshkov, Alexey, V.1 aMonroe, C. uhttps://arxiv.org/abs/1608.0068100852nas a2200133 4500008004100000245008100041210006900122260001500191300001400206490000700220520043600227100001900663856003600682 2016 eng d00aOptimal and asymptotically optimal NCT reversible circuits by the gate types0 aOptimal and asymptotically optimal NCT reversible circuits by th c2016/08/23 a1096-11120 v163 a

We report optimal and asymptotically optimal reversible circuits composed of NOT, CNOT, and Toffoli (NCT) gates, keeping the count by the subsets of the gate types used. This study fine tunes the circuit complexity figures for the realization of reversible functions via reversible NCT circuits. An important consequence is a result on the limitation of the use of the T-count quantum circuit metric popular in applications.

1 aMaslov, Dmitri uhttp://arxiv.org/abs/1602.0262701464nas a2200169 4500008004100000022001400041245010200055210006900157260001500226300001400241490000700255520082200262100002301084700001901107700001901126856014901145 2016 eng d a0018-934000aPractical Approximation of Single-Qubit Unitaries by Single-Qubit Quantum Clifford and T Circuits0 aPractical Approximation of SingleQubit Unitaries by SingleQubit  c2016/01/01 a161 - 1720 v653 a

We present an algorithm, along with its implementation that finds T-optimal approximations of single-qubit Z-rotations using quantum circuits consisting of Clifford and T gates. Our algorithm is capable of handling errors in approximation down to size 10-15, resulting in the optimal single-qubit circuit designs required for implementation of scalable quantum algorithms. Our implementation along with the experimental results are available in the public domain.

1 aKliuchnikov, Vadym1 aMaslov, Dmitri1 aMosca, Michele uhttp://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=7056491http://xplorestaging.ieee.org/ielx7/12/7350319/7056491.pdf?arnumber=705649101933nas a2200277 4500008004100000245007200041210006900113260001500182300001100197490000700208520116900215100001301384700001901397700001401416700001801430700001401448700002501462700002301487700001701510700001701527700002101544700001801565700001401583700002201597856003601619 2016 eng d00aPure-state tomography with the expectation value of Pauli operators0 aPurestate tomography with the expectation value of Pauli operato c2016/03/31 a0321400 v933 a

We examine the problem of finding the minimum number of Pauli measurements needed to uniquely determine an arbitrary n-qubit pure state among all quantum states. We show that only 11 Pauli measurements are needed to determine an arbitrary two-qubit pure state compared to the full quantum state tomography with 16 measurements, and only 31 Pauli measurements are needed to determine an arbitrary three-qubit pure state compared to the full quantum state tomography with 64 measurements. We demonstrate that our protocol is robust under depolarizing error with simulated random pure states. We experimentally test the protocol on two- and three-qubit systems with nuclear magnetic resonance techniques. We show that the pure state tomography protocol saves us a number of measurements without considerable loss of fidelity. We compare our protocol with same-size sets of randomly selected Pauli operators and find that our selected set of Pauli measurements significantly outperforms those random sampling sets. As a direct application, our scheme can also be used to reduce the number of settings needed for pure-state tomography in quantum optical systems.

1 aMa, Xian1 aJackson, Tyler1 aZhou, Hui1 aChen, Jianxin1 aLu, Dawei1 aMazurek, Michael, D.1 aFisher, Kent, A.G.1 aPeng, Xinhua1 aKribs, David1 aResch, Kevin, J.1 aJi, Zhengfeng1 aZeng, Bei1 aLaflamme, Raymond uhttp://arxiv.org/abs/1601.0537901353nas a2200181 4500008004100000245006400041210006200105260001500167490000700182520077900189100002700968700001900995700002401014700002301038700001701061700002501078856006801103 2016 eng d00aRealizing Exactly Solvable SU(N) Magnets with Thermal Atoms0 aRealizing Exactly Solvable SUN Magnets with Thermal Atoms c2016/05/060 v933 a

We show that n thermal fermionic alkaline-earth-metal atoms in a flat-bottom trap allow one to robustly implement a spin model displaying two symmetries: the Sn symmetry that permutes atoms occupying different vibrational levels of the trap and the SU(N) symmetry associated with N nuclear spin states. The symmetries make the model exactly solvable, which, in turn, enables the analytic study of dynamical processes such as spin diffusion in this SU(N) system. We also show how to use this system to generate entangled states that allow for Heisenberg-limited metrology. This highly symmetric spin model should be experimentally realizable even when the vibrational levels are occupied according to a high-temperature thermal or an arbitrary nonthermal distribution.

1 aBeverland, Michael, E.1 aAlagic, Gorjan1 aMartin, Michael, J.1 aKoller, Andrew, P.1 aRey, Ana, M.1 aGorshkov, Alexey, V. uhttp://journals.aps.org/pra/abstract/10.1103/PhysRevA.93.05160102103nas a2200229 4500008004100000022001400041245010900055210006900164260001500233300001700248490000700265520140200272653002101674653001901695653001201714653002501726653002901751653002101780100001701801700001601818856003901834 2016 eng d a0004-541100aRobust Protocols for Securely Expanding Randomness and Distributing Keys Using Untrusted Quantum Devices0 aRobust Protocols for Securely Expanding Randomness and Distribut c2016/10/26 a33:1–33:630 v633 a

Randomness is a vital resource for modern-day information processing, especially for cryptography. A wide range of applications critically rely on abundant, high-quality random numbers generated securely. Here, we show how to expand a random seed at an exponential rate without trusting the underlying quantum devices. Our approach is secure against the most general adversaries, and has the following new features: cryptographic level of security, tolerating a constant level of imprecision in devices, requiring only unit size quantum memory (for each device component) in an honest implementation, and allowing a large natural class of constructions for the protocol. In conjunction with a recent work by Chung et al. [2014], it also leads to robust unbounded expansion using just 2 multipart devices. When adapted for distributing cryptographic keys, our method achieves, for the first time, exponential expansion combined with cryptographic security and noise tolerance. The proof proceeds by showing that the Rényi divergence of the outputs of the protocol (for a specific bounding operator) decreases linearly as the protocol iterates. At the heart of the proof are a new uncertainty principle on quantum measurements and a method for simulating trusted measurements with untrusted devices.

10akey distribution10anonlocal games10aprivacy10aquantum cryptography10arandom-number generation10auntrusted device1 aMiller, Carl1 aShi, Yaoyun uhttp://doi.acm.org/10.1145/288549321161nas a2200205 45000080041000000200022000410220014000632450069000772100068001462600015002143000016002294900007002455202053400252100002020786700002420806700002420830700002220854700002520876856005420901 2016 eng d a978-3-95977-013-2 a1868-896900aSpace-Efficient Error Reduction for Unitary Quantum Computations0 aSpaceEfficient Error Reduction for Unitary Quantum Computations c2016/04/27 a14:1--14:140 v553 a

This paper develops general space-efficient methods for error reduction for unitary quantum computation. Consider a polynomial-time quantum computation with completeness c and soundnesss, either with or without a witness (corresponding to QMA and BQP, respectively). To convert this computation into a new computation with error at most 2p, the most space-efficient method known requires extra workspace of O(plog1cs) qubits. This space requirement is too large for scenarios like logarithmic-space quantum computations. This paper presents error-reduction methods for unitary quantum computations (i.e., computations without intermediate measurements) that require extra workspace of just O(logpcs) qubits. This in particular gives the first methods of strong amplification for logarithmic-space unitary quantum computations with two-sided bounded error. This also leads to a number of consequences in complexity theory, such as the uselessness of quantum witnesses in bounded-error logarithmic-space unitary quantum computations, the PSPACE upper bound for QMA with exponentially-small completeness-soundness gap, and strong amplification for matchgate computations.

1 aFefferman, Bill1 aKobayashi, Hirotada1 aLin, Cedric, Yen-Yu1 aMorimae, Tomoyuki1 aNishimura, Harumichi uhttp://drops.dagstuhl.de/opus/volltexte/2016/629701747nas a2200157 4500008004100000245008800041210006900129260001500198300001100213490000700224520127000231100001801501700001501519700001901534856003601553 2016 eng d00aSudden-quench dynamics of Bardeen-Cooper-Schrieffer states in deep optical lattices0 aSuddenquench dynamics of BardeenCooperSchrieffer states in deep  c2016/08/05 a0236070 v943 a

We determine the exact time evolution of an initial Bardeen-Cooper-Schrieffer (BCS) state of ultra-cold atoms in a hexagonal optical lattice. The dynamical evolution is triggered by ramping the lattice potential up, such that the interaction strength Uf is much larger than the hopping amplitude Jf. The quench initiates collective oscillations with frequency |Uf|/(2π) in the momentum occupation numbers and imprints an oscillating phase with the same frequency on the order parameter Δ. The latter is not reproduced by treating the time evolution in mean-field theory. The momentum density-density or noise correlation functions oscillate at frequency |Uf|/2π as well as its second harmonic. For a very deep lattice, with negligible tunneling energy, the oscillations of momentum occupation numbers are undamped. Non-zero tunneling after the quench leads to dephasing of the different momentum modes and a subsequent damping of the oscillations. This occurs even for a finite-temperature initial BCS state, but not for a non-interacting Fermi gas. We therefore propose to use this dephasing to detect a BCS state. Finally, we predict that the noise correlation functions in a honeycomb lattice will develop strong anti-correlations near the Dirac point.

1 aNuske, Marlon1 aMathey, L.1 aTiesinga, Eite uhttp://arxiv.org/abs/1602.0097901535nas a2200193 4500008004100000245005200041210005100093260001500144300001100159490000700170520099900177100001901176700002701195700001301222700002201235700002301257700002501280856003601305 2016 eng d00aTopological phases with long-range interactions0 aTopological phases with longrange interactions c2016/01/08 a0411020 v933 a Topological phases of matter are primarily studied in quantum many-body systems with short-range interactions. Whether various topological phases can survive in the presence of long-range interactions, however, is largely unknown. Here we show that a paradigmatic example of a symmetry-protected topological phase, the Haldane phase of an antiferromagnetic spin-1 chain, surprisingly remains intact in the presence of arbitrarily slowly decaying power-law interactions. The influence of long-range interactions on the topological order is largely quantitative, and we expect similar results for more general systems. Our conclusions are based on large-scale matrix-product-state simulations and two complementary effective-field-theory calculations. The striking agreement between the numerical and analytical results rules out finite-size effects. The topological phase considered here should be experimentally observable in a recently developed trapped-ion quantum simulator. 1 aGong, Zhe-Xuan1 aMaghrebi, Mohammad, F.1 aHu, Anzi1 aWall, Michael, L.1 aFoss-Feig, Michael1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1505.0314601241nas a2200157 4500008004100000245005800041210005800099260001500157300001100172490000700183520080300190100001400993700002001007700001901027856003701046 2015 eng d00aBounds on quantum communication via Newtonian gravity0 aBounds on quantum communication via Newtonian gravity c2015/01/15 a0150060 v173 aNewtonian gravity yields specific observable consequences, the most striking of which is the emergence of a $1/r^2$ force. In so far as communication can arise via such interactions between distant particles, we can ask what would be expected for a theory of gravity that only allows classical communication. Many heuristic suggestions for gravity-induced decoherence have this restriction implicitly or explicitly in their construction. Here we show that communication via a $1/r^2$ force has a minimum noise induced in the system when the communication cannot convey quantum information, in a continuous time analogue to Bell's inequalities. Our derived noise bounds provide tight constraints from current experimental results on any theory of gravity that does not allow quantum communication. 1 aKafri, D.1 aMilburn, G., J.1 aTaylor, J., M. uhttp://arxiv.org/abs/1404.3214v201576nas a2200133 4500008004100000245010700041210006900148260001500217520110300232100002701335700001901362700002501381856003601406 2015 eng d00aContinuous symmetry breaking and a new universality class in 1D long-range interacting quantum systems0 aContinuous symmetry breaking and a new universality class in 1D  c2015/10/053 aContinuous symmetry breaking (CSB) in low-dimensional systems, forbidden by the Mermin-Wagner theorem for short-range interactions, may take place in the presence of slowly decaying long-range interactions. Nevertheless, there is no stringent bound on how slowly interactions should decay to give rise to CSB in 1D quantum systems at zero temperature. Here, we study a long-range interacting spin chain with U(1) symmetry and power-law interactions V(r)∼1/rα, directly relevant to ion-trap experiments. Using bosonization and renormalization group theory, we find CSB for α smaller than a critical exponent αc(≤3) depending on the microscopic parameters of the model. Furthermore, the transition from the gapless XY phase to the gapless CSB phase is mediated by the breaking of conformal symmetry due to long-range interactions, and is described by a new universality class akin to the Berezinskii-Kosterlitz-Thouless transition. Our analytical findings are in good agreement with a numerical calculation. Signatures of the CSB phase should be accessible in existing trapped-ion experiments.1 aMaghrebi, Mohammad, F.1 aGong, Zhe-Xuan1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1510.0132501507nas a2200229 4500008004100000245005700041210005700098260001500155300001100170490000800181520087400189100002701063700002101090700001601111700001301127700001501140700002001155700001801175700002101193700002501214856003801239 2015 eng d00aCoulomb bound states of strongly interacting photons0 aCoulomb bound states of strongly interacting photons c2015/09/16 a1236010 v1153 a We show that two photons coupled to Rydberg states via electromagnetically induced transparency can interact via an effective Coulomb potential. This interaction gives rise to a continuum of two-body bound states. Within the continuum, metastable bound states are distinguished in analogy with quasi-bound states tunneling through a potential barrier. We find multiple branches of metastable bound states whose energy spectrum is governed by the Coulomb potential, thus obtaining a photonic analogue of the hydrogen atom. Under certain conditions, the wavefunction resembles that of a diatomic molecule in which the two polaritons are separated by a finite "bond length." These states propagate with a negative group velocity in the medium, allowing for a simple preparation and detection scheme, before they slowly decay to pairs of bound Rydberg atoms. 1 aMaghrebi, Mohammad, F.1 aGullans, Michael1 aBienias, P.1 aChoi, S.1 aMartin, I.1 aFirstenberg, O.1 aLukin, M., D.1 aBüchler, H., P.1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1505.03859v101233nas a2200145 4500008004100000245009700041210006900138260001500207300001100222490000800233520076600241100002701007700001601034856003701050 2015 eng d00aEntanglement entropy of dispersive media from thermodynamic entropy in one higher dimension0 aEntanglement entropy of dispersive media from thermodynamic entr c2015/04/16 a1516020 v1143 a A dispersive medium becomes entangled with zero-point fluctuations in the vacuum. We consider an arbitrary array of material bodies weakly interacting with a quantum field and compute the quantum mutual information between them. It is shown that the mutual information in D dimensions can be mapped to classical thermodynamic entropy in D+1 dimensions. As a specific example, we compute the mutual information both analytically and numerically for a range of separation distances between two bodies in D=2 dimensions and find a logarithmic correction to the area law at short separations. A key advantage of our method is that it allows the strong subadditivity property---notoriously difficult to prove for quantum systems---to be easily verified. 1 aMaghrebi, Mohammad, F.1 aReid, Homer uhttp://arxiv.org/abs/1412.5613v201270nas a2200193 4500008004100000245005700041210005700098260001500155300001100170490000700181520071900188100002700907700002000934700002100954700001700975700002200992700002501014856003701039 2015 eng d00aFractional Quantum Hall States of Rydberg Polaritons0 aFractional Quantum Hall States of Rydberg Polaritons c2015/03/31 a0338380 v913 a We propose a scheme for realizing fractional quantum Hall states of light. In our scheme, photons of two polarizations are coupled to different atomic Rydberg states to form two flavors of Rydberg polaritons that behave as an effective spin. An array of optical cavity modes overlapping with the atomic cloud enables the realization of an effective spin-1/2 lattice. We show that the dipolar interaction between such polaritons, inherited from the Rydberg states, can be exploited to create a flat, topological band for a single spin-flip excitation. At half filling, this gives rise to a photonic (or polaritonic) fractional Chern insulator -- a lattice-based, fractional quantum Hall state of light. 1 aMaghrebi, Mohammad, F.1 aYao, Norman, Y.1 aHafezi, Mohammad1 aPohl, Thomas1 aFirstenberg, Ofer1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1411.6624v101328nas a2200157 4500008004100000245008400041210006900125260001500194300001100209490000700220520085400227100001801081700001901099700001501118856003701133 2015 eng d00aOptimization of collisional Feshbach cooling of an ultracold nondegenerate gas0 aOptimization of collisional Feshbach cooling of an ultracold non c2015/04/20 a0436260 v913 a We optimize a collision-induced cooling process for ultracold atoms in the nondegenerate regime. It makes use of a Feshbach resonance, instead of rf radiation in evaporative cooling, to selectively expel hot atoms from a trap. Using functional minimization we analytically show that for the optimal cooling process the resonance energy must be tuned such that it linearly follows the temperature. Here, optimal cooling is defined as maximizing the phase-space density after a fixed cooling duration. The analytical results are confirmed by numerical Monte-Carlo simulations. In order to simulate more realistic experimental conditions, we show that background losses do not change our conclusions, while additional non-resonant two-body losses make a lower initial resonance energy with non-linear dependence on temperature preferable. 1 aNuske, Marlon1 aTiesinga, Eite1 aMathey, L. uhttp://arxiv.org/abs/1412.8473v101186nas a2200181 4500008004100000245004300041210004300084260001500127300000800142490000700150520060900157100002300766700003000789700001800819700001900837700001900856856012900875 2015 eng d00aOptomechanical reference accelerometer0 aOptomechanical reference accelerometer c2015/09/08 a6540 v523 a

We present an optomechanical accelerometer with high dynamic range, high bandwidth and read-out noise levels below 8 ${\mu}$g/$\sqrt{\mathrm{Hz}}$. The straightforward assembly and low cost of our device make it a prime candidate for on-site reference calibrations and autonomous navigation. We present experimental data taken with a vacuum sealed, portable prototype and deduce the achieved bias stability and scale factor accuracy. Additionally, we present a comprehensive model of the device physics that we use to analyze the fundamental noise sources and accuracy limitations of such devices.

1 aGerberding, Oliver1 aCervantes, Felipe, Guzman1 aMelcher, John1 aPratt, Jon, R.1 aTaylor, J., M. uhttp://iopscience.iop.org/article/10.1088/0026-1394/52/5/654/meta;jsessionid=C2B417A5CD50B9B57EE14C78E1783802.ip-10-40-1-10501362nas a2200181 4500008004100000245005800041210005800099260001500157300001100172490000800183520083900191100002701030700002101057700002201078700002501100700001701125856003801142 2015 eng d00aParafermionic zero modes in ultracold bosonic systems0 aParafermionic zero modes in ultracold bosonic systems c2015/08/06 a0653010 v1153 a Exotic topologically protected zero modes with parafermionic statistics (also called fractionalized Majorana modes) have been proposed to emerge in devices fabricated from a fractional quantum Hall system and a superconductor. The fractionalized statistics of these modes takes them an important step beyond the simplest non-Abelian anyons, Majorana fermions. Building on recent advances towards the realization of fractional quantum Hall states of bosonic ultracold atoms, we propose a realization of parafermions in a system consisting of Bose-Einstein-condensate trenches within a bosonic fractional quantum Hall state. We show that parafermionic zero modes emerge at the endpoints of the trenches and give rise to a topologically protected degeneracy. We also discuss methods for preparing and detecting these modes. 1 aMaghrebi, Mohammad, F.1 aGaneshan, Sriram1 aClarke, David, J.1 aGorshkov, Alexey, V.1 aSau, Jay, D. uhttp://arxiv.org/abs/1504.04012v201945nas a2200205 4500008004100000245007600041210006900117260001500186300001100201490000700212520133700219100001901556700001901575700001901594700002401613700002701637700001801664700001901682856003801701 2015 eng d00aSelf-heterodyne detection of the {\it in-situ} phase of an atomic-SQUID0 aSelfheterodyne detection of the it insitu phase of an atomicSQUI c2015/09/03 a0336020 v923 a We present theoretical and experimental analysis of an interferometric measurement of the {\it in-situ} phase drop across and current flow through a rotating barrier in a toroidal Bose-Einstein condensate (BEC). This experiment is the atomic analog of the rf-superconducting quantum interference device (SQUID). The phase drop is extracted from a spiral-shaped density profile created by the spatial interference of the expanding toroidal BEC and a reference BEC after release from all trapping potentials. We characterize the interferometer when it contains a single particle, which is initially in a coherent superposition of a torus and reference state, as well as when it contains a many-body state in the mean-field approximation. The single-particle picture is sufficient to explain the origin of the spirals, to relate the phase-drop across the barrier to the geometry of a spiral, and to bound the expansion times for which the {\it in-situ} phase can be accurately determined. Mean-field estimates and numerical simulations show that the inter-atomic interactions shorten the expansion time scales compared to the single-particle case. Finally, we compare the mean-field simulations with our experimental data and confirm that the interferometer indeed accurately measures the {\it in-situ} phase drop. 1 aMathew, Ranchu1 aKumar, Avinash1 aEckel, Stephen1 aJendrzejewski, Fred1 aCampbell, Gretchen, K.1 aEdwards, Mark1 aTiesinga, Eite uhttp://arxiv.org/abs/1506.09149v201005nas a2200157 4500008004100000245006000041210005800101260001500159300001100174490000700185520056500192100001400757700001900771700002000790856003700810 2014 eng d00aA classical channel model for gravitational decoherence0 aclassical channel model for gravitational decoherence c2014/06/26 a0650200 v163 aWe show that, by treating the gravitational interaction between two mechanical resonators as a classical measurement channel, a gravitational decoherence model results that is equivalent to a model first proposed by Diosi. The resulting decoherence model implies that the classically mediated gravitational interaction between two gravitationally coupled resonators cannot create entanglement. The gravitational decoherence rate ( and the complementary heating rate) is of the order of the gravitationally induced normal mode splitting of the two resonators. 1 aKafri, D.1 aTaylor, J., M.1 aMilburn, G., J. uhttp://arxiv.org/abs/1401.0946v101375nas a2200193 4500008004100000245007300041210006900114260002600183300000700209490000600216520073500222100002000957700001900977700001900996700001701015700002501032700001501057856010901072 2014 eng d00aDiscrete optimization using quantum annealing on sparse Ising models0 aDiscrete optimization using quantum annealing on sparse Ising mo bFrontiersc2014/09/01 a560 v23 aThis paper discusses techniques for solving discrete optimization problems using quantum annealing. Practical issues likely to affect the computation include precision limitations, finite temperature, bounded energy range, sparse connectivity, and small numbers of qubits. To address these concerns we propose a way of finding energy representations with large classical gaps between ground and first excited states, efficient algorithms for mapping non-compatible Ising models into the hardware, and the use of decomposition methods for problems that are too large to fit in hardware. We validate the approach by describing experiments with D-Wave quantum hardware for low density parity check decoding with up to 1000 variables.1 aBian, Zhengbing1 aChudak, Fabian1 aIsrael, Robert1 aLackey, Brad1 aMacready, William, G1 aRoy, Aidan uhttps://www.quics.umd.edu/publications/discrete-optimization-using-quantum-annealing-sparse-ising-models02029nas a2200241 4500008004100000245006600041210006500107260001400172490000800186520133800194100002601532700001801558700002301576700001201599700002201611700002101633700002001654700002301674700001201697700002101709700002001730856003701750 2014 eng d00aMany-body dynamics of dipolar molecules in an optical lattice0 aManybody dynamics of dipolar molecules in an optical lattice c2014/11/70 v1133 a Understanding the many-body dynamics of isolated quantum systems is one of the central challenges in modern physics. To this end, the direct experimental realization of strongly correlated quantum systems allows one to gain insights into the emergence of complex phenomena. Such insights enable the development of theoretical tools that broaden our understanding. Here, we theoretically model and experimentally probe with Ramsey spectroscopy the quantum dynamics of disordered, dipolar-interacting, ultracold molecules in a partially filled optical lattice. We report the capability to control the dipolar interaction strength, and we demonstrate that the many-body dynamics extends well beyond a nearest-neighbor or mean-field picture, and cannot be quantitatively described using previously available theoretical tools. We develop a novel cluster expansion technique and demonstrate that our theoretical method accurately captures the measured dependence of the spin dynamics on molecule number and on the dipolar interaction strength. In the spirit of quantum simulation, this agreement simultaneously benchmarks the new theoretical method and verifies our microscopic understanding of the experiment. Our findings pave the way for numerous applications in quantum information science, metrology, and condensed matter physics. 1 aHazzard, Kaden, R. A.1 aGadway, Bryce1 aFoss-Feig, Michael1 aYan, Bo1 aMoses, Steven, A.1 aCovey, Jacob, P.1 aYao, Norman, Y.1 aLukin, Mikhail, D.1 aYe, Jun1 aJin, Deborah, S.1 aRey, Ana, Maria uhttp://arxiv.org/abs/1402.2354v101828nas a2200145 4500008004100000245015000041210006900191260001400260490000700274520129600281100002701577700002201604700001901626856003701645 2014 eng d00aNonequilibrium quantum fluctuations of a dispersive medium: Spontaneous emission, photon statistics, entropy generation, and stochastic motion 0 aNonequilibrium quantum fluctuations of a dispersive medium Spont c2014/7/160 v903 a We study the implications of quantum fluctuations of a dispersive medium, under steady rotation, either in or out of thermal equilibrium with its environment. A rotating object exhibits a quantum instability by dissipating its mechanical motion via spontaneous emission of photons, as well as internal heat generation. Universal relations are derived for the radiated energy and angular momentum as trace formulas involving the object's scattering matrix. We also compute the quantum noise by deriving the full statistics of the radiated photons out of thermal and/or dynamic equilibrium. The (entanglement) entropy generation is quantified, and the total entropy is shown to be always increasing. Furthermore, we derive a Fokker-Planck equation governing the stochastic angular motion resulting from the fluctuating back-reaction frictional torque. As a result, we find a quantum limit on the uncertainty of the object's angular velocity in steady rotation. Finally, we show in some detail that a rotating object drags nearby objects, making them spin parallel to its axis of rotation. A scalar toy model is introduced in the first part to simplify the technicalities and ease the conceptual complexities; a detailed discussion of quantum electrodynamics is presented in the second part. 1 aMaghrebi, Mohammad, F.1 aJaffe, Robert, L.1 aKardar, Mehran uhttp://arxiv.org/abs/1401.0701v102028nas a2200229 4500008004100000245008700041210006900128260001300197300001400210490000800224520134100232100002101573700001901594700001501613700001901628700001701647700002301664700002501687700002501712700002401737856003701761 2014 eng d00aNon-local propagation of correlations in long-range interacting quantum systems 0 aNonlocal propagation of correlations in longrange interacting qu c2014/7/9 a198 - 2010 v5113 a The maximum speed with which information can propagate in a quantum many-body system directly affects how quickly disparate parts of the system can become correlated and how difficult the system will be to describe numerically. For systems with only short-range interactions, Lieb and Robinson derived a constant-velocity bound that limits correlations to within a linear effective light cone. However, little is known about the propagation speed in systems with long-range interactions, since the best long-range bound is too loose to give the correct light-cone shape for any known spin model and since analytic solutions rarely exist. In this work, we experimentally determine the spatial and time-dependent correlations of a far-from-equilibrium quantum many-body system evolving under a long-range Ising- or XY-model Hamiltonian. For several different interaction ranges, we extract the shape of the light cone and measure the velocity with which correlations propagate through the system. In many cases we find increasing propagation velocities, which violate the Lieb-Robinson prediction, and in one instance cannot be explained by any existing theory. Our results demonstrate that even modestly-sized quantum simulators are well-poised for studying complicated many-body systems that are intractable to classical computation. 1 aRicherme, Philip1 aGong, Zhe-Xuan1 aLee, Aaron1 aSenko, Crystal1 aSmith, Jacob1 aFoss-Feig, Michael1 aMichalakis, Spyridon1 aGorshkov, Alexey, V.1 aMonroe, Christopher uhttp://arxiv.org/abs/1401.5088v101399nas a2200157 4500008004100000245006700041210006600108260001400174490000800188520091600196100001901112700002301131700002501154700002501179856003701204 2014 eng d00aPersistence of locality in systems with power-law interactions0 aPersistence of locality in systems with powerlaw interactions c2014/7/160 v1133 a Motivated by recent experiments with ultra-cold matter, we derive a new bound on the propagation of information in $D$-dimensional lattice models exhibiting $1/r^{\alpha}$ interactions with $\alpha>D$. The bound contains two terms: One accounts for the short-ranged part of the interactions, giving rise to a bounded velocity and reflecting the persistence of locality out to intermediate distances, while the other contributes a power-law decay at longer distances. We demonstrate that these two contributions not only bound but, except at long times, \emph{qualitatively reproduce} the short- and long-distance dynamical behavior following a local quench in an $XY$ chain and a transverse-field Ising chain. In addition to describing dynamics in numerous intractable long-range interacting lattice models, our results can be experimentally verified in a variety of ultracold-atomic and solid-state systems. 1 aGong, Zhe-Xuan1 aFoss-Feig, Michael1 aMichalakis, Spyridon1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1401.6174v200657nas a2200229 4500008004100000245006300041210006200104300000800166490000800174100001400182700002500196700001600221700001700237700001400254700001900268700001300287700001300300700001000313700001600323700001700339856007100356 2014 eng d00aProbing many-body interactions in an optical lattice clock0 aProbing manybody interactions in an optical lattice clock a3110 v3401 aRey, A, M1 aGorshkov, Alexey, V.1 aKraus, C, V1 aMartin, M, J1 aBishof, M1 aSwallows, M, D1 aZhang, X1 aBenko, C1 aYe, J1 aLemke, N, D1 aLudlow, A, D uhttp://www.sciencedirect.com/science/article/pii/S000349161300254601850nas a2200205 4500008004100000245008200041210006900123260001500192490000700207520120600214100002601420700002601446700002301472700002701495700002701522700001701549700002101566700002001587856003701607 2014 eng d00aQuantum correlations and entanglement in far-from-equilibrium spin systems 0 aQuantum correlations and entanglement in farfromequilibrium spin c2014/12/150 v903 a By applying complementary analytic and numerical methods, we investigate the dynamics of spin-$1/2$ XXZ models with variable-range interactions in arbitrary dimensions. The dynamics we consider is initiated from uncorrelated states that are easily prepared in experiments, and can be equivalently viewed as either Ramsey spectroscopy or a quantum quench. Our primary focus is the dynamical emergence of correlations and entanglement in these far-from-equilibrium interacting quantum systems: we characterize these correlations by the entanglement entropy, concurrence, and squeezing, which are inequivalent measures of entanglement corresponding to different quantum resources. In one spatial dimension, we show that the time evolution of correlation functions manifests a non-perturbative dynamic singularity. This singularity is characterized by a universal power-law exponent that is insensitive to small perturbations. Explicit realizations of these models in current experiments using polar molecules, trapped ions, Rydberg atoms, magnetic atoms, and alkaline-earth and alkali atoms in optical lattices, along with the relative merits and limitations of these different systems, are discussed. 1 aHazzard, Kaden, R. A.1 avan den Worm, Mauritz1 aFoss-Feig, Michael1 aManmana, Salvatore, R.1 aTorre, Emanuele, Dalla1 aPfau, Tilman1 aKastner, Michael1 aRey, Ana, Maria uhttp://arxiv.org/abs/1406.0937v101278nas a2200205 4500008004100000245009000041210006900131260001400200490000700214520065300221100001600874700001300890700002000903700002700923700002100950700001800971700002500989700002101014856003701035 2014 eng d00aScattering resonances and bound states for strongly interacting Rydberg polaritons 0 aScattering resonances and bound states for strongly interacting  c2014/11/30 v903 a We provide a theoretical framework describing slow-light polaritons interacting via atomic Rydberg states. We use a diagrammatic method to analytically derive the scattering properties of two polaritons. We identify parameter regimes where polariton-polariton interactions are repulsive. Furthermore, in the regime of attractive interactions, we identify multiple two-polariton bound states, calculate their dispersion, and study the resulting scattering resonances. Finally, the two-particle scattering properties allow us to derive the effective low-energy many-body Hamiltonian. This theoretical platform is applicable to ongoing experiments. 1 aBienias, P.1 aChoi, S.1 aFirstenberg, O.1 aMaghrebi, Mohammad, F.1 aGullans, Michael1 aLukin, M., D.1 aGorshkov, Alexey, V.1 aBüchler, H., P. uhttp://arxiv.org/abs/1402.7333v102020nas a2200265 4500008004100000245009000041210006900131260001400200490000800214520123900222100001501461700001801476700002301494700002801517700001801545700002601563700001201589700002201601700002101623700002101644700001201665700002001677700002001697856003701717 2014 eng d00aSuppressing the loss of ultracold molecules via the continuous quantum Zeno effect 0 aSuppressing the loss of ultracold molecules via the continuous q c2014/2/200 v1123 a We investigate theoretically the suppression of two-body losses when the on-site loss rate is larger than all other energy scales in a lattice. This work quantitatively explains the recently observed suppression of chemical reactions between two rotational states of fermionic KRb molecules confined in one-dimensional tubes with a weak lattice along the tubes [Yan et al., Nature 501, 521-525 (2013)]. New loss rate measurements performed for different lattice parameters but under controlled initial conditions allow us to show that the loss suppression is a consequence of the combined effects of lattice confinement and the continuous quantum Zeno effect. A key finding, relevant for generic strongly reactive systems, is that while a single-band theory can qualitatively describe the data, a quantitative analysis must include multiband effects. Accounting for these effects reduces the inferred molecule filling fraction by a factor of five. A rate equation can describe much of the data, but to properly reproduce the loss dynamics with a fixed filling fraction for all lattice parameters we develop a mean-field model and benchmark it with numerically exact time-dependent density matrix renormalization group calculations. 1 aZhu, Bihui1 aGadway, Bryce1 aFoss-Feig, Michael1 aSchachenmayer, Johannes1 aWall, Michael1 aHazzard, Kaden, R. A.1 aYan, Bo1 aMoses, Steven, A.1 aCovey, Jacob, P.1 aJin, Deborah, S.1 aYe, Jun1 aHolland, Murray1 aRey, Ana, Maria uhttp://arxiv.org/abs/1310.2221v201306nas a2200145 4500008004100000245011100041210006900152260001300221490000700234520073400241100001600975700001800991700002101009856013001030 2014 eng d00aWhen the asymptotic limit offers no advantage in the local-operations-and-classical-communication paradigm0 aWhen the asymptotic limit offers no advantage in the localoperat c5/9/20140 v893 a

We consider bipartite LOCC, the class of operations implementable by local quantum operations and classical communication between two parties. Surprisingly, there are operations that can be approximated to arbitrary precision but are impossible to implement exactly if only a finite number of messages are exchanged. This significantly complicates the analysis of what can or cannot be approximated with LOCC. Toward alleviating this problem, we exhibit two scenarios in which allowing vanishing error does not help. The first scenario is implementation of projective measurements with product measurement operators. The second scenario is the discrimination of unextendable product bases on two three-dimensional systems.

1 aFu, Honghao1 aLeung, Debbie1 aMancinska, Laura uhttps://www.quics.umd.edu/publications/when-asymptotic-limit-offers-no-advantage-local-operations-and-classical-communication01262nas a2200193 4500008004100000245009300041210006900134260001400203490000700217520064800224100002200872700002000894700002500914700002000939700002400959700002100983700002701004856003701031 2013 eng d00aControllable quantum spin glasses with magnetic impurities embedded in quantum solids 0 aControllable quantum spin glasses with magnetic impurities embed c2013/7/240 v883 a Magnetic impurities embedded in inert solids can exhibit long coherence times and interact with one another via their intrinsic anisotropic dipolar interaction. We argue that, as a consequence of these properties, disordered ensembles of magnetic impurities provide an effective platform for realizing a controllable, tunable version of the dipolar quantum spin glass seen in LiHo$_x$Y$_{1-x}$F$_4$. Specifically, we propose and analyze a system composed of dysprosium atoms embedded in solid helium. We describe the phase diagram of the system and discuss the realizability and detectability of the quantum spin glass and antiglass phases. 1 aLemeshko, Mikhail1 aYao, Norman, Y.1 aGorshkov, Alexey, V.1 aWeimer, Hendrik1 aBennett, Steven, D.1 aMomose, Takamasa1 aGopalakrishnan, Sarang uhttp://arxiv.org/abs/1307.1130v101734nas a2200133 4500008004100000245010900041210006900150260001400219490000700233520128500240100001901525700001901544856003701563 2013 eng d00aControlling the group velocity of colliding atomic Bose-Einstein condensates with Feshbach resonances 0 aControlling the group velocity of colliding atomic BoseEinstein  c2013/5/100 v873 a We report on a proposal to change the group velocity of a small Bose Einstein Condensate (BEC) upon collision with another BEC in analogy to slowing of light passing through dispersive media. We make use of ultracold collisions near a magnetic Feshbach resonance, which gives rise to a sharp variation in scattering length with collision energy and thereby changes the group velocity. A generalized Gross-Pitaveskii equation is derived for a small BEC moving through a larger stationary BEC. We denote the two condensates by laser and medium BEC, respectively, to highlight the analogy to a laser pulse travelling through a medium. We derive an expression for the group velocity in a homogeneous medium as well as for the difference in distance, $\delta$, covered by the laser BEC in the presence and absence of a finite-sized medium BEC with a Thomas-Fermi density distribution. For a medium and laser of the same isotopic species, the shift $\delta$ has an upper bound of twice the Thomas-Fermi radius of the medium. For typical narrow Feshbach resonances and a medium with number density $10^{15}$ cm$^{-3}$ up to 85% of the upper bound can be achieved, making the effect experimentally observable. We also derive constraints on the experimental realization of our proposal. 1 aMathew, Ranchu1 aTiesinga, Eite uhttp://arxiv.org/abs/1301.4234v201124nas a2200145 4500008004100000245007500041210006900116260001400185490000800199520068100207100001900888700001800907700001600925856003700941 2013 eng d00aElectrically-protected resonant exchange qubits in triple quantum dots0 aElectricallyprotected resonant exchange qubits in triple quantum c2013/7/310 v1113 aWe present a modulated microwave approach for quantum computing with qubits comprising three spins in a triple quantum dot. This approach includes single- and two-qubit gates that are protected against low-frequency electrical noise, due to an operating point with a narrowband response to high frequency electric fields. Furthermore, existing double quantum dot advances, including robust preparation and measurement via spin-to-charge conversion, are immediately applicable to the new qubit. Finally, the electric dipole terms implicit in the high frequency coupling enable strong coupling with superconducting microwave resonators, leading to more robust two-qubit gates. 1 aTaylor, J., M.1 aSrinivasa, V.1 aMedford, J. uhttp://arxiv.org/abs/1304.3407v201475nas a2200145 4500008004100000022001400041245007300055210006900128260001500197300001200212490000600224520104100230100001701271856004101288 2013 eng d a1551-305X00aEvasiveness of Graph Properties and Topological Fixed-Point Theorems0 aEvasiveness of Graph Properties and Topological FixedPoint Theor c2013/05/16 a337-4150 v73 a

Many graph properties (e.g., connectedness, containing a complete subgraph) are known to be difficult to check. In a decision-tree model, the cost of an algorithm is measured by the number of edges in the graph that it queries. R. Karp conjectured in the early 1970s that all monotone graph properties are evasive -- that is, any algorithm which computes a monotone graph property must check all edges in the worst case. This conjecture is unproven, but a lot of progress has been made. Starting with the work of Kahn, Saks, and Sturtevant in 1984, topological methods have been applied to prove partial results on the Karp conjecture. This text is a tutorial on these topological methods. I give a fully self-contained account of the central proofs from the paper of Kahn, Saks, and Sturtevant, with no prior knowledge of topology assumed. I also briefly survey some of the more recent results on evasiveness.

1 aMiller, Carl uhttp://dx.doi.org/10.1561/040000005501243nas a2200181 4500008004100000245012700041210006900168260001400237490000700251520064800258100002100906700001900927700001700946700001500963700002200978700002401000856003701024 2013 eng d00aExperimental Performance of a Quantum Simulator: Optimizing Adiabatic Evolution and Identifying Many-Body Ground States 0 aExperimental Performance of a Quantum Simulator Optimizing Adiab c2013/7/310 v883 a We use local adiabatic evolution to experimentally create and determine the ground state spin ordering of a fully-connected Ising model with up to 14 spins. Local adiabatic evolution -- in which the system evolution rate is a function of the instantaneous energy gap -- is found to maximize the ground state probability compared with other adiabatic methods while only requiring knowledge of the lowest $\sim N$ of the $2^N$ Hamiltonian eigenvalues. We also demonstrate that the ground state ordering can be experimentally identified as the most probable of all possible spin configurations, even when the evolution is highly non-adiabatic. 1 aRicherme, Philip1 aSenko, Crystal1 aSmith, Jacob1 aLee, Aaron1 aKorenblit, Simcha1 aMonroe, Christopher uhttp://arxiv.org/abs/1305.2253v101291nas a2200157 4500008004100000245007400041210006900115260001400184490000800198520079400206100002601000700002701026700002301053700002001076856003701096 2013 eng d00aFar from equilibrium quantum magnetism with ultracold polar molecules0 aFar from equilibrium quantum magnetism with ultracold polar mole c2013/2/110 v1103 a Recent theory has indicated how to emulate tunable models of quantum magnetism with ultracold polar molecules. Here we show that present molecule optical lattice experiments can accomplish three crucial goals for quantum emulation, despite currently being well below unit filling and not quantum degenerate. The first is to verify and benchmark the models proposed to describe these systems. The second is to prepare correlated and possibly useful states in well-understood regimes. The third is to explore many-body physics inaccessible to existing theoretical techniques. Our proposal relies on a non-equilibrium protocol that can be viewed either as Ramsey spectroscopy or an interaction quench. It uses only routine experimental tools available in any ultracold molecule experiment. 1 aHazzard, Kaden, R. A.1 aManmana, Salvatore, R.1 aFoss-Feig, Michael1 aRey, Ana, Maria uhttp://arxiv.org/abs/1209.4076v101336nas a2200169 4500008004100000245006500041210006300106260001300169300001600182490000800198520084400206100002301050700001801073700002101091700001701112856003701129 2013 eng d00aA framework for bounding nonlocality of state discrimination0 aframework for bounding nonlocality of state discrimination c2013/9/4 a1121 - 11530 v3233 a We consider the class of protocols that can be implemented by local quantum operations and classical communication (LOCC) between two parties. In particular, we focus on the task of discriminating a known set of quantum states by LOCC. Building on the work in the paper "Quantum nonlocality without entanglement" [BDF+99], we provide a framework for bounding the amount of nonlocality in a given set of bipartite quantum states in terms of a lower bound on the probability of error in any LOCC discrimination protocol. We apply our framework to an orthonormal product basis known as the domino states and obtain an alternative and simplified proof that quantifies its nonlocality. We generalize this result for similar bases in larger dimensions, as well as the "rotated" domino states, resolving a long-standing open question [BDF+99]. 1 aChilds, Andrew, M.1 aLeung, Debbie1 aMancinska, Laura1 aOzols, Maris uhttp://arxiv.org/abs/1206.5822v100982nas a2200169 4500008004100000245008200041210006900123260001500192300001100207490000700218520047100225100002300696700001800719700002100737700001700758856003700775 2013 eng d00aInterpolatability distinguishes LOCC from separable von Neumann measurements0 aInterpolatability distinguishes LOCC from separable von Neumann  c2013/06/25 a1122040 v543 a Local operations with classical communication (LOCC) and separable operations are two classes of quantum operations that play key roles in the study of quantum entanglement. Separable operations are strictly more powerful than LOCC, but no simple explanation of this phenomenon is known. We show that, in the case of von Neumann measurements, the ability to interpolate measurements is an operational principle that sets apart LOCC and separable operations. 1 aChilds, Andrew, M.1 aLeung, Debbie1 aMancinska, Laura1 aOzols, Maris uhttp://arxiv.org/abs/1306.5992v103288nas a2200169 4500008004100000245006700041210006500108260001500173300001100188490000700199520278500206100002002991700001703011700001603028700001903044856005503063 2013 eng d00aOptimal entanglement-assisted one-shot classical communication0 aOptimal entanglementassisted oneshot classical communication c2013/06/03 a0623010 v873 a

The one-shot success probability of a noisy classical channel for transmitting one classical bit is the optimal probability with which the bit can be successfully sent via a single use of the channel. Prevedel et al. [Phys. Rev. Lett. 106, 110505 (2011)] recently showed that for a specific channel, this quantity can be increased if the parties using the channel share an entangled quantum state. In this paper, we characterize the optimal entanglement-assisted protocols in terms of the radius of a set of operators associated with the channel. This characterization can be used to construct optimal entanglement-assisted protocols for a given classical channel and to prove the limits of such protocols. As an example, we show that the Prevedel et al. protocol is optimal for two-qubit entanglement. We also prove some tight upper bounds on the improvement that can be obtained from quantum and nonsignaling correlations.

1 aHemenway, Brett1 aMiller, Carl1 aShi, Yaoyun1 aWootters, Mary uhttp://link.aps.org/doi/10.1103/PhysRevA.87.06230101403nas a2200193 4500008004100000245006100041210006000102260007900162300001400241490000700255520072700262653001900989653002501008653002901033653001701062100001701079700001601096856009701112 2013 eng d00aOptimal robust self-testing by binary nonlocal XOR games0 aOptimal robust selftesting by binary nonlocal XOR games bSchloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing a254–2620 v223 a

Self-testing a quantum apparatus means verifying the existence of a certain quantum state as well as the effect of the associated measuring devices based only on the statistics of the measurement outcomes. Robust (i.e., error-tolerant) self-testing quantum apparatuses are critical building blocks for quantum cryptographic protocols that rely on imperfect or untrusted devices. We devise a general scheme for proving optimal robust self-testing properties for tests based on nonlocal binary XOR games. We offer some simplified proofs of known results on self-testing, and also prove some new results.

10anonlocal games10aquantum cryptography10aRandom number generation10aSelf-testing1 aMiller, Carl1 aShi, Yaoyun uhttps://www.quics.umd.edu/publications/optimal-robust-self-testing-binary-nonlocal-xor-games01289nas a2200205 4500008004100000245007500041210006900116260001300185490000800198520067800206100002100884700001900905700002200924700001700946700001500963700001900978700002500997700002401022856003701046 2013 eng d00aQuantum Catalysis of Magnetic Phase Transitions in a Quantum Simulator0 aQuantum Catalysis of Magnetic Phase Transitions in a Quantum Sim c2013/9/50 v1113 a We control quantum fluctuations to create the ground state magnetic phases of a classical Ising model with a tunable longitudinal magnetic field using a system of 6 to 10 atomic ion spins. Due to the long-range Ising interactions, the various ground state spin configurations are separated by multiple first-order phase transitions, which in our zero temperature system cannot be driven by thermal fluctuations. We instead use a transverse magnetic field as a quantum catalyst to observe the first steps of the complete fractal devil's staircase, which emerges in the thermodynamic limit and can be mapped to a large number of many-body and energy-optimization problems. 1 aRicherme, Philip1 aSenko, Crystal1 aKorenblit, Simcha1 aSmith, Jacob1 aLee, Aaron1 aIslam, Rajibul1 aCampbell, Wesley, C.1 aMonroe, Christopher uhttp://arxiv.org/abs/1303.6983v201052nas a2200145 4500008004100000245005700041210005600098260001500154490000700169520062400176100002700800700002300827700001900850856003700869 2013 eng d00aQuantum Cherenkov Radiation and Non-contact Friction0 aQuantum Cherenkov Radiation and Noncontact Friction c2013/10/210 v883 a We present a number of arguments to demonstrate that a quantum analog of Cherenkov effect occurs when two dispersive objects are in relative motion. Specifically we show that two semi-infinite plates experience friction beyond a threshold velocity which, in their center-of-mass frame, is the phase speed of light within their medium. The loss in mechanical energy is radiated away through the plates before getting fully absorbed in the form of heat. By deriving various correlation functions inside and outside the two plates, we explicitly compute the radiation, and discuss its dependence on the reference frame. 1 aMaghrebi, Mohammad, F.1 aGolestanian, Ramin1 aKardar, Mehran uhttp://arxiv.org/abs/1304.4909v200594nas a2200205 4500008004100000245006400041210006100105300000800166490000800174100001700182700001400199700001900213700001300232700001300245700001900258700002500277700001400302700001200316856006000328 2013 eng d00aA quantum many-body spin system in an optical lattice clock0 aquantum manybody spin system in an optical lattice clock a6320 v3411 aMartin, M, J1 aBishof, M1 aSwallows, M, D1 aZhang, X1 aBenko, C1 avon-Stecher, J1 aGorshkov, Alexey, V.1 aRey, A, M1 aYe, Jun uhttp://www.sciencemag.org/content/341/6146/632.abstract01080nas a2200193 4500008004100000245003200041210002800073260001400101490000800115520060900123100001600732700001300748700001900761700001900780700001100799700002000810700001900830856003700849 2013 eng d00aThe Resonant Exchange Qubit0 aResonant Exchange Qubit c2013/7/310 v1113 aWe introduce a solid-state qubit in which exchange interactions among confined electrons provide both the static longitudinal field and the oscillatory transverse field, allowing rapid and full qubit control via rf gate-voltage pulses. We demonstrate two-axis control at a detuning sweet-spot, where leakage due to hyperfine coupling is suppressed by the large exchange gap. A {\pi}/2-gate time of 2.5 ns and a coherence time of 19 {\mu}s, using multi-pulse echo, are also demonstrated. Model calculations that include effects of hyperfine noise are in excellent quantitative agreement with experiment. 1 aMedford, J.1 aBeil, J.1 aTaylor, J., M.1 aRashba, E., I.1 aLu, H.1 aGossard, A., C.1 aMarcus, C., M. uhttp://arxiv.org/abs/1304.3413v201136nas a2200145 4500008004100000245005800041210005600099260001300155490000700168520070900175100002700884700002300911700001900934856003700953 2013 eng d00aA Scattering Approach to the Dynamical Casimir Effect0 aScattering Approach to the Dynamical Casimir Effect c2013/1/70 v873 a We develop a unified scattering approach to dynamical Casimir problems which can be applied to both accelerating boundaries, as well as dispersive objects in relative motion. A general (trace) formula is derived for the radiation from accelerating boundaries. Applications are provided for objects with different shapes in various dimensions, and undergoing rotational or linear motion. Within this framework, photon generation is discussed in the context of a modulated optical mirror. For dispersive objects, we find general results solely in terms of the scattering matrix. Specifically, we discuss the vacuum friction on a rotating object, and the friction on an atom moving parallel to a surface. 1 aMaghrebi, Mohammad, F.1 aGolestanian, Ramin1 aKardar, Mehran uhttp://arxiv.org/abs/1210.1842v201244nas a2200241 4500008004100000245008400041210006900125260001300194300001400207490000600221520055700227100001600784700001300800700001900813700002100832700002000853700001900873700002300892700001100915700002000926700001900946856003700965 2013 eng d00aSelf-Consistent Measurement and State Tomography of an Exchange-Only Spin Qubit0 aSelfConsistent Measurement and State Tomography of an ExchangeOn c2013/9/1 a654 - 6590 v83 aWe report initialization, complete electrical control, and single-shot readout of an exchange-only spin qubit. Full control via the exchange interaction is fast, yielding a demonstrated 75 qubit rotations in under 2 ns. Measurement and state tomography are performed using a maximum-likelihood estimator method, allowing decoherence, leakage out of the qubit state space, and measurement fidelity to be quantified. The methods developed here are generally applicable to systems with state leakage, noisy measurements, and non-orthogonal control axes. 1 aMedford, J.1 aBeil, J.1 aTaylor, J., M.1 aBartlett, S., D.1 aDoherty, A., C.1 aRashba, E., I.1 aDiVincenzo, D., P.1 aLu, H.1 aGossard, A., C.1 aMarcus, C., M. uhttp://arxiv.org/abs/1302.1933v100867nas a2200145 4500008004100000245007400041210006900115260001500184520040100199100002300600700002000623700001900643700002200662856003700684 2013 eng d00aA Time-Efficient Quantum Walk for 3-Distinctness Using Nested Updates0 aTimeEfficient Quantum Walk for 3Distinctness Using Nested Update c2013/02/283 a We present an extension to the quantum walk search framework that facilitates quantum walks with nested updates. We apply it to give a quantum walk algorithm for 3-Distinctness with query complexity ~O(n^{5/7}), matching the best known upper bound (obtained via learning graphs) up to log factors. Furthermore, our algorithm has time complexity ~O(n^{5/7}), improving the previous ~O(n^{3/4}). 1 aChilds, Andrew, M.1 aJeffery, Stacey1 aKothari, Robin1 aMagniez, Frederic uhttp://arxiv.org/abs/1302.7316v101446nas a2200169 4500008004100000245006700041210006600108260001400174490000700188520092200195100002701117700002401144700002601168700002001194700002501214856003701239 2013 eng d00aTopological phases in ultracold polar-molecule quantum magnets0 aTopological phases in ultracold polarmolecule quantum magnets c2013/2/260 v873 a We show how to use polar molecules in an optical lattice to engineer quantum spin models with arbitrary spin S >= 1/2 and with interactions featuring a direction-dependent spin anisotropy. This is achieved by encoding the effective spin degrees of freedom in microwave-dressed rotational states of the molecules and by coupling the spins through dipolar interactions. We demonstrate how one of the experimentally most accessible anisotropies stabilizes symmetry protected topological phases in spin ladders. Using the numerically exact density matrix renormalization group method, we find that these interacting phases -- previously studied only in the nearest-neighbor case -- survive in the presence of long-range dipolar interactions. We also show how to use our approach to realize the bilinear-biquadratic spin-1 and the Kitaev honeycomb models. Experimental detection schemes and imperfections are discussed. 1 aManmana, Salvatore, R.1 aStoudenmire, E., M.1 aHazzard, Kaden, R. A.1 aRey, Ana, Maria1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1210.5518v201302nas a2200145 4500008004100000245008300041210006900124260001500193300001200208490000900220520081500229100001901044700001901063856007401082 2012 eng d00aFull Abstraction for Set-Based Models of the Symmetric Interaction Combinators0 aFull Abstraction for SetBased Models of the Symmetric Interactio c2012/01/01 a316-3300 v72133 aThe symmetric interaction combinators are a model of distributed and deterministic computation based on Lafont’s interaction nets, a special form of graph rewriting. The interest of the symmetric interaction combinators lies in their universality, that is, the fact that they may encode all other interaction net systems; for instance, several implementations of the lambda-calculus in the symmetric interaction combinators exist, related to Lamping’s sharing graphs for optimal reduction. A certain number of observational equivalences were introduced for this system, by Lafont, Fernandez and Mackie, and the first author. In this paper, we study the problem of full abstraction with respect to one of these equivalences, using a class of very simple denotational models based on pointed sets.1 aMazza, Damiano1 aRoss, Neil, J. uhttps://lipn.univ-paris13.fr/~mazza/papers/CombSetSem-FOSSACS2012.pdf01519nas a2200217 4500008004100000245008300041210006900124260001400193490000800207520087700215100002001092700002101112700002201133700001201155700002101167700002301188700002001211700002101231700001201252856003701264 2012 eng d00aLong-lived dipolar molecules and Feshbach molecules in a 3D optical lattice 0 aLonglived dipolar molecules and Feshbach molecules in a 3D optic c2012/2/230 v1083 a We have realized long-lived ground-state polar molecules in a 3D optical lattice, with a lifetime of up to 25 s, which is limited only by off-resonant scattering of the trapping light. Starting from a 2D optical lattice, we observe that the lifetime increases dramatically as a small lattice potential is added along the tube-shaped lattice traps. The 3D optical lattice also dramatically increases the lifetime for weakly bound Feshbach molecules. For a pure gas of Feshbach molecules, we observe a lifetime of >20 s in a 3D optical lattice; this represents a 100-fold improvement over previous results. This lifetime is also limited by off-resonant scattering, the rate of which is related to the size of the Feshbach molecule. Individually trapped Feshbach molecules in the 3D lattice can be converted to pairs of K and Rb atoms and back with nearly 100% efficiency. 1 aChotia, Amodsen1 aNeyenhuis, Brian1 aMoses, Steven, A.1 aYan, Bo1 aCovey, Jacob, P.1 aFoss-Feig, Michael1 aRey, Ana, Maria1 aJin, Deborah, S.1 aYe, Jun uhttp://arxiv.org/abs/1110.4420v101592nas a2200205 4500008004100000245012500041210006900166260001500235520091800250100001801168700002001186700002601206700002001232700001901252700001901271700001801290700002101308700002001329856003701349 2012 eng d00aPhotonic quantum simulation of ground state configurations of Heisenberg square and checkerboard lattice spin systems 0 aPhotonic quantum simulation of ground state configurations of He c2012/05/123 a Photonic quantum simulators are promising candidates for providing insight into other small- to medium-sized quantum systems. The available photonic quantum technology is reaching the state where significant advantages arise for the quantum simulation of interesting questions in Heisenberg spin systems. Here we experimentally simulate such spin systems with single photons and linear optics. The effective Heisenberg-type interactions among individual single photons are realized by quantum interference at the tunable direction coupler followed by the measurement process. The effective interactions are characterized by comparing the entanglement dynamics using pairwise concurrence of a four-photon quantum system. We further show that photonic quantum simulations of generalized Heisenberg interactions on a four-site square lattice and a six-site checkerboard lattice are in reach of current technology. 1 aMa, Xiao-song1 aDakic, Borivoje1 aKropatsche, Sebastian1 aNaylor, William1 aChan, Yang-hao1 aGong, Zhe-Xuan1 aDuan, Lu-ming1 aZeilinger, Anton1 aWalther, Philip uhttp://arxiv.org/abs/1205.2801v101667nas a2200145 4500008004100000245006400041210006200105260001400167490000700181520123200188100002701420700001801447700001901465856003701484 2012 eng d00aPolymer-mediated entropic forces between scale-free objects0 aPolymermediated entropic forces between scalefree objects c2012/12/30 v863 a The number of configurations of a polymer is reduced in the presence of a barrier or an obstacle. The resulting loss of entropy adds a repulsive component to other forces generated by interaction potentials. When the obstructions are scale invariant shapes (such as cones, wedges, lines or planes) the only relevant length scales are the polymer size R_0 and characteristic separations, severely constraining the functional form of entropic forces. Specifically, we consider a polymer (single strand or star) attached to the tip of a cone, at a separation h from a surface (or another cone). At close proximity, such that h<In this brief report, we consider the equivalence between two sets of m + 1 bipartite quantum states under local unitary transformations. For pure states, this problem corresponds to the matrix algebra question of whether two degree m matrix polynomials are unitarily equivalent; i.e. UAiV† = Bi for 0 ≤ i ≤ m where U and V are unitary and (Ai, Bi) are arbitrary pairs of rectangular matrices. We present a randomized polynomial-time algorithm that solves this problem with an arbitrarily high success probability and outputs transforming matrices U and V.

10amatrix polynomials10aSchwartz-Zippel lemma10aunitary transformations1 aChitambar, Eric1 aMiller, Carl1 aShi, Yaoyun uhttp://dl.acm.org/citation.cfm?id=2230936.223094201241nas a2200181 4500008004100000245007500041210006900116260001500185490000700200520070200207100001300909700001500922700001900937700002000956700002300976700002300999856003701022 2011 eng d00aDetecting paired and counterflow superfluidity via dipole oscillations0 aDetecting paired and counterflow superfluidity via dipole oscill c2011/10/270 v843 a We suggest an experimentally feasible procedure to observe paired and counterflow superfluidity in ultra-cold atom systems. We study the time evolution of one-dimensional mixtures of bosonic atoms in an optical lattice following an abrupt displacement of an additional weak confining potential. We find that the dynamic responses of the paired superfluid phase for attractive inter-species interactions and the counterflow superfluid phase for repulsive interactions are qualitatively distinct and reflect the quasi long-range order that characterizes these states. These findings suggest a clear experimental procedure to detect these phases, and give an intuitive insight into their dynamics. 1 aHu, Anzi1 aMathey, L.1 aTiesinga, Eite1 aDanshita, Ippei1 aWilliams, Carl, J.1 aClark, Charles, W. uhttp://arxiv.org/abs/1103.3513v301130nas a2200121 4500008004100000245010300041210006900144260001300213490000700226520071100233100002700944856003700971 2011 eng d00aA diagrammatic expansion of the Casimir energy in multiple reflections: theory and applications 0 adiagrammatic expansion of the Casimir energy in multiple reflect c2011/2/20 v833 a We develop a diagrammatic representation of the Casimir energy of a multibody configuration. The diagrams represent multiple reflections between the objects and can be organized by a few simple rules. The lowest-order diagrams (or reflections) give the main contribution to the Casimir interaction which proves the usefulness of this expansion. Among some applications of this, we find analytical formulae describing the interaction between "edges", i.e. semi-infinite plates, where we also give a first example of blocking in the context of the Casimir energy. We also find the interaction of edges with a needle and describe analytically a recent model of the repulsion due to the Casimir interaction. 1 aMaghrebi, Mohammad, F. uhttp://arxiv.org/abs/1012.1060v101007nas a2200145 4500008004100000245006100041210006000102260001500162300001000177490000700187520058600194100002700780700001700807856003700824 2011 eng d00aElectromagnetic Casimir Energies of Semi-Infinite Planes0 aElectromagnetic Casimir Energies of SemiInfinite Planes c2011/07/01 a140010 v953 a Using recently developed techniques based on scattering theory, we find the electromagnetic Casimir energy for geometries involving semi-infinite planes, a case that is of particular interest in the design of microelectromechanical devices. We obtain both approximate analytic formulae and exact results requiring only modest numerical computation. Using these results, we analyze the effects of edges and orientation on the Casimir energy. We also demonstrate the accuracy, simplicity, and utility of our approximation scheme, which is based on a multiple reflection expansion. 1 aMaghrebi, Mohammad, F.1 aGraham, Noah uhttp://arxiv.org/abs/1102.1486v101014nas a2200157 4500008004100000245004500041210004500086260001500131300001000146490000700156520059200163100002700755700001800782700001900800856003700819 2011 eng d00aEntropic force of polymers on a cone tip0 aEntropic force of polymers on a cone tip c2011/12/01 a660020 v963 a We consider polymers attached to the tip of a cone, and the resulting force due to entropy loss on approaching a plate (or another cone). At separations shorter than the polymer radius of gyration R_g, the only relevant length scale is the tip-plate (or tip-tip) separation h, and the entropic force is given by F=A kT/h. The universal amplitude A can be related to (geometry dependent) correlation exponents of long polymers. We compute A for phantom polymers, and for self-avoiding (including star) polymers by epsilon-expansion, as well as by numerical simulations in 3 dimensions. 1 aMaghrebi, Mohammad, F.1 aKantor, Yacov1 aKardar, Mehran uhttp://arxiv.org/abs/1109.5658v201106nas a2200145 4500008004100000245006700041210006700108260001300175490000700188520065800195100002700853700002100880700002200901856003700923 2011 eng d00aImplications of the Babinet Principle for Casimir Interactions0 aImplications of the Babinet Principle for Casimir Interactions c2011/9/10 v843 a We formulate the Babinet Principle (BP) as a relation between the scattering amplitudes for electromagnetic waves, and combine it with multiple scattering techniques to derive new properties of Casimir forces. We show that the Casimir force exerted by a planar conductor or dielectric on a self- complementary perforated planar mirror is approximately half that on a uniform mirror independent of the distance between them. The BP suggests that Casimir edge effects are anomalously small, supporting results obtained earlier in special cases. Finally, we illustrate how the BP can be used to estimate Casimir forces between perforated planar mirrors. 1 aMaghrebi, Mohammad, F.1 aAbravanel, Ronen1 aJaffe, Robert, L. uhttp://arxiv.org/abs/1103.5395v101053nas a2200157 4500008004100000245008200041210006900123260001500192490000800207520056400215100001900779700002200798700001900820700001900839856003700858 2011 eng d00aLaser cooling and optical detection of excitations in a LC electrical circuit0 aLaser cooling and optical detection of excitations in a LC elect c2011/12/270 v1073 aWe explore a method for laser cooling and optical detection of excitations in a LC electrical circuit. Our approach uses a nanomechanical oscillator as a transducer between optical and electronic excitations. An experimentally feasible system with the oscillator capacitively coupled to the LC and at the same time interacting with light via an optomechanical force is shown to provide strong electro-mechanical coupling. Conditions for improved sensitivity and quantum limited readout of electrical signals with such an "optical loud speaker" are outlined. 1 aTaylor, J., M.1 aSørensen, A., S.1 aMarcus, C., M.1 aPolzik, E., S. uhttp://arxiv.org/abs/1108.2035v101573nas a2200181 4500008004100000245004700041210004700088260001400135490000700149520106900156100002501225700002701250700001501277700001901292700002301311700002001334856003701354 2011 eng d00aQuantum Magnetism with Polar Alkali Dimers0 aQuantum Magnetism with Polar Alkali Dimers c2011/9/150 v843 a We show that dipolar interactions between ultracold polar alkali dimers in optical lattices can be used to realize a highly tunable generalization of the t-J model, which we refer to as the t-J-V-W model. The model features long-range spin-spin interactions J_z and J_perp of XXZ type, long-range density-density interaction V, and long-range density-spin interaction W, all of which can be controlled in both magnitude and sign independently of each other and of the tunneling t. The "spin" is encoded in the rotational degree of freedom of the molecules, while the interactions are controlled by applied static electric and continuous-wave microwave fields. Furthermore, we show that nuclear spins of the molecules can be used to implement an additional (orbital) degree of freedom that is coupled to the original rotational degree of freedom in a tunable way. The presented system is expected to exhibit exotic physics and to provide insights into strongly correlated phenomena in condensed matter systems. Realistic experimental imperfections are discussed. 1 aGorshkov, Alexey, V.1 aManmana, Salvatore, R.1 aChen, Gang1 aDemler, Eugene1 aLukin, Mikhail, D.1 aRey, Ana, Maria uhttp://arxiv.org/abs/1106.1655v100483nas a2200169 4500008004100000245005300041210005200094300001100146490000700157100002500164700001800189700001200207700001400219700001600233700001400249856005000263 2011 eng d00aQuantum magnetism with polar alkali-metal dimers0 aQuantum magnetism with polar alkalimetal dimers a0336190 v841 aGorshkov, Alexey, V.1 aManmana, S, R1 aChen, G1 aDemler, E1 aLukin, M, D1 aRey, A, M uhttp://link.aps.org/abstract/PRA/v84/e033619/01279nas a2200181 4500008004100000245009100041210006900132260001400201490000700215520071200222100002000934700002000954700001900974700002500993700002301018700001901041856003701060 2011 eng d00aSpatial separation in a thermal mixture of ultracold $^{174}$Yb and $^{87}$Rb atoms 0 aSpatial separation in a thermal mixture of ultracold 174 Yb and  c2011/4/210 v833 a We report on the observation of unusually strong interactions in a thermal mixture of ultracold atoms which cause a significant modification of the spatial distribution. A mixture of $^{87}$Rb and $^{174}$Yb with a temperature of a few $\mu$K is prepared in a hybrid trap consisting of a bichromatic optical potential superimposed on a magnetic trap. For suitable trap parameters and temperatures, a spatial separation of the two species is observed. We infer that the separation is driven by a large interaction strength between $^{174}$Yb and $^{87}$Rb accompanied by a large three-body recombination rate. Based on this assumption we have developed a diffusion model which reproduces our observations. 1 aBaumer, Florian1 aMünchow, Frank1 aGörlitz, Axel1 aMaxwell, Stephen, E.1 aJulienne, Paul, S.1 aTiesinga, Eite uhttp://arxiv.org/abs/1104.1722v101551nas a2200193 4500008004100000245008200041210006900123260001300192490000800205520096600213100002501179700002701204700001501231700001201246700001901258700002301277700002001300856003701320 2011 eng d00aTunable Superfluidity and Quantum Magnetism with Ultracold Polar Molecules 0 aTunable Superfluidity and Quantum Magnetism with Ultracold Polar c2011/9/80 v1073 a By selecting two dressed rotational states of ultracold polar molecules in an optical lattice, we obtain a highly tunable generalization of the t-J model, which we refer to as the t-J-V-W model. In addition to XXZ spin exchange, the model features density-density interactions and novel density-spin interactions; all interactions are dipolar. We show that full control of all interaction parameters in both magnitude and sign can be achieved independently of each other and of the tunneling. As a first step towards demonstrating the potential of the system, we apply the density matrix renormalization group method (DMRG) to obtain the 1D phase diagram of the simplest experimentally realizable case. Specifically, we show that the tunability and the long-range nature of the interactions in the t-J-V-W model enable enhanced superfluidity. Finally, we show that Bloch oscillations in a tilted lattice can be used to probe the phase diagram experimentally. 1 aGorshkov, Alexey, V.1 aManmana, Salvatore, R.1 aChen, Gang1 aYe, Jun1 aDemler, Eugene1 aLukin, Mikhail, D.1 aRey, Ana, Maria uhttp://arxiv.org/abs/1106.1644v101458nas a2200145 4500008004100000245005700041210005600098260001500154520102700169100002301196700001801219700002101237700001701258856003701275 2010 eng d00aCharacterization of universal two-qubit Hamiltonians0 aCharacterization of universal twoqubit Hamiltonians c2010/04/093 a Suppose we can apply a given 2-qubit Hamiltonian H to any (ordered) pair of qubits. We say H is n-universal if it can be used to approximate any unitary operation on n qubits. While it is well known that almost any 2-qubit Hamiltonian is 2-universal (Deutsch, Barenco, Ekert 1995; Lloyd 1995), an explicit characterization of the set of non-universal 2-qubit Hamiltonians has been elusive. Our main result is a complete characterization of 2-non-universal 2-qubit Hamiltonians. In particular, there are three ways that a 2-qubit Hamiltonian H can fail to be universal: (1) H shares an eigenvector with the gate that swaps two qubits, (2) H acts on the two qubits independently (in any of a certain family of bases), or (3) H has zero trace. A 2-non-universal 2-qubit Hamiltonian can still be n-universal for some n >= 3. We give some partial results on 3-universality. Finally, we also show how our characterization of 2-universal Hamiltonians implies the well-known result that almost any 2-qubit unitary is universal. 1 aChilds, Andrew, M.1 aLeung, Debbie1 aMancinska, Laura1 aOzols, Maris uhttp://arxiv.org/abs/1004.1645v200869nas a2200133 4500008004100000245005100041210004200092260001500134520048400149100002400633700002000657700002100677856003700698 2010 eng d00aOn the degeneracy of SU(3)k topological phases0 adegeneracy of SU3k topological phases c2010/09/013 a

The ground state degeneracy of an $SU(N)_k$ topological phase with $n$ quasiparticle excitations is relevant quantity for quantum computation, condensed matter physics, and knot theory. It is an open question to find a closed formula for this degeneracy for any $N > 2$. Here we present the problem in an explicit combinatorial way and analyze the case N=3. While not finding a complete closed-form solution, we obtain generating functions and solve some special cases.

1 aJordan, Stephen, P.1 aMansour, Toufik1 aSeverini, Simone uhttp://arxiv.org/abs/1009.0114v101401nas a2200217 4500008004100000245005600041210005600097260001300153490000800166520081300174100002100987700001801008700001901026700001401045700002101059700001901080700001401099700001501113700001801128856003701146 2010 eng d00aDynamic Nuclear Polarization in Double Quantum Dots0 aDynamic Nuclear Polarization in Double Quantum Dots c2010/6/40 v1043 aWe theoretically investigate the controlled dynamic polarization of lattice nuclear spins in GaAs double quantum dots containing two electrons. Three regimes of long-term dynamics are identified, including the build up of a large difference in the Overhauser fields across the dots, the saturation of the nuclear polarization process associated with formation of so-called "dark states," and the elimination of the difference field. We show that in the case of unequal dots, build up of difference fields generally accompanies the nuclear polarization process, whereas for nearly identical dots, build up of difference fields competes with polarization saturation in dark states. The elimination of the difference field does not, in general, correspond to a stable steady state of the polarization process. 1 aGullans, Michael1 aKrich, J., J.1 aTaylor, J., M.1 aBluhm, H.1 aHalperin, B., I.1 aMarcus, C., M.1 aStopa, M.1 aYacoby, A.1 aLukin, M., D. uhttp://arxiv.org/abs/1003.4508v207538nas a2200145 4500008004100000022001400041245006900055210006600124260001500190300001200205490000600217520708300223100001707306856006907323 2010 eng d a1937-065200aAn Euler–Poincaré bound for equicharacteristic étale sheaves0 aEuler–Poincaré bound for equicharacteristic étale sheaves c2010/01/14 a21 - 450 v43 a

The Grothendieck–Ogg–Shafarevich formula expresses the Euler characteristic of an étale sheaf on a characteristic-p curve in terms of local data. The purpose of this paper is to prove an equicharacteristic version of this formula (a bound, rather than an equality). This follows work of R. Pink.

The basis for the proof of this result is the characteristic-p Riemann–Hilbert correspondence, which is a functorial relationship between two different types of sheaves on a characteristic-p scheme. In the paper we prove a one-dimensional version of this correspondence, considering both local and global settings.

1 aMiller, Carl uhttp://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.648.358400782nas a2200265 4500008004100000245009300041210006900134300000800203490000600211100001700217700001500234700001800249700001300267700002500280700001700305700001300322700001700335700001700352700001400369700001600383700001500399700002000414700001600434856006600450 2010 eng d00aFar-field optical imaging and manipulation of individual spins with nanoscale resolution0 aFarfield optical imaging and manipulation of individual spins wi a9120 v61 aMaurer, P, C1 aMaze, J, R1 aStanwix, P, L1 aJiang, L1 aGorshkov, Alexey, V.1 aZibrov, A, A1 aHarke, B1 aHodges, J, S1 aZibrov, A, S1 aYacoby, A1 aTwitchen, D1 aHell, S, W1 aWalsworth, R, L1 aLukin, M, D uhttp://www.nature.com/nphys/journal/v6/n11/abs/nphys1774.html08283nas a2200169 4500008004100000022001300041245005100054210005100105260001500156300001100171490000700182520779500189100002007984700001708004700001608021856007608037 2010 eng d a0022248800aMatrix pencils and entanglement classification0 aMatrix pencils and entanglement classification c2010/01/01 a0722050 v513 a

Quantum entanglement plays a central role in quantum information processing. A main objective of the theory is to classify different types of entanglement according to their interconvertibility through manipulations that do not require additional entanglement to perform. While bipartite entanglement is well understood in this framework, the classification of entanglements among three or more subsystems is inherently much more difficult. In this paper, we study pure state entanglement in systems of dimension 2mn. Two states are considered equivalent if they can be reversibly converted from one to the other with a nonzero probability using only local quantum resources and classical communication (SLOCC). We introduce a connection between entanglement manipulations in these systems and the well-studied theory of matrix pencils. All previous attempts to study general SLOCC equivalence in such systems have relied on somewhat contrived techniques which fail to reveal the elegant structure of the problem that can be seen from the matrix pencil approach. Based on this method, we report the first polynomial-time algorithm for deciding when two2mstates are SLOCC equivalent. We then proceed to present a canonical form for all 2mstates based on the matrix pencil construction such that two states are equivalent if and only if they have the same canonical form. Besides recovering the previously known 26 distinct SLOCC equivalence classes in 23systems, we also determine the hierarchy between these classes.

1 aChitambar, Eric1 aMiller, Carl1 aShi, Yaoyun uhttp://scitation.aip.org/content/aip/journal/jmp/51/7/10.1063/1.345906901378nas a2200157 4500008004100000245007600041210006900117260001300186490000700199520090300206100001301109700001501122700002301137700002301160856003701183 2010 eng d00aNoise correlations of one-dimensional Bose mixtures in optical lattices0 aNoise correlations of onedimensional Bose mixtures in optical la c2010/6/20 v813 a We study the noise correlations of one-dimensional binary Bose mixtures, as a probe of their quantum phases. In previous work, we found a rich structure of many-body phases in such mixtures, such as paired and counterflow superfluidity. Here we investigate the signature of these phases in the noise correlations of the atomic cloud after time-of-flight expansion, using both Luttinger liquid theory and the time-evolving block decimation (TEBD) method. We find that paired and counterflow superfluidity exhibit distinctive features in the noise spectra. We treat both extended and inhomogeneous systems, and our numerical work shows that the essential physics of the extended systems is present in the trapped-atom systems of current experimental interest. For paired and counterflow superfluid phases, we suggest methods for extracting Luttinger parameters from noise correlation spectroscopy. 1 aHu, Anzi1 aMathey, L.1 aWilliams, Carl, J.1 aClark, Charles, W. uhttp://arxiv.org/abs/1002.4918v202230nas a2200133 4500008004100000245006800041210006600109490000600175520174200181100001901923700002201942700002301964856010901987 2010 eng d00aQuantum Algorithms for Simon’s Problem over Nonabelian Groups0 aQuantum Algorithms for Simon s Problem over Nonabelian Groups0 v63 a

Daniel Simon's 1994 discovery of an efficient quantum algorithm for finding “hidden shifts” of Z2n provided the first algebraic problem for which quantum computers are exponentially faster than their classical counterparts. In this article, we study the generalization of Simon's problem to arbitrary groups. Fixing a finite group G, this is the problem of recovering an involution m = (m1,…,mn) ∈ Gn from an oracle f with the property that f(x ⋅ y) = f(x) ⇔ y ∈ {1, m}. In the current parlance, this is the hidden subgroup problem (HSP) over groups of the form Gn, where G is a nonabelian group of constant size, and where the hidden subgroup is either trivial or has order two.

Although groups of the form Gn have a simple product structure, they share important representation--theoretic properties with the symmetric groups Sn, where a solution to the HSP would yield a quantum algorithm for Graph Isomorphism. In particular, solving their HSP with the so-called “standard method” requires highly entangled measurements on the tensor product of many coset states.

In this article, we provide quantum algorithms with time complexity 2O(√n) that recover hidden involutions m = (m1,…mn) ∈ Gn where, as in Simon's problem, each mi is either the identity or the conjugate of a known element m which satisfies κ(m) = −κ(1) for some κ ∈ Ĝ. Our approach combines the general idea behind Kuperberg's sieve for dihedral groups with the “missing harmonic” approach of Moore and Russell. These are the first nontrivial HSP algorithms for group families that require highly entangled multiregister Fourier sampling.

1 aAlagic, Gorjan1 aMoore, Cristopher1 aRussell, Alexander uhttps://www.quics.umd.edu/publications/quantum-algorithms-simon%E2%80%99s-problem-over-nonabelian-groups02052nas a2200193 4500008004100000245002200041210002200063260001300085300001200098490000800110520156800118100002301686700001901709700002201728700002301750700002401773700002401797856003701821 2010 eng d00aQuantum Computing0 aQuantum Computing c2010/3/4 a45 - 530 v4643 a Quantum mechanics---the theory describing the fundamental workings of nature---is famously counterintuitive: it predicts that a particle can be in two places at the same time, and that two remote particles can be inextricably and instantaneously linked. These predictions have been the topic of intense metaphysical debate ever since the theory's inception early last century. However, supreme predictive power combined with direct experimental observation of some of these unusual phenomena leave little doubt as to its fundamental correctness. In fact, without quantum mechanics we could not explain the workings of a laser, nor indeed how a fridge magnet operates. Over the last several decades quantum information science has emerged to seek answers to the question: can we gain some advantage by storing, transmitting and processing information encoded in systems that exhibit these unique quantum properties? Today it is understood that the answer is yes. Many research groups around the world are working towards one of the most ambitious goals humankind has ever embarked upon: a quantum computer that promises to exponentially improve computational power for particular tasks. A number of physical systems, spanning much of modern physics, are being developed for this task---ranging from single particles of light to superconducting circuits---and it is not yet clear which, if any, will ultimately prove successful. Here we describe the latest developments for each of the leading approaches and explain what the major challenges are for the future. 1 aLadd, Thaddeus, D.1 aJelezko, Fedor1 aLaflamme, Raymond1 aNakamura, Yasunobu1 aMonroe, Christopher1 aO'Brien, Jeremy, L. uhttp://arxiv.org/abs/1009.2267v101137nas a2200157 4500008004100000245008200041210006900123260001300192490000700205520065000212100001500862700001900877700002300896700002300919856003700942 2009 eng d00aCollisional cooling of ultra-cold atom ensembles using Feshbach resonances 0 aCollisional cooling of ultracold atom ensembles using Feshbach r c2009/9/80 v803 a We propose a new type of cooling mechanism for ultra-cold fermionic atom ensembles, which capitalizes on the energy dependence of inelastic collisions in the presence of a Feshbach resonance. We first discuss the case of a single magnetic resonance, and find that the final temperature and the cooling rate is limited by the width of the resonance. A concrete example, based on a p-wave resonance of $^{40}$K, is given. We then improve upon this setup by using both a very sharp optical or radio-frequency induced resonance and a very broad magnetic resonance and show that one can improve upon temperatures reached with current technologies. 1 aMathey, L.1 aTiesinga, Eite1 aJulienne, Paul, S.1 aClark, Charles, W. uhttp://arxiv.org/abs/0903.2568v101819nas a2200181 4500008004100000245009700041210006900138260001400207490000700221520125900228100001301487700001501500700002001515700001901535700002301554700002301577856003701600 2009 eng d00aCounterflow and paired superfluidity in one-dimensional Bose mixtures in optical lattices 0 aCounterflow and paired superfluidity in onedimensional Bose mixt c2009/8/240 v803 a We study the quantum phases of mixtures of ultra-cold bosonic atoms held in an optical lattice that confines motion or hopping to one spatial dimension. The phases are found by using Tomonaga-Luttinger liquid theory as well as the numerical method of time evolving block decimation (TEBD). We consider a binary mixture with repulsive intra-species interactions, and either repulsive or attractive inter-species interaction. For a homogeneous system, we find paired- and counterflow-superfluid phases at different filling and hopping energies. We also predict parameter regions in which these types of superfluid order coexist with charge density wave order. We show that the Tomonaga-Luttinger liquid theory and TEBD qualitatively agree on the location of the phase boundary to superfluidity. We then describe how these phases are modified and can be detected when an additional harmonic trap is present. In particular, we show how experimentally measurable quantities, such as time-of-flight images and the structure factor, can be used to distinguish the quantum phases. Finally, we suggest applying a Feshbach ramp to detect the paired superfluid state, and a $\pi/2$ pulse followed by Bragg spectroscopy to detect the counterflow superfluid phase. 1 aHu, Anzi1 aMathey, L.1 aDanshita, Ippei1 aTiesinga, Eite1 aWilliams, Carl, J.1 aClark, Charles, W. uhttp://arxiv.org/abs/0906.2150v101306nas a2200181 4500008004100000245007600041210006900117260001300186490000800199520075700207100001700964700001900981700002501000700002401025700001901049700001901068856003701087 2009 eng d00aNumber Fluctuations and Energy Dissipation in Sodium Spinor Condensates0 aNumber Fluctuations and Energy Dissipation in Sodium Spinor Cond c2009/6/50 v1023 a We characterize fluctuations in atom number and spin populations in F=1 sodium spinor condensates. We find that the fluctuations enable a quantitative measure of energy dissipation in the condensate. The time evolution of the population fluctuations shows a maximum. We interpret this as evidence of a dissipation-driven separatrix crossing in phase space. For a given initial state, the critical time to the separatrix crossing is found to depend exponentially on the magnetic field and linearly on condensate density. This crossing is confirmed by tracking the energy of the spinor condensate as well as by Faraday rotation spectroscopy. We also introduce a phenomenological model that describes the observed dissipation with a single coefficient. 1 aLiu, Yingmei1 aGomez, Eduardo1 aMaxwell, Stephen, E.1 aTurner, Lincoln, D.1 aTiesinga, Eite1 aLett, Paul, D. uhttp://arxiv.org/abs/0906.2110v101474nas a2200133 4500008004100000245009500041210006900136260001500205490000700220520103800227100001401265700002401279856003701303 2009 eng d00aProtocol for Hybrid Entanglement Between a Trapped Atom and a Semiconductor Quantum Dot 0 aProtocol for Hybrid Entanglement Between a Trapped Atom and a Se c2009/12/300 v803 a We propose a quantum optical interface between an atomic and solid state system. We show that quantum states in a single trapped atom can be entangled with the states of a semiconductor quantum dot through their common interaction with a classical laser field. The interference and detection of the resulting scattered photons can then herald the entanglement of the disparate atomic and solid-state quantum bits. We develop a protocol that can succeed despite a significant mismatch in the radiative characteristics of the two matter-based qubits. We study in detail a particular case of this interface applied to a single trapped \Yb ion and a cavity-coupled InGaAs semiconductor quantum dot. Entanglement fidelity and success rates are found to be robust to a broad range of experimental nonideal effects such as dispersion mismatch, atom recoil, and multi-photon scattering. We conclude that it should be possible to produce highly entangled states of these complementary qubit systems under realistic experimental conditions. 1 aWaks, Edo1 aMonroe, Christopher uhttp://arxiv.org/abs/0907.0444v101274nas a2200181 4500008004100000245011400041210006900155260001400224490000800238520068400246100001700930700002000947700002500967700002400992700001901016700002001035856003701055 2009 eng d00aQuantum Phase Transitions and Continuous Observation of Spinor Dynamics in an Antiferromagnetic Condensate 0 aQuantum Phase Transitions and Continuous Observation of Spinor D c2009/3/230 v1023 a Condensates of spin-1 sodium display rich spin dynamics due to the antiferromagnetic nature of the interactions in this system. We use Faraday rotation spectroscopy to make a continuous and minimally destructive measurement of the dynamics over multiple spin oscillations on a single evolving condensate. This method provides a sharp signature to locate a magnetically tuned separatrix in phase space which depends on the net magnetization. We also observe a phase transition from a two- to a three-component condensate at a low but finite temperature using a Stern-Gerlach imaging technique. This transition should be preserved as a zero-temperature quantum phase transition. 1 aLiu, Yingmei1 aJung, Sebastian1 aMaxwell, Stephen, E.1 aTurner, Lincoln, D.1 aTiesinga, Eite1 aLett, Paul., D. uhttp://arxiv.org/abs/0902.3189v101777nas a2200241 4500008004100000245007500041210006900116260001400185490000700199520107300206100001801279700002701297700001801324700001901342700001701361700002101378700001901399700002101418700002001439700001701459700002201476856003701498 2008 eng d00aMultilevel effects in the Rabi oscillations of a Josephson phase qubit0 aMultilevel effects in the Rabi oscillations of a Josephson phase c2008/9/150 v783 a We present Rabi oscillation measurements of a Nb/AlOx/Nb dc superconducting quantum interference device (SQUID) phase qubit with a 100 um^2 area junction acquired over a range of microwave drive power and frequency detuning. Given the slightly anharmonic level structure of the device, several excited states play an important role in the qubit dynamics, particularly at high power. To investigate the effects of these levels, multiphoton Rabi oscillations were monitored by measuring the tunneling escape rate of the device to the voltage state, which is particularly sensitive to excited state population. We compare the observed oscillation frequencies with a simplified model constructed from the full phase qubit Hamiltonian and also compare time-dependent escape rate measurements with a more complete density-matrix simulation. Good quantitative agreement is found between the data and simulations, allowing us to identify a shift in resonance (analogous to the ac Stark effect), a suppression of the Rabi frequency, and leakage to the higher excited states. 1 aDutta, S., K.1 aStrauch, Frederick, W.1 aLewis, R., M.1 aMitra, Kaushik1 aPaik, Hanhee1 aPalomaki, T., A.1 aTiesinga, Eite1 aAnderson, J., R.1 aDragt, Alex, J.1 aLobb, C., J.1 aWellstood, F., C. uhttp://arxiv.org/abs/0806.4711v201766nas a2200181 4500008004100000245008100041210006900122260001500191300001800206490000800224520121000232100001701442700002401459700002001483700002001503700002401523856003701547 2008 eng d00aPolynomial-time quantum algorithm for the simulation of chemical dynamics 0 aPolynomialtime quantum algorithm for the simulation of chemical  c2008/11/24 a18681 - 186860 v1053 a The computational cost of exact methods for quantum simulation using classical computers grows exponentially with system size. As a consequence, these techniques can only be applied to small systems. By contrast, we demonstrate that quantum computers could exactly simulate chemical reactions in polynomial time. Our algorithm uses the split-operator approach and explicitly simulates all electron-nuclear and inter-electronic interactions in quadratic time. Surprisingly, this treatment is not only more accurate than the Born-Oppenheimer approximation, but faster and more efficient as well, for all reactions with more than about four atoms. This is the case even though the entire electronic wavefunction is propagated on a grid with appropriately short timesteps. Although the preparation and measurement of arbitrary states on a quantum computer is inefficient, here we demonstrate how to prepare states of chemical interest efficiently. We also show how to efficiently obtain chemically relevant observables, such as state-to-state transition probabilities and thermal reaction rates. Quantum computers using these techniques could outperform current classical computers with one hundred qubits. 1 aKassal, Ivan1 aJordan, Stephen, P.1 aLove, Peter, J.1 aMohseni, Masoud1 aAspuru-Guzik, Alán uhttp://arxiv.org/abs/0801.2986v301333nas a2200181 4500008004100000245004900041210004900090260001400139490000700153520083600160100001900996700002001015700001701035700002101052700002201073700001901095856003701114 2008 eng d00aQuantum behavior of the dc SQUID phase qubit0 aQuantum behavior of the dc SQUID phase qubit c2008/6/130 v773 a We analyze the behavior of a dc Superconducting Quantum Interference Device (SQUID) phase qubit in which one junction acts as a phase qubit and the rest of the device provides isolation from dissipation and noise in the bias leads. Ignoring dissipation, we find the two-dimensional Hamiltonian of the system and use numerical methods and a cubic approximation to solve Schrodinger's equation for the eigenstates, energy levels, tunneling rates, and expectation value of the currents in the junctions. Using these results, we investigate how well this design provides isolation while preserving the characteristics of a phase qubit. In addition, we show that the expectation value of current flowing through the isolation junction depends on the state of the qubit and can be used for non-destructive read out of the qubit state. 1 aMitra, Kaushik1 aStrauch, F., W.1 aLobb, C., J.1 aAnderson, J., R.1 aWellstood, F., C.1 aTiesinga, Eite uhttp://arxiv.org/abs/0805.3680v100566nas a2200181 4500008004100000245008800041210006900129300001100198490000800209100002500217700001200242700001500254700001500269700001400284700001600298700001900314856005100333 2008 eng d00aSuppression of Inelastic Collisions Between Polar Molecules With a Repulsive Shield0 aSuppression of Inelastic Collisions Between Polar Molecules With a0732010 v1011 aGorshkov, Alexey, V.1 aRabl, P1 aPupillo, G1 aMicheli, A1 aZoller, P1 aLukin, M, D1 aBüchler, H, P uhttp://link.aps.org/abstract/PRL/v101/e073201/01036nas a2200169 4500008004100000245009800041210006900139260001500208300001200223490000600235520049500241100001900736700001900755700002600774700002300800856004300823 2007 eng d00aEffective-range description of a Bose gas under strong one- or two-dimensional confinement 0 aEffectiverange description of a Bose gas under strong one or two c2007/01/29 a19 - 190 v93 a We point out that theories describing s-wave collisions of bosonic atoms confined in one- or two-dimensional geometries can be extended to much tighter confinements than previously thought. This is achieved by replacing the scattering length by an energy-dependent scattering length which was already introduced for the calculation of energy levels under 3D confinement. This replacement accurately predicts the position of confinement-induced resonances in strongly confined geometries. 1 aNaidon, Pascal1 aTiesinga, Eite1 aMitchell, William, F.1 aJulienne, Paul, S. uhttp://arxiv.org/abs/physics/0607140v202185nas a2200145 4500008004100000245006500041210006300106260001400169300001600183520173300199100001901932700002201951700002301973856004301996 2007 eng d00aQuantum Algorithms for Simon’s Problem over General Groups0 aQuantum Algorithms for Simon s Problem over General Groups c1/25/2007 a1217–12243 a

Daniel Simon's 1994 discovery of an efficient quantum algorithm for solving the hidden subgroup problem (HSP) over Zn2 provided one of the first algebraic problems for which quantum computers are exponentially faster than their classical counterparts. In this paper, we study the generalization of Simon's problem to arbitrary groups. Fixing a finite group G, this is the problem of recovering an involution m = (m1,...,mn) ε Gn from an oracle f with the property that f(x) = f(x · y) ⇔ y ε {1, m}. In the current parlance, this is the hidden subgroup problem (HSP) over groups of the form Gn, where G is a nonabelian group of constant size, and where the hidden subgroup is either trivial or has order two.

Although groups of the form Gn have a simple product structure, they share important representation-theoretic properties with the symmetric groups Sn, where a solution to the HSP would yield a quantum algorithm for Graph Isomorphism. In particular, solving their HSP with the so-called "standard method" requires highly entangled measurements on the tensor product of many coset states.

Here we give quantum algorithms with time complexity 2O(√n log n) that recover hidden involutions m = (m1,..., mn) ε Gn where, as in Simon's problem, each mi is either the identity or the conjugate of a known element m and there is a character X of G for which X(m) = - X(1). Our approach combines the general idea behind Kuperberg's sieve for dihedral groups with the "missing harmonic" approach of Moore and Russell. These are the first nontrivial hidden subgroup algorithms for group families that require highly entangled multiregister Fourier sampling.

1 aAlagic, Gorjan1 aMoore, Cristopher1 aRussell, Alexander uhttps://arxiv.org/abs/quant-ph/060325101375nas a2200181 4500008004100000245008800041210006900129260001400198490000700212520082100219100001901040700001801059700002001077700001501097700001901112700001801131856004401149 2007 eng d00aRelaxation, dephasing, and quantum control of electron spins in double quantum dots0 aRelaxation dephasing and quantum control of electron spins in do c2007/7/130 v763 aRecent experiments have demonstrated quantum manipulation of two-electron spin states in double quantum dots using electrically controlled exchange interactions. Here, we present a detailed theory for electron spin dynamics in two-electron double dot systems that was used to guide these experiments and analyze experimental results. The theory treats both charge and spin degrees of freedom on an equal basis. Specifically, we analyze the relaxation and dephasing mechanisms that are relevant to experiments and discuss practical approaches for quantum control of two-electron system. We show that both charge and spin dephasing play important roles in the dynamics of the two-spin system, but neither represents a fundamental limit for electrical control of spin degrees of freedom in semiconductor quantum bits. 1 aTaylor, J., M.1 aPetta, J., R.1 aJohnson, A., C.1 aYacoby, A.1 aMarcus, C., M.1 aLukin, M., D. uhttp://arxiv.org/abs/cond-mat/0602470v201734nas a2200229 4500008004100000245006500041210006500106260001500171520102700186100002301213700002501236700002601261700002201287700002001309700002101329700002501350700003001375700002301405700001901428700002001447856003701467 2007 eng d00aSignatures of incoherence in a quantum information processor0 aSignatures of incoherence in a quantum information processor c2007/05/243 a Incoherent noise is manifest in measurements of expectation values when the underlying ensemble evolves under a classical distribution of unitary processes. While many incoherent processes appear decoherent, there are important differences. The distribution functions underlying incoherent processes are either static or slowly varying with respect to control operations and so the errors introduced by these distributions are refocusable. The observation and control of incoherence in small Hilbert spaces is well known. Here we explore incoherence during an entangling operation, such as is relevant in quantum information processing. As expected, it is more difficult to separate incoherence and decoherence over such processes. However, by studying the fidelity decay under a cyclic entangling map we are able to identify distinctive experimental signatures of incoherence. This result is demonstrated both through numerical simulations and experimentally in a three qubit nuclear magnetic resonance implementation. 1 aHenry, Michael, K.1 aGorshkov, Alexey, V.1 aWeinstein, Yaakov, S.1 aCappellaro, Paola1 aEmerson, Joseph1 aBoulant, Nicolas1 aHodges, Jonathan, S.1 aRamanathan, Chandrasekhar1 aHavel, Timothy, F.1 aMartinez, Rudy1 aCory, David, G. uhttp://arxiv.org/abs/0705.3666v201845nas a2200145 4500008004100000245005400041210005100095260001500146300001200161520139800173100001601571700002401587700002401611856006401635 2006 eng d00aOn Bounded Distance Decoding for General Lattices0 aBounded Distance Decoding for General Lattices c2006/01/01 a450-4613 aA central problem in the algorithmic study of lattices is the closest vector problem: given a lattice L represented by some basis, and a target point y⃗ , find the lattice point closest to y⃗ . Bounded Distance Decoding is a variant of this problem in which the target is guaranteed to be close to the lattice, relative to the minimum distance λ1(L) of the lattice. Specifically, in the α-Bounded Distance Decoding problem (α-BDD), we are given a lattice L and a vector y⃗ (within distance α⋅λ1(L) from the lattice), and we are asked to find a lattice point x⃗ ∈L within distance α⋅λ1(L) from the target. In coding theory, the lattice points correspond to codewords, and the target points correspond to lattice points being perturbed by noise vectors. Since in coding theory the lattice is usually fixed, we may “pre-process” it before receiving any targets, to make the subsequent decoding faster. This leads us to consider α-BDD with pre-processing. We show how a recent technique of Aharonov and Regev [2] can be used to solve α-BDD with pre-processing in polynomial time for α=O((logn)/n−−−−−−−√). This improves upon the previously best known algorithm due to Klein [13] which solved the problem for α=O(1/n). We also establish hardness results for α-BDD and α-BDD with pre-processing, as well as generalize our results to other ℓ p norms.1 aLiu, Yi-Kai1 aLyubashevsky, Vadim1 aMicciancio, Daniele uhttp://link.springer.com/chapter/10.1007/11830924_41#page-106219nas a2200145 4500008004100000022001300041245011100054210006900165260001500234300001400249490000700263520571500270100001705985856007106002 2005 eng d a0040938300aExponential iterated integrals and the relative solvable completion of the fundamental group of a manifold0 aExponential iterated integrals and the relative solvable complet c2005/03/01 a351 - 3730 v443 a

We develop a class of integrals on a manifold M called exponential iterated integrals  , an extension of K.T. Chen's iterated integrals. It is shown that the matrix entries of any upper triangular representation of π1(M,x) can be expressed via these new integrals. The ring of exponential iterated integrals contains the coordinate rings for a class of universal representations, called the relative solvable completions   of π1(M,x). We consider exponential iterated integrals in the particular case of fibered knot complements, where the fundamental group always has a faithful relative solvable completion.

1 aMiller, Carl uhttp://www.sciencedirect.com/science/article/pii/S004093830400079501196nas a2200217 4500008004100000245005900041210005800100260001500158490000700173520059700180100001100777700001200788700002300800700001800823700001700841700001900858700001700877700002100894700001900915856004400934 2005 eng d00aSodium Bose-Einstein Condensates in an Optical Lattice0 aSodium BoseEinstein Condensates in an Optical Lattice c2005/10/100 v723 a The phase transition from a superfluid to a Mott insulator has been observed in a $^{23}$Na Bose-Einstein condensate. A dye laser detuned $\approx 5$nm red of the Na $3^2$S$ \to 3^2$P$_{1/2}$ transition was used to form the three dimensional optical lattice. The heating effects of the small detuning as well as the three-body decay processes constrained the timescale of the experiment. Certain lattice detunings were found to induce a large loss of atoms. These loss features were shown to be due to photoassociation of atoms to vibrational levels in the Na$_2$ $(1) ^3\Sigma_g^+$ state. 1 aXu, K.1 aLiu, Y.1 aAbo-Shaeer, J., R.1 aMukaiyama, T.1 aChin, J., K.1 aMiller, D., E.1 aKetterle, W.1 aJones, Kevin, M.1 aTiesinga, Eite uhttp://arxiv.org/abs/cond-mat/0507288v101053nas a2200181 4500008004100000245007400041210006900115260001400184490000700198520052300205100001900728700001300747700001500760700001500775700001900790700001800809856004400827 2005 eng d00aSolid-state circuit for spin entanglement generation and purification0 aSolidstate circuit for spin entanglement generation and purifica c2005/6/150 v943 aWe show how realistic charge manipulation and measurement techniques, combined with the exchange interaction, allow for the robust generation and purification of four-particle spin entangled states in electrically controlled semiconductor quantum dots. The generated states are immunized to the dominant sources of noise via a dynamical decoherence-free subspace; all additional errors are corrected by a purification protocol. This approach may find application in quantum computation, communication, and metrology. 1 aTaylor, J., M.1 aDür, W.1 aZoller, P.1 aYacoby, A.1 aMarcus, C., M.1 aLukin, M., D. uhttp://arxiv.org/abs/cond-mat/0503255v201168nas a2200133 4500008004100000245004200041210004200083260001400125520078800139100001900927700002200946700002300968856004300991 2005 eng d00aStrong Fourier Sampling Fails over Gn0 aStrong Fourier Sampling Fails over Gn c11/7/20053 a

We present a negative result regarding the hidden subgroup problem on the powers Gn of a fixed group G. Under a condition on the base group G, we prove that strong Fourier sampling cannot distinguish some subgroups of Gn. Since strong sampling is in fact the optimal measurement on a coset state, this shows that we have no hope of efficiently solving the hidden subgroup problem over these groups with separable measurements on coset states (that is, using any polynomial number of single-register coset state experiments). Base groups satisfying our condition include all nonabelian simple groups. We apply our results to show that there exist uniform families of nilpotent groups whose normal series factors have constant size and yet are immune to strong Fourier sampling.

1 aAlagic, Gorjan1 aMoore, Cristopher1 aRussell, Alexander uhttps://arxiv.org/abs/quant-ph/051105401386nas a2200265 4500008004100000245006600041210006500107260001500172300000900187490000700196520066500203100002100868700001800889700001300907700002100920700001700941700001300958700001100971700001500982700002200997700002301019700001901042700001501061856004401076 2004 eng d00aQuantum key distribution with 1.25 Gbps clock synchronization0 aQuantum key distribution with 125 Gbps clock synchronization c2004/05/17 a20110 v123 a We have demonstrated the exchange of sifted quantum cryptographic key over a 730 meter free-space link at rates of up to 1.0 Mbps, two orders of magnitude faster than previously reported results. A classical channel at 1550 nm operates in parallel with a quantum channel at 845 nm. Clock recovery techniques on the classical channel at 1.25 Gbps enable quantum transmission at up to the clock rate. System performance is currently limited by the timing resolution of our silicon avalanche photodiode detectors. With improved detector resolution, our technique will yield another order of magnitude increase in performance, with existing technology. 1 aBienfang, J., C.1 aGross, A., J.1 aMink, A.1 aHershman, B., J.1 aNakassis, A.1 aTang, X.1 aLu, R.1 aSu, D., H.1 aClark, Charles, W1 aWilliams, Carl, J.1 aHagley, E., W.1 aWen, Jesse uhttp://arxiv.org/abs/quant-ph/0405097v100456nas a2200121 4500008004100000245005600041210005500097100002300152700002300175700001500198700002600213856009500239 2003 eng d00aLanguage-reconfigurable universal phone recognition0 aLanguagereconfigurable universal phone recognition1 aWalker, Brenton, D1 aLackey, Bradley, C1 aMuller, JS1 aSchone, Patrick, John uhttps://www.quics.umd.edu/publications/language-reconfigurable-universal-phone-recognition01085nas a2200145 4500008004100000245005000041210004900091260001400140490000700154520067800161100001900839700001900858700001800877856004400895 2003 eng d00aLong-lived memory for mesoscopic quantum bits0 aLonglived memory for mesoscopic quantum bits c2003/5/200 v903 aWe describe a technique to create long-lived quantum memory for quantum bits in mesoscopic systems. Specifically we show that electronic spin coherence can be reversibly mapped onto the collective state of the surrounding nuclei. The coherent transfer can be efficient and fast and it can be used, when combined with standard resonance techniques, to reversibly store coherent superpositions on the time scale of seconds. This method can also allow for ``engineering'' entangled states of nuclear ensembles and efficiently manipulating the stored states. We investigate the feasibility of this method through a detailed analysis of the coherence properties of the system. 1 aTaylor, J., M.1 aMarcus, C., M.1 aLukin, M., D. uhttp://arxiv.org/abs/cond-mat/0301323v101212nas a2200145 4500008004100000245007400041210006900115260001400184490000700198520074500205100002300950700002400973700002500997856004401022 2001 eng d00aExact sampling from non-attractive distributions using summary states0 aExact sampling from nonattractive distributions using summary st c2001/2/220 v633 a Propp and Wilson's method of coupling from the past allows one to efficiently generate exact samples from attractive statistical distributions (e.g., the ferromagnetic Ising model). This method may be generalized to non-attractive distributions by the use of summary states, as first described by Huber. Using this method, we present exact samples from a frustrated antiferromagnetic triangular Ising model and the antiferromagnetic q=3 Potts model. We discuss the advantages and limitations of the method of summary states for practical sampling, paying particular attention to the slowing down of the algorithm at low temperature. In particular, we show that such a slowing down can occur in the absence of a physical phase transition. 1 aChilds, Andrew, M.1 aPatterson, Ryan, B.1 aMacKay, David, J. C. uhttp://arxiv.org/abs/cond-mat/0005132v1