01576nas a2200181 4500008004100000022001400041245006300055210006100118260001400179300001600193490000600209520107500215100001701290700001701307700001801324700001501342856003701357 2024 eng d a2475-142100aA Case for Synthesis of Recursive Quantum Unitary Programs0 aCase for Synthesis of Recursive Quantum Unitary Programs c12/5/2023 a1759–17880 v83 a

Quantum programs are notoriously difficult to code and verify due to unintuitive quantum knowledge associated with quantum programming. Automated tools relieving the tedium and errors associated with low-level quantum details would hence be highly desirable. In this paper, we initiate the study of program synthesis for quantum unitary programs that recursively define a family of unitary circuits for different input sizes, which are widely used in existing quantum programming languages. Specifically, we present QSynth, the first quantum program synthesis framework, including a new inductive quantum programming language, its specification, a sound logic for reasoning, and an encoding of the reasoning procedure into SMT instances. By leveraging existing SMT solvers, QSynth successfully synthesizes ten quantum unitary programs including quantum adder circuits, quantum eigenvalue inversion circuits and Quantum Fourier Transformation, which can be readily transpiled to executable programs on major quantum platforms, e.g., Q#, IBM Qiskit, and AWS Braket.

1 aDeng, Haowei1 aTao, Runzhou1 aPeng, Yuxiang1 aWu, Xiaodi uhttps://arxiv.org/abs/2311.1150300787nas a2200121 4500008004100000245005500041210005200096260001300148520042900161100002000590700001800610856003700628 2024 eng d00aFree Quantum Codes from Twisted Unitary $t$-groups0 aFree Quantum Codes from Twisted Unitary tgroups c2/2/20243 a

We introduce twisted unitary t-groups, a generalization of unitary t-groups under a twisting by an irreducible representation. We then apply representation theoretic methods to the Knill-Laflamme error correction conditions to show that twisted unitary t-groups automatically correspond to quantum codes with distance d=t+1. By construction these codes have many transversal gates, which are naturally fault tolerant.

1 aKubischta, Eric1 aTeixeira, Ian uhttps://arxiv.org/abs/2402.0163801404nas 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/2310.0705801664nas a2200133 4500008004100000245007400041210006900115260001400184520123900198100001801437700001301455700002501468856003701493 2024 eng d00aMulti-product Hamiltonian simulation with explicit commutator scaling0 aMultiproduct Hamiltonian simulation with explicit commutator sca c3/13/20243 a

The well-conditioned multi-product formula (MPF), proposed by [Low, Kliuchnikov, and Wiebe, 2019], is a simple high-order time-independent Hamiltonian simulation algorithm that implements a linear combination of standard product formulas of low order. While the MPF aims to simultaneously exploit commutator scaling among Hamiltonians and achieve near-optimal time and precision dependence, its lack of a rigorous error bound on the nested commutators renders its practical advantage ambiguous. In this work, we conduct a rigorous complexity analysis of the well-conditioned MPF, demonstrating explicit commutator scaling and near-optimal time and precision dependence at the same time. Using our improved complexity analysis, we present several applications of practical interest where the MPF based on a second-order product formula can achieve a polynomial speedup in both system size and evolution time, as well as an exponential speedup in precision, compared to second-order and even higher-order product formulas. Compared to post-Trotter methods, the MPF based on a second-order product formula can achieve polynomially better scaling in system size, with only poly-logarithmic overhead in evolution time and precision.

1 aAftab, Junaid1 aAn, Dong1 aTrivisa, Konstantina uhttps://arxiv.org/abs/2403.0892201874nas a2200181 4500008004100000245008500041210006900126260001400195300001100209490000600220520130000226100002301526700002301549700002001572700002201592700002101614856005701635 2024 eng d00aPrecision Bounds on Continuous-Variable State Tomography Using Classical Shadows0 aPrecision Bounds on ContinuousVariable State Tomography Using Cl c3/18/2024 a0103460 v53 a

Shadow tomography is a framework for constructing succinct descriptions of quantum states using randomized measurement bases, called “classical shadows,” with powerful methods to bound the estimators used. We recast existing experimental protocols for continuous-variable quantum state tomography in the classical-shadow framework, obtaining rigorous bounds on the number of independent measurements needed for estimating density matrices from these protocols. We analyze the efficiency of homodyne, heterodyne, photon-number-resolving, and photon-parity protocols. To reach a desired precision on the classical shadow of an N-photon density matrix with high probability, we show that homodyne detection requires order O(N4+1/3) measurements in the worst case, whereas photon-number-resolving and photon-parity detection require O (N4)measurements in the worst case (both up to logarithmic corrections). We benchmark these results against numerical simulation as well as experimental data from optical homodyne experiments. We find that numerical and experimental analyses of homodyne tomography match closely with our theoretical predictions. We extend our single-mode results to an efficient construction of multimode shadows based on local measurements.

1 aGandhari, Srilekha1 aAlbert, Victor, V.1 aGerrits, Thomas1 aTaylor, Jacob, M.1 aGullans, Michael uhttps://link.aps.org/doi/10.1103/PRXQuantum.5.01034602420nas 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/2303.0992201798nas a2200133 4500008004100000245007100041210006900112260001400181490000700195520137900202100002401581700002201605856003701627 2023 eng d00aColloquium: Advances in automation of quantum dot devices control0 aColloquium Advances in automation of quantum dot devices control c2/17/20230 v953 a

Arrays of quantum dots (QDs) are a promising candidate system to realize scalable, coupled qubit systems and serve as a fundamental building block for quantum computers. In such semiconductor quantum systems, devices now have tens of individual electrostatic and dynamical voltages that must be carefully set to localize the system into the single-electron regime and to realize good qubit operational performance. The mapping of requisite QD locations and charges to gate voltages presents a challenging classical control problem. With an increasing number of QD qubits, the relevant parameter space grows sufficiently to make heuristic control unfeasible. In recent years, there has been considerable effort to automate device control that combines script-based algorithms with machine learning (ML) techniques. In this Colloquium, a comprehensive overview of the recent progress in the automation of QD device control is presented, with a particular emphasis on silicon- and GaAs-based QDs formed in two-dimensional electron gases. Combining physics-based modeling with modern numerical optimization and ML has proven effective in yielding efficient, scalable control. Further integration of theoretical, computational, and experimental efforts with computer science and ML holds vast potential in advancing semiconductor and other platforms for quantum computing.

1 aZwolak, Justyna, P.1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2112.0936201846nas 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/2312.1432200422nas a2200133 4500008004100000245006200041210006100103260001400164490000800178100002400186700001900210700002200229856003700251 2023 eng d00aDecoherence from Long-Range Forces in Atom Interferometry0 aDecoherence from LongRange Forces in Atom Interferometry c3/17/20230 v1071 aKunjummen, Jonathan1 aCarney, Daniel1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2205.0300600804nas a2200121 4500008004100000245006000041210005800101260001400159520043400173100002000607700001800627856003700645 2023 eng d00aA Family of Quantum Codes with Exotic Transversal Gates0 aFamily of Quantum Codes with Exotic Transversal Gates c5/11/20233 a

Recently it has been shown that the binary icosahedral group 2I together with a certain involution forms the most efficient single-qubit universal gate set. In order for this to be viable, one must construct a quantum code with transversal gate group 2I, however, no such code has ever been demonstrated explicitly. We fill this void by constructing a novel family of quantum codes that all have transversal gate group 2I.

1 aKubischta, Eric1 aTeixeira, Ian uhttps://arxiv.org/abs/2305.0702301740nas a2200145 4500008004100000245008100041210006900122260001400191520125300205100003001458700002401488700002301512700002201535856003701557 2023 eng d00aFeasibility of a trapped atom interferometer with accelerating optical traps0 aFeasibility of a trapped atom interferometer with accelerating o c8/23/20233 a

In order to increase the measured phase of an atom interferometer and improve its sensitivity, researchers attempt to increase the enclosed space-time area using two methods: creating larger separations between the interferometer arms and having longer evolution times. However, increasing the evolution time reduces the bandwidth that can be sampled, whereas decreasing the evolution time worsens the sensitivity. In this paper, we attempt to address this by proposing a setup for high-bandwidth applications, with improved overall sensitivity. This is realized by accelerating and holding the atoms using optical dipole traps. We find that accelerations of up to 103-105 m/s2 can be achieved using acousto-optic deflectors (AODs) to move the traps. By comparing the sensitivity of our approach to acceleration as a baseline to traditional atom interferometry, we find a substantial improvement to the state of the art. In the limit of appropriate beam and optics stabilization, sensitivities approaching 10−14 (m/s2)/Hz−−−√ may be achievable at 1 Hz, while detection at 1 kHz with a sensitivity an order of magnitude better than traditional free-fall atom interferometers is possible with today's systems.

1 aPremawardhana, Gayathrini1 aKunjummen, Jonathan1 aSubhankar, Sarthak1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2308.1224602007nas a2200181 4500008004100000245010800041210006900149260001500218520141700233100002201650700001901672700001901691700002001710700001901730700001701749700002201766856003701788 2023 eng d00aA general approach to backaction-evading receivers with magnetomechanical and electromechanical sensors0 ageneral approach to backactionevading receivers with magnetomech c11/16/20233 a

Today's mechanical sensors are capable of detecting extremely weak perturbations while operating near the standard quantum limit. However, further improvements can be made in both sensitivity and bandwidth when we reduce the noise originating from the process of measurement itself -- the quantum-mechanical backaction of measurement -- and go below this 'standard' limit, possibly approaching the Heisenberg limit. One of the ways to eliminate this noise is by measuring a quantum nondemolition variable such as the momentum in a free-particle system. Here, we propose and characterize theoretical models for direct velocity measurement that utilize traditional electric and magnetic transducer designs to generate a signal while enabling this backaction evasion. We consider the general readout of this signal via electric or magnetic field sensing by creating toy models analogous to the standard optomechanical position-sensing problem, thereby facilitating the assessment of measurement-added noise. Using simple models that characterize a wide range of transducers, we find that the choice of readout scheme -- voltage or current -- for each mechanical detector configuration implies access to either the position or velocity of the mechanical sub-system. This in turn suggests a path forward for key fundamental physics experiments such as the direct detection of dark matter particles.

1 aRichman, Brittany1 aGhosh, Sohitri1 aCarney, Daniel1 aHiggins, Gerard1 aShawhan, Peter1 aLobb, C., J.1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2311.0958701778nas a2200157 4500008004100000245006400041210006300105260001400168520129800182100001301480700002201493700001901515700002401534700002501558856003701583 2023 eng d00aImproved Digital Quantum Simulation by Non-Unitary Channels0 aImproved Digital Quantum Simulation by NonUnitary Channels c7/24/20233 a

Simulating quantum systems is one of the most promising avenues to harness the computational power of quantum computers. However, hardware errors in noisy near-term devices remain a major obstacle for applications. Ideas based on the randomization of Suzuki-Trotter product formulas have been shown to be a powerful approach to reducing the errors of quantum simulation and lowering the gate count. In this paper, we study the performance of non-unitary simulation channels and consider the error structure of channels constructed from a weighted average of unitary circuits. We show that averaging over just a few simulation circuits can significantly reduce the Trotterization error for both single-step short-time and multi-step long-time simulations. We focus our analysis on two approaches for constructing circuit ensembles for averaging: (i) permuting the order of the terms in the Hamiltonian and (ii) applying a set of global symmetry transformations. We compare our analytical error bounds to empirical performance and show that empirical error reduction surpasses our analytical estimates in most cases. Finally, we test our method on an IonQ trapped-ion quantum computer accessed via the Amazon Braket cloud platform, and benchmark the performance of the averaging approach.

1 aGong, W.1 aKharkov, Yaroslav1 aTran, Minh, C.1 aBienias, Przemyslaw1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2307.1302801834nas 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/2309.1085601472nas a2200133 4500008004100000245008700041210006900128260001500197520101000212100002601222700003001248700002301278856003701301 2023 eng d00aNon-invertible symmetry-protected topological order in a group-based cluster state0 aNoninvertible symmetryprotected topological order in a groupbase c12/14/20233 a

Despite growing interest in beyond-group symmetries in quantum condensed matter systems, there are relatively few microscopic lattice models explicitly realizing these symmetries, and many phenomena have yet to be studied at the microscopic level. We introduce a one-dimensional stabilizer Hamiltonian composed of group-based Pauli operators whose ground state is a G×Rep(G)-symmetric state: the G cluster state introduced in Brell, New Journal of Physics 17, 023029 (2015) [at this http URL]. We show that this state lies in a symmetry-protected topological (SPT) phase protected by G×Rep(G) symmetry, distinct from the symmetric product state by a duality argument. We identify several signatures of SPT order, namely protected edge modes, string order parameters, and topological response. We discuss how G cluster states may be used as a universal resource for measurement-based quantum computation, explicitly working out the case where G is a semidirect product of abelian groups.

1 aFechisin, Christopher1 aTantivasadakarn, Nathanan1 aAlbert, Victor, V. uhttps://arxiv.org/abs/2312.0927201354nas a2200157 4500008004100000245006100041210005900102260001400161520088700175100002301062700001601085700002301101700002001124700001501144856003701159 2023 eng d00aA quantum central path algorithm for linear optimization0 aquantum central path algorithm for linear optimization c11/7/20233 a

We propose a novel quantum algorithm for solving linear optimization problems by quantum-mechanical simulation of the central path. While interior point methods follow the central path with an iterative algorithm that works with successive linearizations of the perturbed KKT conditions, we perform a single simulation working directly with the nonlinear complementarity equations. Combining our approach with iterative refinement techniques, we obtain an exact solution to a linear optimization problem involving m constraints and n variables using at most O((m+n)nnz(A)κ(M)L⋅polylog(m,n,κ(M))) elementary gates and O(nnz(A)L) classical arithmetic operations, where nnz(A) is the total number of non-zero elements found in the constraint matrix, L denotes binary input length of the problem data, and κ(M) is a condition number that depends only on the problem data.

1 aAugustino, Brandon1 aLeng, Jiaqi1 aNannicini, Giacomo1 aTerlaky, Tamás1 aWu, Xiaodi uhttps://arxiv.org/abs/2311.0397701590nas a2200217 4500008004100000245004000041210004000081260001400121520100000135100002101135700001601156700001501172700002201187700002001209700001901229700001901248700002101267700002201288700002501310856003701335 2023 eng d00aQuantum Sensing with Erasure Qubits0 aQuantum Sensing with Erasure Qubits c10/2/20233 a

The dominant noise in an "erasure qubit" is an erasure -- a type of error whose occurrence and location can be detected. Erasure qubits have potential to reduce the overhead associated with fault tolerance. To date, research on erasure qubits has primarily focused on quantum computing and quantum networking applications. Here, we consider the applicability of erasure qubits to quantum sensing and metrology. We show theoretically that, for the same level of noise, an erasure qubit acts as a more precise sensor or clock compared to its non-erasure counterpart. We experimentally demonstrate this by artificially injecting either erasure errors (in the form of atom loss) or dephasing errors into a differential optical lattice clock comparison, and observe enhanced precision in the case of erasure errors for the same injected error rate. Similar benefits of erasure qubits to sensing can be realized in other quantum platforms like Rydberg atoms and superconducting qubits

1 aNiroula, Pradeep1 aDolde, Jack1 aZheng, Xin1 aBringewatt, Jacob1 aEhrenberg, Adam1 aCox, Kevin, C.1 aThompson, Jeff1 aGullans, Michael1 aKolkowitz, Shimon1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2310.0151205435nas 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/2312.0973301610nas a2200157 4500008004100000245005000041210005000091260001300141490000800154520116900162100002401331700001901355700001901374700002201393856003701415 2023 eng d00aShadow process tomography of quantum channels0 aShadow process tomography of quantum channels c4/4/20230 v1073 a

Quantum process tomography is a critical capability for building quantum computers, enabling quantum networks, and understanding quantum sensors. Like quantum state tomography, the process tomography of an arbitrary quantum channel requires a number of measurements that scale exponentially in the number of quantum bits affected. However, the recent field of shadow tomography, applied to quantum states, has demonstrated the ability to extract key information about a state with only polynomially many measurements. In this work, we apply the concepts of shadow state tomography to the challenge of characterizing quantum processes. We make use of the Choi isomorphism to directly apply rigorous bounds from shadow state tomography to shadow process tomography, and we find additional bounds on the number of measurements that are unique to process tomography. Our results, which include algorithms for implementing shadow process tomography enable new techniques including evaluation of channel concatenation and the application of channels to shadows of quantum states. This provides a dramatic improvement for understanding large-scale quantum systems.

1 aKunjummen, Jonathan1 aTran, Minh, C.1 aCarney, Daniel1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2110.0362901475nas a2200121 4500008004100000245003200041210003200073260001400105520115600119100001901275700002201294856003701316 2023 eng d00aStrongly incoherent gravity0 aStrongly incoherent gravity c1/20/20233 a

While most fundamental interactions in nature are known to be mediated by quantized fields, the possibility has been raised that gravity may behave differently. Making this concept precise enough to test requires consistent models. Here we construct an explicit example of a theory where a non-entangling version of an arbitrary two-body potential V(r) arises from local measurements and feedback forces. While a variety of such theories exist, our construction causes particularly strong decoherence compared to more subtle approaches. Regardless, expectation values of observables obey the usual classical dynamics, while the interaction generates no entanglement. Applied to the Newtonian potential, this produces a non-relativistic model of gravity with fundamental loss of unitarity. The model contains a pair of free parameters, a substantial range of which is not excluded by observations to date. As an alternative to testing entanglement properties, we show that the entire remaining parameter space can be tested by looking for loss of quantum coherence in small systems like atom interferometers coupled to oscillating source masses.

1 aCarney, Daniel1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2301.0837801519nas a2200133 4500008004100000245008200041210006900123260001500192520106200207100002601269700003001295700002301325856003701348 2023 eng d00aSubsystem CSS codes, a tighter stabilizer-to-CSS mapping, and Goursat's Lemma0 aSubsystem CSS codes a tighter stabilizertoCSS mapping and Goursa c11/29/20233 a

The CSS code construction is a powerful framework used to express features of a quantum code in terms of a pair of underlying classical codes. Its subsystem extension allows for similar expressions, but the general case has not been fully explored. Extending previous work of Aly et. al. [quant-ph/0610153], we determine subsystem CSS code parameters, express codewords, and develop a Steane-type decoder using only data from the two underlying classical codes. We show that any subsystem stabilizer code can be ``doubled'' to yield a subsystem CSS code with twice the number of physical, logical, and gauge qudits and up to twice the code distance. This mapping preserves locality and is tighter than the Majorana-based mapping of Bravyi, Leemhuis, and Terhal [New J. Phys. 12 083039 (2010)]. Using Goursat's Lemma, we show that every subsystem stabilizer code can be constructed from two nested subsystem CSS codes satisfying certain constraints, and we characterize subsystem stabilizer codes based on the nested codes' properties.

1 aLiu, Michael, Liaofan1 aTantivasadakarn, Nathanan1 aAlbert, Victor, V. uhttps://arxiv.org/abs/2311.1800302721nas a2200253 4500008004100000245016100041210006900202260001400271300001100285490000600296520192600302100002002228700001502248700001802263700001902281700001802300700001902318700001602337700002102353700001402374700002202388700002002410856003702430 2022 eng d00aAccurate and Efficient Quantum Computations of Molecular Properties Using Daubechies Wavelet Molecular Orbitals: A Benchmark Study against Experimental Data0 aAccurate and Efficient Quantum Computations of Molecular Propert c5/28/2022 a0203600 v33 a

Although quantum computation (QC) is regarded as a promising numerical method for computational quantum chemistry, current applications of quantum-chemistry calculations on quantum computers are limited to small molecules. This limitation can be ascribed to technical problems in building and manipulating more qubits and the associated complicated operations of quantum gates in a quantum circuit when the size of the molecular system becomes large. As a result, reducing the number of required qubits is necessary to make QC practical. Currently, the minimal STO-3G basis set is commonly used in benchmark studies because it requires the minimum number of spin orbitals. Nonetheless, the accuracy of using STO-3G is generally low and thus cannot provide useful predictions. We propose to adopt Daubechies wavelet functions as an accurate and efficient method for QCs of molecular electronic properties. We demonstrate that a minimal basis set constructed from Daubechies wavelet basis can yield accurate results through a better description of the molecular Hamiltonian, while keeping the number of spin orbitals minimal. With the improved Hamiltonian through Daubechies wavelets, we calculate vibrational frequencies for H2 and LiH using quantum-computing algorithm to show that the results are in excellent agreement with experimental data. As a result, we achieve quantum calculations in which accuracy is comparable with that of the full configuration interaction calculation using the cc-pVDZ basis set, whereas the computational cost is the same as that of a STO-3G calculation. Thus, our work provides a more efficient and accurate representation of the molecular Hamiltonian for efficient QCs of molecular systems, and for the first time demonstrates that predictions in agreement with experimental measurements are possible to be achieved with quantum resources available in near-term quantum computers.

1 aHong, Cheng-Lin1 aTsai, Ting1 aChou, Jyh-Pin1 aChen, Peng-Jen1 aTsai, Pei-Kai1 aChen, Yu-Cheng1 aKuo, En-Jui1 aSrolovitz, David1 aHu, Alice1 aCheng, Yuan-Chung1 aGoan, Hsi-Sheng uhttps://arxiv.org/abs/2205.1447600829nam a2200145 4500008004100000245007900041210006900120260002000189300001100209520027900220100002400499700002100523700002800544856011100572 2022 eng d00aAnalogue Quantum Simulation: A New Instrument for Scientific Understanding0 aAnalogue Quantum Simulation A New Instrument for Scientific Unde bSpringer Nature a83-1023 a

Analyzes analogue quantum simulation philosophically. Provides a framework to support the goals of scientists. Useful to both working scientists and philosophers of science.

1 aHangleiter, Dominik1 aCarolan, Jacques1 aThébault, Karim, P. Y. uhttps://www.quics.umd.edu/publications/analogue-quantum-simulation-new-instrument-scientific-understanding02622nas a2200253 4500008004100000020002200041022001400063245012000077210006900197260001300266300001400279490000800293520178700301653003702088653004302125653002702168653003102195100002102226700002502247700001902272700001902291700002102310856003702331 2022 eng d a978-3-95977-237-2 a1868-896900aApproximating Output Probabilities of Shallow Quantum Circuits which are Geometrically-local in any Fixed Dimension0 aApproximating Output Probabilities of Shallow Quantum Circuits w c4/7/2022 a9:1--9:170 v2323 a

We present a classical algorithm that, for any D-dimensional geometrically-local, quantum circuit C of polylogarithmic-depth, and any bit string x∈0,1n, can compute the quantity |<x|C|0⊗n>|2 to within any inverse-polynomial additive error in quasi-polynomial time, for any fixed dimension D. This is an extension of the result [CC21], which originally proved this result for D=3. To see why this is interesting, note that, while the D=1 case of this result follows from standard use of Matrix Product States, known for decades, the D=2 case required novel and interesting techniques introduced in [BGM19]. Extending to the case D=3 was even more laborious and required further new techniques introduced in [CC21]. Our work here shows that, while handling each new dimension has historically required a new insight, and fixed algorithmic primitive, based on known techniques for D≤3, we can now handle any fixed dimension D>3.
Our algorithm uses the Divide-and-Conquer framework of [CC21] to approximate the desired quantity via several instantiations of the same problem type, each involving D-dimensional circuits on about half the number of qubits as the original. This division step is then applied recursively, until the width of the recursively decomposed circuits in the Dth dimension is so small that they can effectively be regarded as (D−1)-dimensional problems by absorbing the small width in the Dth dimension into the qudit structure at the cost of a moderate increase in runtime. The main technical challenge lies in ensuring that the more involved portions of the recursive circuit decomposition and error analysis from [CC21] still hold in higher dimensions, which requires small modifications to the analysis in some places.

10aComputational Complexity (cs.CC)10aFOS: Computer and information sciences10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aDontha, Suchetan1 aTan, Shi, Jie Samuel1 aSmith, Stephen1 aChoi, Sangheon1 aCoudron, Matthew uhttps://arxiv.org/abs/2202.0834902685nas a2200253 4500008004100000245007700041210006900118260001400187520182700201653002102028653002702049653004202076653003502118653003002153653003102183653005202214100002302266700001602289700002102305700002202326700003002348700001602378856003702394 2022 eng d00aCodimension-2 defects and higher symmetries in (3+1)D topological phases0 aCodimension2 defects and higher symmetries in 31D topological ph c8/15/20223 a

(3+1)D topological phases of matter can host a broad class of non-trivial topological defects of codimension-1, 2, and 3, of which the well-known point charges and flux loops are special cases. The complete algebraic structure of these defects defines a higher category, and can be viewed as an emergent higher symmetry. This plays a crucial role both in the classification of phases of matter and the possible fault-tolerant logical operations in topological quantum error correcting codes. In this paper, we study several examples of such higher codimension defects from distinct perspectives. We mainly study a class of invertible codimension-2 topological defects, which we refer to as twist strings. We provide a number of general constructions for twist strings, in terms of gauging lower dimensional invertible phases, layer constructions, and condensation defects. We study some special examples in the context of Z2 gauge theory with fermionic charges, in Z2×Z2 gauge theory with bosonic charges, and also in non-Abelian discrete gauge theories based on dihedral (Dn) and alternating (A6) groups. The intersection between twist strings and Abelian flux loops sources Abelian point charges, which defines an H4 cohomology class that characterizes part of an underlying 3-group symmetry of the topological order. The equations involving background gauge fields for the 3-group symmetry have been explicitly written down for various cases. We also study examples of twist strings interacting with non-Abelian flux loops (defining part of a non-invertible higher symmetry), examples of non-invertible codimension-2 defects, and examples of interplay of codimension-2 defects with codimension-1 defects. We also find an example of geometric, not fully topological, twist strings in (3+1)D A6 gauge theory.

10aFOS: Mathematics10aFOS: Physical sciences10aHigh Energy Physics - Theory (hep-th)10aMathematical Physics (math-ph)10aQuantum Algebra (math.QA)10aQuantum Physics (quant-ph)10aStrongly Correlated Electrons (cond-mat.str-el)1 aBarkeshli, Maissam1 aChen, Yu-An1 aHuang, Sheng-Jie1 aKobayashi, Ryohei1 aTantivasadakarn, Nathanan1 aZhu, Guanyu uhttps://arxiv.org/abs/2208.0736701776nas a2200181 4500008004100000245004200041210004100083260001400124520125200138653002701390653003101417100002301448700002301471700002001494700002201514700002101536856003701557 2022 eng d00aContinuous-Variable Shadow Tomography0 aContinuousVariable Shadow Tomography c11/9/20223 a

Shadow tomography is a framework for constructing succinct descriptions of quantum states, called classical shadows, with powerful methods to bound the estimators used. We recast existing experimental protocols for continuous-variable tomography in the classical-shadow framework, obtaining rigorous bounds on the sample complexity for estimating density matrices from these protocols. We analyze the efficiency of homodyne, heterodyne, photon number resolving (PNR), and photon-parity protocols. To reach a desired precision on the classical shadow of an N-photon density matrix with a high probability, we show that homodyne detection requires an order O(N5) measurements in the worst case, whereas PNR and photon-parity detection require O(N4) measurements in the worst case (both up to logarithmic corrections). We benchmark these results against numerical simulation as well as experimental data from optical homodyne experiments. We find that numerical and experimental homodyne tomography significantly outperforms our bounds, exhibiting a more typical scaling of the number of measurements that is close to linear in N. We extend our single-mode results to an efficient construction of multimode shadows based on local measurements.

10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aGandhari, Srilekha1 aAlbert, Victor, V.1 aGerrits, Thomas1 aTaylor, Jacob, M.1 aGullans, Michael uhttps://arxiv.org/abs/2211.0514901827nas a2200181 4500008004100000245005500041210005500096260001400151490000600165520130500171100002301476700001601499700001501515700002001530700003001550700002801580856003701608 2022 eng d00aPauli Stabilizer Models of Twisted Quantum Doubles0 aPauli Stabilizer Models of Twisted Quantum Doubles c3/30/20220 v33 a

We construct a Pauli stabilizer model for every two-dimensional Abelian topological order that admits a gapped boundary. Our primary example is a Pauli stabilizer model on four-dimensional qudits that belongs to the double semion (DS) phase of matter. The DS stabilizer Hamiltonian is constructed by condensing an emergent boson in a Z4 toric code, where the condensation is implemented by making certain two-body measurements. We rigorously verify the topological order of the DS stabilizer model by identifying an explicit finite-depth quantum circuit (with ancillary qubits) that maps its ground state subspace to that of a DS string-net model. We show that the construction of the DS stabilizer Hamiltonian generalizes to all twisted quantum doubles (TQDs) with Abelian anyons. This yields a Pauli stabilizer code on composite-dimensional qudits for each such TQD, implying that the classification of topological Pauli stabilizer codes extends well beyond stacks of toric codes - in fact, exhausting all Abelian anyon theories that admit a gapped boundary. We also demonstrate that symmetry-protected topological phases of matter characterized by type I and type II cocycles can be modeled by Pauli stabilizer Hamiltonians by gauging certain 1-form symmetries of the TQD stabilizer models.

1 aEllison, Tyler, D.1 aChen, Yu-An1 aDua, Arpit1 aShirley, Wilbur1 aTantivasadakarn, Nathanan1 aWilliamson, Dominic, J. uhttps://arxiv.org/abs/2112.1139402246nas a2200205 4500008004100000245006600041210006600107260001400173520157400187653002701761653003101788653005201819100002301871700001601894700001501910700002001925700003001945700002801975856003702003 2022 eng d00aPauli topological subsystem codes from Abelian anyon theories0 aPauli topological subsystem codes from Abelian anyon theories c11/7/20223 a

We construct Pauli topological subsystem codes characterized by arbitrary two-dimensional Abelian anyon theories--this includes anyon theories with degenerate braiding relations and those without a gapped boundary to the vacuum. Our work both extends the classification of two-dimensional Pauli topological subsystem codes to systems of composite-dimensional qudits and establishes that the classification is at least as rich as that of Abelian anyon theories. We exemplify the construction with topological subsystem codes defined on four-dimensional qudits based on the Z(1)4 anyon theory with degenerate braiding relations and the chiral semion theory--both of which cannot be captured by topological stabilizer codes. The construction proceeds by "gauging out" certain anyon types of a topological stabilizer code. This amounts to defining a gauge group generated by the stabilizer group of the topological stabilizer code and a set of anyonic string operators for the anyon types that are gauged out. The resulting topological subsystem code is characterized by an anyon theory containing a proper subset of the anyons of the topological stabilizer code. We thereby show that every Abelian anyon theory is a subtheory of a stack of toric codes and a certain family of twisted quantum doubles that generalize the double semion anyon theory. We further prove a number of general statements about the logical operators of translation invariant topological subsystem codes and define their associated anyon theories in terms of higher-form symmetries.

10aFOS: Physical sciences10aQuantum Physics (quant-ph)10aStrongly Correlated Electrons (cond-mat.str-el)1 aEllison, Tyler, D.1 aChen, Yu-An1 aDua, Arpit1 aShirley, Wilbur1 aTantivasadakarn, Nathanan1 aWilliamson, Dominic, J. uhttps://arxiv.org/abs/2211.0379802380nas 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/2110.0694201744nas a2200169 4500008004100000245007100041210006900112260001400181490000800195520123200203100002101435700001901456700002001475700002301495700001901518856003701537 2022 eng d00aProvably efficient machine learning for quantum many-body problems0 aProvably efficient machine learning for quantum manybody problem c9/26/20220 v3773 a

Classical machine learning (ML) provides a potentially powerful approach to solving challenging quantum many-body problems in physics and chemistry. However, the advantages of ML over more traditional methods have not been firmly established. In this work, we prove that classical ML algorithms can efficiently predict ground state properties of gapped Hamiltonians in finite spatial dimensions, after learning from data obtained by measuring other Hamiltonians in the same quantum phase of matter. In contrast, under widely accepted complexity theory assumptions, classical algorithms that do not learn from data cannot achieve the same guarantee. We also prove that classical ML algorithms can efficiently classify a wide range of quantum phases of matter. Our arguments are based on the concept of a classical shadow, a succinct classical description of a many-body quantum state that can be constructed in feasible quantum experiments and be used to predict many properties of the state. Extensive numerical experiments corroborate our theoretical results in a variety of scenarios, including Rydberg atom systems, 2D random Heisenberg models, symmetry-protected topological phases, and topologically ordered phases.

1 aHuang, Hsin-Yuan1 aKueng, Richard1 aTorlai, Giacomo1 aAlbert, Victor, V.1 aPreskill, John uhttps://arxiv.org/abs/2106.1262701392nas 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/2203.0724201763nas 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/2103.0957701959nas a2200217 4500008004100000245010400041210006900145260001400214520119900228653002701427653003501454653003101489653005201520100002001572700001601592700001501608700002301623700003001646700002801676856003701704 2022 eng d00aThree-dimensional quantum cellular automata from chiral semion surface topological order and beyond0 aThreedimensional quantum cellular automata from chiral semion su c2/10/20223 a

We construct a novel three-dimensional quantum cellular automaton (QCA) based on a system with short-range entangled bulk and chiral semion boundary topological order. We argue that either the QCA is nontrivial, i.e. not a finite-depth circuit of local quantum gates, or there exists a two-dimensional commuting projector Hamiltonian realizing the chiral semion topological order (characterized by U(1)2 Chern-Simons theory). Our QCA is obtained by first constructing the Walker-Wang Hamiltonian of a certain premodular tensor category of order four, then condensing the deconfined bulk boson at the level of lattice operators. We show that the resulting Hamiltonian hosts chiral semion surface topological order in the presence of a boundary and can be realized as a non-Pauli stabilizer code on qubits, from which the QCA is defined. The construction is then generalized to a class of QCAs defined by non-Pauli stabilizer codes on 2n-dimensional qudits that feature surface anyons described by U(1)2n Chern-Simons theory. Our results support the conjecture that the group of nontrivial three-dimensional QCAs is isomorphic to the Witt group of non-degenerate braided fusion categories.

10aFOS: Physical sciences10aMathematical Physics (math-ph)10aQuantum Physics (quant-ph)10aStrongly Correlated Electrons (cond-mat.str-el)1 aShirley, Wilbur1 aChen, Yu-An1 aDua, Arpit1 aEllison, Tyler, D.1 aTantivasadakarn, Nathanan1 aWilliamson, Dominic, J. uhttps://arxiv.org/abs/2202.0544201880nas 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/2108.0004301979nas 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/2110.0107901456nas a2200145 4500008004100000245007500041210006900116260001400185300001100199490000600210520101600216100002201232700001901254856003701273 2021 eng d00aCirculation by microwave-induced vortex transport for signal isolation0 aCirculation by microwaveinduced vortex transport for signal isol c6/14/2021 a0303090 v23 a

Magnetic fields break time-reversal symmetry, which is leveraged in many settings to enable the nonreciprocal behavior of light. This is the core physics of circulators and other elements used in a variety of microwave and optical settings. Commercial circulators in the microwave domain typically use ferromagnetic materials and wave interference, requiring large devices and large fields. However, quantum information devices for sensing and computation require small sizes, lower fields, and better on-chip integration. Equivalences to ferromagnetic order---such as the XY model---can be realized at much lower magnetic fields by using arrays of superconducting islands connected by Josephson junctions. Here we show that the quantum-coherent motion of a single vortex in such an array suffices to induce nonreciprocal behavior, enabling a small-scale, moderate-bandwidth, and low insertion loss circulator at very low magnetic fields and at microwave frequencies relevant for experiments with qubits.

1 aRichman, Brittany1 aTaylor, J., M. uhttps://arxiv.org/abs/2010.0411801670nas a2200145 4500008004100000245008900041210006900130260001500199520119300214100002001407700001601427700001901443700002501462856003701487 2021 eng d00aClustering of steady-state correlations in open systems with long-range interactions0 aClustering of steadystate correlations in open systems with long c10/28/20213 a

Lieb-Robinson bounds are powerful analytical tools for constraining the dynamic and static properties of non-relativistic quantum systems. Recently, a complete picture for closed systems that evolve unitarily in time has been achieved. In experimental systems, however, interactions with the environment cannot generally be ignored, and the extension of Lieb-Robinson bounds to dissipative systems which evolve non-unitarily in time remains an open challenge. In this work, we prove two Lieb-Robinson bounds that constrain the dynamics of open quantum systems with long-range interactions that decay as a power-law in the distance between particles. Using a combination of these Lieb-Robinson bounds and mixing bounds which arise from "reversibility" -- naturally satisfied for thermal environments -- we prove the clustering of correlations in the steady states of open quantum systems with long-range interactions. Our work provides an initial step towards constraining the steady-state entanglement structure for a broad class of experimental platforms, and we highlight several open directions regarding the application of Lieb-Robinson bounds to dissipative systems.

1 aGuo, Andrew, Y.1 aLieu, Simon1 aTran, Minh, C.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2110.1536800790nas 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/2111.0466702085nas 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/2105.0108702034nas a2200181 4500008004100000245008100041210006900122260001300191490000800204520146900212100001801681700002501699700002001724700002301744700002501767700002301792856003701815 2021 eng d00aEfficient quantum algorithm for dissipative nonlinear differential equations0 aEfficient quantum algorithm for dissipative nonlinear differenti c3/1/20210 v1183 a

While there has been extensive previous work on efficient quantum algorithms for linear differential equations, analogous progress for nonlinear differential equations has been severely limited due to the linearity of quantum mechanics. Despite this obstacle, we develop a quantum algorithm for initial value problems described by dissipative quadratic n-dimensional ordinary differential equations. Assuming R<1, where R is a parameter characterizing the ratio of the nonlinearity to the linear dissipation, this algorithm has complexity T2poly(logT,logn)/ϵ, where T is the evolution time and ϵ is the allowed error in the output quantum state. This is an exponential improvement over the best previous quantum algorithms, whose complexity is exponential in T. We achieve this improvement using the method of Carleman linearization, for which we give an improved convergence theorem. This method maps a system of nonlinear differential equations to an infinite-dimensional system of linear differential equations, which we discretize, truncate, and solve using the forward Euler method and the quantum linear system algorithm. We also provide a lower bound on the worst-case complexity of quantum algorithms for general quadratic differential equations, showing that the problem is intractable for R≥2–√. Finally, we discuss potential applications of this approach to problems arising in biology as well as in fluid and plasma dynamics.

1 aLiu, Jin-Peng1 aKolden, Herman, Øie1 aKrovi, Hari, K.1 aLoureiro, Nuno, F.1 aTrivisa, Konstantina1 aChilds, Andrew, M. uhttps://arxiv.org/abs/2011.0318500984nas 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/2108.1247701880nas a2200169 4500008004100000022001400041245006100055210006100116260001400177490000600191520140600197100001901603700001301622700001901635700001901654856003701673 2021 eng d a2691-339900aFaster Digital Quantum Simulation by Symmetry Protection0 aFaster Digital Quantum Simulation by Symmetry Protection c2/14/20210 v23 a

Simulating the dynamics of quantum systems is an important application of quantum computers and has seen a variety of implementations on current hardware. We show that by introducing quantum gates implementing unitary transformations generated by the symmetries of the system, one can induce destructive interference between the errors from different steps of the simulation, effectively giving faster quantum simulation by symmetry protection. We derive rigorous bounds on the error of a symmetry-protected simulation algorithm and identify conditions for optimal symmetry protection. In particular, when the symmetry transformations are chosen as powers of a unitary, the error of the algorithm is approximately projected to the so-called quantum Zeno subspaces. We prove a bound on this approximation error, exponentially improving a recent result of Burgarth, Facchi, Gramegna, and Pascazio. We apply our technique to the simulations of the XXZ Heisenberg interactions with local disorder and the Schwinger model in quantum field theory. For both systems, our algorithm can reduce the simulation error by several orders of magnitude over the unprotected simulation. Finally, we provide numerical evidence suggesting that our technique can also protect simulation against other types of coherent, temporally correlated errors, such as the 1/f noise commonly found in solid-state experiments.

1 aTran, Minh, C.1 aSu, Yuan1 aCarney, Daniel1 aTaylor, J., M. uhttps://arxiv.org/abs/2006.1624801484nas a2200121 4500008004100000245010000041210006900141260001300210520107200223100001601295700001401311856003701325 2021 eng d00aHigher cup products on hypercubic lattices: application to lattice models of topological phases0 aHigher cup products on hypercubic lattices application to lattic c6/9/20213 a

In this paper, we derive the explicit formula for higher cup products on hypercubic lattices, based on the recently developed geometrical interpretation in the simplicial case. We illustrate how this formalism can elucidate lattice constructions on hypercubic lattices for various models and deriving them from spacetime actions. In particular, we demonstrate explicitly that the (3+1)D SPT S=12∫w22+w41 (where w1 and w2 are the first and second Stiefel-Whitney classes) is dual to the 3-fermion Walker-Wang model constructed on the cubic lattice by Burnell-Chen-Fidkowski-Vishwanath. Other examples include the double-semion model, and also the `fermionic' toric code in arbitrary dimensions on hypercubic lattices. In addition, we extend previous constructions of exact boson-fermion dualities and the Gu-Wen Grassmann Integral to arbitrary dimensions. Another result which may be of independent interest is a derivation of a cochain-level action for the generalized double-semion model, reproducing a recently derived action on the cohomology level.

1 aChen, Yu-An1 aTata, Sri uhttps://arxiv.org/abs/2106.0527401060nas a2200133 4500008004100000245004300041210004300084260001400127520067500141100002100816700002400837700002800861856003700889 2021 eng d00aHow to engineer a quantum wavefunction0 aHow to engineer a quantum wavefunction c12/2/20213 a

In a conventional experiment, inductive inferences between source and target systems are typically justified with reference to a uniformity principle between systems of the same material type. In an analogue quantum simulation, by contrast, scientists aim to learn about target quantum systems of one material type via an experiment on a source quantum system of a different material type. In this paper, we argue that such an inference can be justified by reference to the two quantum systems being of the same empirical type. We illustrate this novel experimental practice of wavefunction engineering with reference to the example of Bose-Hubbard systems. 

1 aEvans, Peter, W.1 aHangleiter, Dominik1 aThébault, Karim, P. Y. uhttps://arxiv.org/abs/2112.0110501198nas a2200169 4500008004100000245006000041210005400101260001400155520069100169100001900860700002000879700002900899700002000928700002500948700001800973856003700991 2021 eng d00aThe Lieb-Robinson light cone for power-law interactions0 aLiebRobinson light cone for powerlaw interactions c3/29/20213 a

The Lieb-Robinson theorem states that information propagates with a finite velocity in quantum systems on a lattice with nearest-neighbor interactions. What are the speed limits on information propagation in quantum systems with power-law interactions, which decay as 1/rα at distance r? Here, we present a definitive answer to this question for all exponents α>2d and all spatial dimensions d. Schematically, information takes time at least rmin{1,α−2d} to propagate a distance~r. As recent state transfer protocols saturate this bound, our work closes a decades-long hunt for optimal Lieb-Robinson bounds on quantum information dynamics with power-law interactions.

1 aTran, Minh, C.1 aGuo, Andrew, Y.1 aBaldwin, Christopher, L.1 aEhrenberg, Adam1 aGorshkov, Alexey, V.1 aLucas, Andrew uhttps://arxiv.org/abs/2103.1582801277nas a2200169 4500008004100000022001400041245006300055210006300118260001400181490000800195520078700203100001900990700001901009700002001028700002201048856003701070 2021 eng d a2470-002900aProposal for gravitational direct detection of dark matter0 aProposal for gravitational direct detection of dark matter c8/23/20210 v1023 a

The only coupling dark matter is guaranteed to have with the standard model is through gravity. Here we propose a concept for direct dark matter detection using only this gravitational coupling. We suggest that an array of quantum-limited mechanical impulse sensors may be capable of detecting the correlated gravitational force created by a passing dark matter particle. We consider the effects of irreducible noise from couplings of the sensors to the environment and noise due to the quantum measurement process. We show that the signal from Planck-scale dark matter is in principle detectable using a large number of gram-scale sensors in a meter-scale array with sufficiently low quantum noise, and discuss some experimental challenges en route to achieving this target.

1 aCarney, Daniel1 aGhosh, Sohitri1 aKrnjaic, Gordan1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/1903.0049202275nas 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/2102.1178401340nas 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/2101.1162902331nas a2200181 4500008004100000245005200041210005200093260001300145300000700158490000700165520185000172100002302022700001302045700001902058700001802077700001702095856003702112 2021 eng d00aTheory of Trotter Error with Commutator Scaling0 aTheory of Trotter Error with Commutator Scaling c2/1/2021 a490 v113 a

The Lie-Trotter formula, together with its higher-order generalizations, provides a direct approach to decomposing the exponential of a sum of operators. Despite significant effort, the error scaling of such product formulas remains poorly understood. We develop a theory of Trotter error that overcomes the limitations of prior approaches based on truncating the Baker-Campbell-Hausdorff expansion. Our analysis directly exploits the commutativity of operator summands, producing tighter error bounds for both real- and imaginary-time evolutions. Whereas previous work achieves similar goals for systems with geometric locality or Lie-algebraic structure, our approach holds in general. We give a host of improved algorithms for digital quantum simulation and quantum Monte Carlo methods, including simulations of second-quantized plane-wave electronic structure, k-local Hamiltonians, rapidly decaying power-law interactions, clustered Hamiltonians, the transverse field Ising model, and quantum ferromagnets, nearly matching or even outperforming the best previous results. We obtain further speedups using the fact that product formulas can preserve the locality of the simulated system. Specifically, we show that local observables can be simulated with complexity independent of the system size for power-law interacting systems, which implies a Lieb-Robinson bound as a byproduct. Our analysis reproduces known tight bounds for first- and second-order formulas. Our higher-order bound overestimates the complexity of simulating a one-dimensional Heisenberg model with an even-odd ordering of terms by only a factor of 5, and is close to tight for power-law interactions and other orderings of terms. This suggests that our theory can accurately characterize Trotter error in terms of both asymptotic scaling and constant prefactor.

1 aChilds, Andrew, M.1 aSu, Yuan1 aTran, Minh, C.1 aWiebe, Nathan1 aZhu, Shuchen uhttps://arxiv.org/abs/1912.0885401337nas 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/2104.0573701048nas a2200193 4500008004100000022001400041245006900055210006900124260001400193300001100207490000700218520051000225100001900735700001600754700001400770700001900784700001400803856003700817 2021 eng d a1367-263000aUltralight dark matter detection with mechanical quantum sensors0 aUltralight dark matter detection with mechanical quantum sensors c3/10/2021 a0230410 v233 a

We consider the use of quantum-limited mechanical force sensors to detect ultralight (sub-meV) dark matter candidates which are weakly coupled to the standard model. We show that mechanical sensors with masses around or below the milligram scale, operating around the standard quantum limit, would enable novel searches for dark matter with natural frequencies around the kHz scale. This would complement existing strategies based on torsion balances, atom interferometers, and atomic clock systems

1 aCarney, Daniel1 aHook, Anson1 aLiu, Zhen1 aTaylor, J., M.1 aZhao, Yue uhttps://arxiv.org/abs/1908.0479701487nas 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.2.03033002481nas 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/1909.0803001337nas a2200157 4500008004100000245007600041210006900117260001400186490000800200520085400208100001901062700001901081700001901100700001901119856004101138 2020 eng d00aBack-action evading impulse measurement with mechanical quantum sensors0 aBackaction evading impulse measurement with mechanical quantum s c8/28/20200 v1023 a

The quantum measurement of any observable naturally leads to noise added by the act of measurement. Approaches to evade or reduce this noise can lead to substantial improvements in a wide variety of sensors, from laser interferometers to precision magnetometers and more. In this paper, we develop a measurement protocol based upon pioneering work by the gravitational wave community which allows for reduction of added noise from measurement by coupling an optical field to the momentum of a small mirror. As a specific implementation, we present a continuous measurement protocol using a double-ring optomechanical cavity. We demonstrate that with experimentally-relevant parameters, this protocol can lead to significant back-action noise evasion, yielding measurement noise below the standard quantum limit over many decades of frequency.

1 aGhosh, Sohitri1 aCarney, Daniel1 aShawhan, Peter1 aTaylor, J., M. uhttps://arxiv.org/pdf/1910.11892.pdf01291nas a2200169 4500008004100000245005900041210005900100260001400159300000900173490000900182520082200191100001701013700001801030700001901048700001701067856003701084 2020 eng d00aBuilding Bulk Geometry from the Tensor Radon Transform0 aBuilding Bulk Geometry from the Tensor Radon Transform c12/4/2020 a1-500 v20203 a

Using the tensor Radon transform and related numerical methods, we study how bulk geometries can be explicitly reconstructed from boundary entanglement entropies in the specific case of AdS3/CFT2. We find that, given the boundary entanglement entropies of a 2d CFT, this framework provides a quantitative measure that detects whether the bulk dual is geometric in the perturbative (near AdS) limit. In the case where a well-defined bulk geometry exists, we explicitly reconstruct the unique bulk metric tensor once a gauge choice is made. We then examine the emergent bulk geometries for static and dynamical scenarios in holography and in many-body systems. Apart from the physics results, our work demonstrates that numerical methods are feasible and effective in the study of bulk reconstruction in AdS/CFT.

1 aCao, ChunJun1 aQ, Xiao-Liang1 aSwingle, Brian1 aTang, Eugene uhttps://arxiv.org/abs/2007.0000401525nas a2200181 4500008004100000245006100041210006100102260001500163300001100178490000600189520101100195100001601206700001801222700001701240700002401257700002501281856003701306 2020 eng d00aCircuit Complexity across a Topological Phase Transition0 aCircuit Complexity across a Topological Phase Transition c03/16/2020 a0133230 v23 a

We use Nielsen's approach to quantify the circuit complexity in the one-dimensional Kitaev model. In equilibrium, we find that the circuit complexity of ground states exhibits a divergent derivative at the critical point, signaling the presence of a topological phase transition. Out of equilibrium, we study the complexity dynamics after a sudden quench, and find that the steady-state complexity exhibits nonanalytical behavior when quenched across critical points. We generalize our results to the long-range interacting case, and demonstrate that the circuit complexity correctly predicts the critical point between regions with different semi-integer topological numbers. Our results establish a connection between circuit complexity and quantum phase transitions both in and out of equilibrium, and can be easily generalized to topological phase transitions in higher dimensions. Our study opens a new avenue to using circuit complexity as a novel quantity to understand many-body systems.

1 aLiu, Fangli1 aLundgren, Rex1 aTitum, Paraj1 aGarrison, James, R.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1902.1072001669nas 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-heli01561nas a2200169 4500008004100000245007300041210006900114260001300183490000800196520105300204100001901257700001701276700001301293700002301306700002501329856003701354 2020 eng d00aDestructive Error Interference in Product-Formula Lattice Simulation0 aDestructive Error Interference in ProductFormula Lattice Simulat c6/4/20200 v1243 a

Quantum computers can efficiently simulate the dynamics of quantum systems. In this paper, we study the cost of digitally simulating the dynamics of several physically relevant systems using the first-order product formula algorithm. We show that the errors from different Trotterization steps in the algorithm can interfere destructively, yielding a much smaller error than previously estimated. In particular, we prove that the total error in simulating a nearest-neighbor interacting system of n sites for time t using the first-order product formula with r time slices is O(nt/r+nt3/r2) when nt2/r is less than a small constant. Given an error tolerance ε, the error bound yields an estimate of max{O(n2t/ε),O(n2t3/2/ε1/2)} for the total gate count of the simulation. The estimate is tighter than previous bounds and matches the empirical performance observed in Childs et al. [PNAS 115, 9456-9461 (2018)]. We also provide numerical evidence for potential improvements and conjecture an even tighter estimate for the gate count. 

1 aTran, Minh, C.1 aChu, Su-Kuan1 aSu, Yuan1 aChilds, Andrew, M.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1912.1104701216nas a2200157 4500008004100000245005000041210005000091260001500141490000800156520078000164100001900944700001900963700002000982700001901002856003701021 2020 eng d00aGravitational Direct Detection of Dark Matter0 aGravitational Direct Detection of Dark Matter c10/13/20200 v1023 a

The only coupling dark matter is guaranteed to have with the standard model is through gravity. Here we propose a concept for direct dark matter detection using only this gravitational coupling, enabling a new regime of detection. Leveraging dramatic advances in the ability to create, maintain, and probe quantum states of massive objects, we suggest that an array of quantum-limited impulse sensors may be capable of detecting the correlated gravitational force created by a passing dark matter particle. We present two concrete realizations of this scheme, using either mechanical resonators or freely-falling masses. With currently available technology, a meter-scale apparatus of this type could detect any dark matter candidate around the Planck mass or heavier.

1 aCarney, Daniel1 aGhosh, Sohitri1 aKrnjaic, Gordan1 aTaylor, J., M. uhttps://arxiv.org/abs/1903.0049202312nas a2200217 4500008004100000245006500041210006400106260001400170490000700184520168700191100001901878700001901897700002001916700002001936700002301956700001601979700001901995700002502014700001802039856003702057 2020 eng d00aHierarchy of linear light cones with long-range interactions0 aHierarchy of linear light cones with longrange interactions c5/29/20200 v103 a

In quantum many-body systems with local interactions, quantum information and entanglement cannot spread outside of a "linear light cone," which expands at an emergent velocity analogous to the speed of light. Yet most non-relativistic physical systems realized in nature have long-range interactions: two degrees of freedom separated by a distance r interact with potential energy V(r)∝1/rα. In systems with long-range interactions, we rigorously establish a hierarchy of linear light cones: at the same α, some quantum information processing tasks are constrained by a linear light cone while others are not. In one spatial dimension, commutators of local operators ⟨ψ|[Ox(t),Oy]|ψ⟩ are negligible in every state |ψ⟩ when |x−y|≳vt, where v is finite when α>3 (Lieb-Robinson light cone); in a typical state |ψ⟩ drawn from the infinite temperature ensemble, v is finite when α>52 (Frobenius light cone); in non-interacting systems, v is finite in every state when α>2 (free light cone). These bounds apply to time-dependent systems and are optimal up to subalgebraic improvements. Our theorems regarding the Lieb-Robinson and free light cones, and their tightness, also generalize to arbitrary dimensions. We discuss the implications of our bounds on the growth of connected correlators and of topological order, the clustering of correlations in gapped systems, and the digital simulation of systems with long-range interactions. In addition, we show that quantum state transfer and many-body quantum chaos are bounded by the Frobenius light cone, and therefore are poorly constrained by all Lieb-Robinson bounds.

1 aTran, Minh, C.1 aChen, Chi-Fang1 aEhrenberg, Adam1 aGuo, Andrew, Y.1 aDeshpande, Abhinav1 aHong, Yifan1 aGong, Zhe-Xuan1 aGorshkov, Alexey, V.1 aLucas, Andrew uhttps://arxiv.org/abs/2001.1150901522nas 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/2008.0607401577nas a2200157 4500008004100000245004200041210004200083260001400125520114200139100001701281700002301298700001801321700002401339700001901363856003701382 2020 eng d00aOptimal control for quantum detectors0 aOptimal control for quantum detectors c5/12/20203 a

Quantum systems are promising candidates for sensing of weak signals as they can provide unrivaled performance when estimating parameters of external fields. However, when trying to detect weak signals that are hidden by background noise, the signal-to-noise-ratio is a more relevant metric than raw sensitivity. We identify, under modest assumptions about the statistical properties of the signal and noise, the optimal quantum control to detect an external signal in the presence of background noise using a quantum sensor. Interestingly, for white background noise, the optimal solution is the simple and well-known spin-locking control scheme. We further generalize, using numerical techniques, these results to the background noise being a correlated Lorentzian spectrum. We show that for increasing correlation time, pulse based sequences such as CPMG are also close to the optimal control for detecting the signal, with the crossover dependent on the signal frequency. These results show that an optimal detection scheme can be easily implemented in near-term quantum sensors without the need for complicated pulse shaping.

1 aTitum, Paraj1 aSchultz, Kevin, M.1 aSeif, Alireza1 aQuiroz, Gregory, D.1 aClader, B., D. uhttps://arxiv.org/abs/2005.0599501333nas a2200157 4500008004100000245008800041210006900129260001400198520082100212100001901033700002301052700002001075700001801095700002501113856003701138 2020 eng d00aOptimal state transfer and entanglement generation in power-law interacting systems0 aOptimal state transfer and entanglement generation in powerlaw i c10/6/20203 a

We present an optimal protocol for encoding an unknown qubit state into a multiqubit Greenberger-Horne-Zeilinger-like state and, consequently, transferring quantum information in large systems exhibiting power-law (1/rα) interactions. For all power-law exponents α between d and 2d+1, where d is the dimension of the system, the protocol yields a polynomial speedup for α>2d and a superpolynomial speedup for α≤2d, compared to the state of the art. For all α>d, the protocol saturates the Lieb-Robinson bounds (up to subpolynomial corrections), thereby establishing the optimality of the protocol and the tightness of the bounds in this regime. The protocol has a wide range of applications, including in quantum sensing, quantum computing, and preparation of topologically ordered states. 

1 aTran, Minh, C.1 aDeshpande, Abhinav1 aGuo, Andrew, Y.1 aLucas, Andrew1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2010.0293001590nas a2200133 4500008004100000245008000041210006900121260001400190520115200204100002501356700001901381700001901400856003701419 2020 eng d00aOptimal Two-Qubit Circuits for Universal Fault-Tolerant Quantum Computation0 aOptimal TwoQubit Circuits for Universal FaultTolerant Quantum Co c1/16/20203 a

We study two-qubit circuits over the Clifford+CS gate set which consists of Clifford gates together with the controlled-phase gate CS=diag(1,1,1,i). The Clifford+CS gate set is universal for quantum computation and its elements can be implemented fault-tolerantly in most error-correcting schemes with magic state distillation. However, since non-Clifford gates are typically more expensive to perform in a fault-tolerant manner, it is desirable to construct circuits that use few CS gates. In the present paper, we introduce an algorithm to construct optimal circuits for two-qubit Clifford+CS operators. Our algorithm inputs a Clifford+CS operator U and efficiently produces a Clifford+CS circuit for U using the least possible number of CS gates. Because our algorithm is deterministic, the circuit it associates to a Clifford+CS operator can be viewed as a normal form for the operator. We give a formal description of these normal forms as walks over certain graphs and use this description to derive an asymptotic lower bound of 5log(1/epsilon)+O(1) on the number CS gates required to epsilon-approximate any 4x4 unitary matrix. 

1 aGlaudell, Andrew, N.1 aRoss, Neil, J.1 aTaylor, J., M. uhttps://arxiv.org/abs/2001.0599702249nas a2200133 4500008004100000245007900041210006900120260001500189520179100204100002401995700001902019700001902038856005802057 2020 eng d00aPosition Space Decoherence From Long-Range Interaction With Background Gas0 aPosition Space Decoherence From LongRange Interaction With Backg c06/05/20203 a

 Experiments in matter wave interferometry and optomechanics are increasing the spatial extent of wavefunctions of massive quantum systems; this gives rise to new sources of decoherence that must be characterized. Here we calculate the position space decoherence of a quantum particle due to interaction with a fluctuating classical background gas for several different force laws. We begin with the calculation of this effect for the Newton potential. To our knowledge, this calculation has not been done before. We then solve the same problem in the case of a Yukawa interaction, which interpolates between our long-range force result and the well-studied formula for collisional decoherence from a contact interaction. Unlike the contact interaction case, where the decoherence rate becomes independent of distance for large quantum particle separations, we observe that a long-range interaction leads to quadratic scaling of the decoherence rate with distance even at large separations. This work is relevant to the generation of massive superposition in optomechanical and atom beam experiments, and to conclude we comment on the use of this decoherence signal for gravitational detection of dark matter. 

1 aKunjummen, Jonathan1 aCarney, Daniel1 aTaylor, J., M. uhttp://meetings.aps.org/Meeting/DAMOP20/Session/S08.501854nas a2200193 4500008004100000245008800041210006900129260001400198520128100212100001501493700001701508700001501525700001601540700001701556700001401573700001901587700001701606856003701623 2020 eng d00aProbing XY phase transitions in a Josephson junction array with tunable frustration0 aProbing XY phase transitions in a Josephson junction array with  c1/22/20203 a

The seminal theoretical works of Berezinskii, Kosterlitz, and Thouless presented a new paradigm for phase transitions in condensed matter that are driven by topological excitations. These transitions have been extensively studied in the context of two-dimensional XY models -- coupled compasses -- and have generated interest in the context of quantum simulation. Here, we use a circuit quantum-electrodynamics architecture to study the critical behavior of engineered XY models through their dynamical response. In particular, we examine not only the unfrustrated case but also the fully-frustrated case which leads to enhanced degeneracy associated with the spin rotational [U(1)] and discrete chiral (Z2) symmetries. The nature of the transition in the frustrated case has posed a challenge for theoretical studies while direct experimental probes remain elusive. Here we identify the transition temperatures for both the unfrustrated and fully-frustrated XY models by probing a Josephson junction array close to equilibrium using weak microwave excitations and measuring the temperature dependence of the effective damping obtained from the complex reflection coefficient. We argue that our probing technique is primarily sensitive to the dynamics of the U(1) part.

1 aCosmic, R.1 aKawabata, K.1 aAshida, Y.1 aIkegami, H.1 aFurukawa, S.1 aPatil, P.1 aTaylor, J., M.1 aNakamura, Y. uhttps://arxiv.org/abs/2001.0787701423nas 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/2010.0050002222nas a2200169 4500008004100000245010800041210006900149260001400218520167700232100001801909700001901927700001701946700001901963700001501982700001801997856003702015 2020 eng d00aSampling-based sublinear low-rank matrix arithmetic framework for dequantizing quantum machine learning0 aSamplingbased sublinear lowrank matrix arithmetic framework for  c6/18/20203 a

We present an algorithmic framework for quantum-inspired classical algorithms on close-to-low-rank matrices, generalizing the series of results started by Tang's breakthrough quantum-inspired algorithm for recommendation systems [STOC'19]. Motivated by quantum linear algebra algorithms and the quantum singular value transformation (SVT) framework of Gilyén et al. [STOC'19], we develop classical algorithms for SVT that run in time independent of input dimension, under suitable quantum-inspired sampling assumptions. Our results give compelling evidence that in the corresponding QRAM data structure input model, quantum SVT does not yield exponential quantum speedups. Since the quantum SVT framework generalizes essentially all known techniques for quantum linear algebra, our results, combined with sampling lemmas from previous work, suffice to generalize all recent results about dequantizing quantum machine learning algorithms. In particular, our classical SVT framework recovers and often improves the dequantization results on recommendation systems, principal component analysis, supervised clustering, support vector machines, low-rank regression, and semidefinite program solving. We also give additional dequantization results on low-rank Hamiltonian simulation and discriminant analysis. Our improvements come from identifying the key feature of the quantum-inspired input model that is at the core of all prior quantum-inspired results: ℓ2-norm sampling can approximate matrix products in time independent of their dimension. We reduce all our main results to this fact, making our exposition concise, self-contained, and intuitive.

1 aChia, Nai-Hui1 aGilyen, Andras1 aLi, Tongyang1 aLin, Han-Hsuan1 aTang, Ewin1 aWang, Chunhao uhttps://arxiv.org/abs/1910.0615101772nas a2200169 4500008004100000245006700041210006600108260001300174490000800187520126400195100002001459700001901479700002301498700002501521700001901546856003701565 2020 eng d00aSignaling and Scrambling with Strongly Long-Range Interactions0 aSignaling and Scrambling with Strongly LongRange Interactions c7/8/20200 v1023 a

Strongly long-range interacting quantum systems---those with interactions decaying as a power-law 1/rα in the distance r on a D-dimensional lattice for α≤D---have received significant interest in recent years. They are present in leading experimental platforms for quantum computation and simulation, as well as in theoretical models of quantum information scrambling and fast entanglement creation. Since no notion of locality is expected in such systems, a general understanding of their dynamics is lacking. As a first step towards rectifying this problem, we prove two new Lieb-Robinson-type bounds that constrain the time for signaling and scrambling in strongly long-range interacting systems, for which no tight bounds were previously known. Our first bound applies to systems mappable to free-particle Hamiltonians with long-range hopping, and is saturable for α≤D/2. Our second bound pertains to generic long-range interacting spin Hamiltonians, and leads to a tight lower bound for the signaling time to extensive subsets of the system for all α<D. This result also lower-bounds the scrambling time, and suggests a path towards achieving a tight scrambling bound that can prove the long-standing fast scrambling conjecture. 

1 aGuo, Andrew, Y.1 aTran, Minh, C.1 aChilds, Andrew, M.1 aGorshkov, Alexey, V.1 aGong, Zhe-Xuan uhttps://arxiv.org/abs/1906.0266201240nas a2200145 4500008004100000245006500041210006400106260001500170520080100185100001800986700001601004700001801020700001901038856003701057 2019 eng d00aBeyond Spontaneous Emission: Giant Atom Bounded in Continuum0 aBeyond Spontaneous Emission Giant Atom Bounded in Continuum c12/20/20193 a

The quantum coupling of individual superconducting qubits to microwave photons leads to remarkable experimental opportunities. Here we consider the phononic case where the qubit is coupled to an electromagnetic surface acoustic wave antenna that enables supersonic propagation of the qubit oscillations. This can be considered as a giant atom that is many phonon wavelengths long. We study an exactly solvable toy model that captures these effects, and find that this non-Markovian giant atom has a suppressed relaxation, as well as an effective vacuum coupling between a qubit excitation and a localized wave packet of sound, even in the absence of a cavity for the sound waves. Finally, we consider practical implementations of these ideas in current surface acoustic wave devices. 

1 aGuo, Shangjie1 aWang, Yidan1 aPurdy, Thomas1 aTaylor, J., M. uhttps://arxiv.org/abs/1912.0998001389nas a2200157 4500008004100000245005900041210005700100260001400157300001000171490000800181520094200189100002501131700001901156700001901175856003701194 2019 eng d00aCanonical forms for single-qutrit Clifford+T operators0 aCanonical forms for singlequtrit CliffordT operators c8/19/2019 a54-700 v4063 a

We introduce canonical forms for single qutrit Clifford+T circuits and prove that every single-qutrit Clifford+T operator admits a unique such canonical form. We show that our canonical forms are T-optimal in the sense that among all the single-qutrit Clifford+T circuits implementing a given operator our canonical form uses the least number of T gates. Finally, we provide an algorithm which inputs the description of an operator (as a matrix or a circuit) and constructs the canonical form for this operator. The algorithm runs in time linear in the number of T gates. Our results provide a higher-dimensional generalization of prior work by Matsumoto and Amano who introduced similar canonical forms for single-qubit Clifford+T circuits. 

1 aGlaudell, Andrew, N.1 aRoss, Neil, J.1 aTaylor, J., M. uhttps://arxiv.org/abs/1803.0504701228nas a2200145 4500008004100000245007500041210006900116260001500185520076500200100002100965700002100986700001901007700001901026856003701045 2019 eng d00aA characterization of quantum chaos by two-point correlation functions0 acharacterization of quantum chaos by twopoint correlation functi c02/28/20193 a

We propose a characterization of quantum many-body chaos: given a collection of simple operators, the set of all possible pair-correlations between these operators can be organized into a matrix with random-matrix-like spectrum. This approach is particularly useful for locally interacting systems, which do not generically show exponential Lyapunov growth of out-of-time-ordered correlators. We demonstrate the validity of this characterization by numerically studying the Sachdev-Ye-Kitaev model and a one-dimensional spin chain with random magnetic field (XXZ model).

1 aGharibyan, Hrant1 aHanada, Masanori1 aSwingle, Brian1 aTezuka, Masaki uhttps://arxiv.org/abs/1902.1108601697nas 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/1810.0236501739nas 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/1912.0487401980nas a2200193 4500008004100000245011000041210006900151260001500220520137500235100001801610700001601628700001401644700001501658700001301673700002501686700002001711700001801731856003701749 2019 eng d00aFloquet engineering of optical lattices with spatial features and periodicity below the diffraction limit0 aFloquet engineering of optical lattices with spatial features an c06/18/20193 a

Floquet engineering or coherent time periodic driving of quantum systems has been successfully used to synthesize Hamiltonians with novel properties. In ultracold atomic systems, this has led to experimental realizations of artificial gauge fields, topological band structures, and observation of dynamical localization, to name just a few. Here we present a Floquet-based framework to stroboscopically engineer Hamiltonians with spatial features and periodicity below the diffraction limit of light used to create them by time-averaging over various configurations of a 1D optical Kronig-Penney (KP) lattice. The KP potential is a lattice of narrow subwavelength barriers spaced by half the optical wavelength (λ/2) and arises from the non-linear optical response of the atomic dark state. Stroboscopic control over the strength and position of this lattice requires time-dependent adiabatic manipulation of the dark state spin composition. We investigate adiabaticity requirements and shape our time-dependent light fields to respect the requirements. We apply this framework to show that a λ/4-spaced lattice can be synthesized using realistic experimental parameters as an example, discuss mechanisms that limit lifetimes in these lattices, explore candidate systems and their limitations, and treat adiabatic loading into the ground band of these lattices.

1 aSubhankar, S.1 aBienias, P.1 aTitum, P.1 aTsui, T-C.1 aWang, Y.1 aGorshkov, Alexey, V.1 aRolston, S., L.1 aPorto, J., V. uhttps://arxiv.org/abs/1906.0764601480nas 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/1904.0322201741nas a2200205 4500008004100000245007000041210006900111260001500180490000600195520112800201100001901329700002001348700001301368700002401381700002201405700002301427700002301450700002501473856003701498 2019 eng d00aLocality and digital quantum simulation of power-law interactions0 aLocality and digital quantum simulation of powerlaw interactions c07/10/20190 v93 a

The propagation of information in non-relativistic quantum systems obeys a speed limit known as a Lieb-Robinson bound. We derive a new Lieb-Robinson bound for systems with interactions that decay with distance r as a power law, 1/rα. The bound implies an effective light cone tighter than all previous bounds. Our approach is based on a technique for approximating the time evolution of a system, which was first introduced as part of a quantum simulation algorithm by Haah et al. [arXiv:1801.03922]. To bound the error of the approximation, we use a known Lieb-Robinson bound that is weaker than the bound we establish. This result brings the analysis full circle, suggesting a deep connection between Lieb-Robinson bounds and digital quantum simulation. In addition to the new Lieb-Robinson bound, our analysis also gives an error bound for the Haah et al. quantum simulation algorithm when used to simulate power-law decaying interactions. In particular, we show that the gate count of the algorithm scales with the system size better than existing algorithms when α>3D (where D is the number of dimensions).

1 aTran, Minh, C.1 aGuo, Andrew, Y.1 aSu, Yuan1 aGarrison, James, R.1 aEldredge, Zachary1 aFoss-Feig, Michael1 aChilds, Andrew, M.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1808.0522501621nas a2200181 4500008004100000245007900041210006900120260001500189490000800204520106600212100001901278700002001297700002001317700001701337700002301354700002501377856003701402 2019 eng d00aLocality and Heating in Periodically Driven, Power-law Interacting Systems0 aLocality and Heating in Periodically Driven Powerlaw Interacting c2019/11/120 v1003 a

We study the heating time in periodically driven D-dimensional systems with interactions that decay with the distance r as a power-law 1/rα. Using linear response theory, we show that the heating time is exponentially long as a function of the drive frequency for α>D. For systems that may not obey linear response theory, we use a more general Magnus-like expansion to show the existence of quasi-conserved observables, which imply exponentially long heating time, for α>2D. We also generalize a number of recent state-of-the-art Lieb-Robinson bounds for power-law systems from two-body interactions to k-body interactions and thereby obtain a longer heating time than previously established in the literature. Additionally, we conjecture that the gap between the results from the linear response theory and the Magnus-like expansion does not have physical implications, but is, rather, due to the lack of tight Lieb-Robinson bounds for power-law interactions. We show that the gap vanishes in the presence of a hypothetical, tight bound. 

1 aTran, Minh, C.1 aEhrenberg, Adam1 aGuo, Andrew, Y.1 aTitum, Paraj1 aAbanin, Dmitry, A.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1908.0277301912nas 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/1912.1111701814nas a2200169 4500008004100000245006700041210006600108260001400174490000800188520130400196100001701500700002201517700002401539700002501563700001901588856003701607 2019 eng d00aProbing ground-state phase transitions through quench dynamics0 aProbing groundstate phase transitions through quench dynamics c9/11/20190 v1233 a

The study of quantum phase transitions requires the preparation of a many-body system near its ground state, a challenging task for many experimental systems. The measurement of quench dynamics, on the other hand, is now a routine practice in most cold atom platforms. Here we show that quintessential ingredients of quantum phase transitions can be probed directly with quench dynamics in integrable and nearly integrable systems. As a paradigmatic example, we study global quench dynamics in a transverse-field Ising model with either short-range or long-range interactions. When the model is integrable, we discover a new dynamical critical point with a non-analytic signature in the short-range correlators. The location of the dynamical critical point matches that of the quantum critical point and can be identified using a finite-time scaling method. We extend this scaling picture to systems near integrability and demonstrate the continued existence of a dynamical critical point detectable at prethermal time scales. Therefore, our method can be used to approximately locate the quantum critical point. The scaling method is also relevant to experiments with finite time and system size, and our predictions are testable in near-term experiments with trapped ions and Rydberg atoms.

1 aTitum, Paraj1 aIosue, Joseph, T.1 aGarrison, James, R.1 aGorshkov, Alexey, V.1 aGong, Zhe-Xuan uhttps://arxiv.org/abs/1809.0637701764nas 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/1911.0712701364nas a2200157 4500008004100000245003000041210003000071260001500101490000800116520096500124100002101089700002101110700001901131700001901150856003701169 2019 eng d00aQuantum Lyapunov Spectrum0 aQuantum Lyapunov Spectrum c04/10/20190 v0823 a

We introduce a simple quantum generalization of the spectrum of classical Lyapunov exponents. We apply it to the SYK and XXZ models, and study the Lyapunov growth and entropy production. Our numerical results suggest that a black hole is not just the fastest scrambler, but also the fastest entropy generator. We also study the statistical features of the quantum Lyapunov spectrum and find universal random matrix behavior, which resembles the recently-found universality in classical chaos. The random matrix behavior is lost when the system is deformed away from chaos, towards integrability or a many-body localized phase. We propose that quantum systems holographically dual to gravity satisfy this universality in a strong form. We further argue that the quantum Lyapunov spectrum contains important additional information beyond the largest Lyapunov exponent and hence provides us with a better characterization of chaos in quantum systems. 

1 aGharibyan, Hrant1 aHanada, Masanori1 aSwingle, Brian1 aTezuka, Masaki uhttps://arxiv.org/abs/1809.0167101653nas a2200169 4500008004100000245007700041210006900118260001500187300001100202490000700213520111300220100002301333700001701356700002501373700001601398856006901414 2018 eng d00aAbsence of Thermalization in Finite Isolated Interacting Floquet Systems0 aAbsence of Thermalization in Finite Isolated Interacting Floquet c2018/01/29 a0143110 v973 a

Conventional wisdom suggests that the long time behavior of isolated interacting periodically driven (Floquet) systems is a featureless maximal entropy state characterized by an infinite temperature. Efforts to thwart this uninteresting fixed point include adding sufficient disorder to realize a Floquet many-body localized phase or working in a narrow region of drive frequencies to achieve glassy non-thermal behavior at long time. Here we show that in clean systems the Floquet eigenstates can exhibit non-thermal behavior due to finite system size. We consider a one-dimensional system of spinless fermions with nearest-neighbor interactions where the interaction term is driven. Interestingly, even with no static component of the interaction, the quasienergy spectrum contains gaps and a significant fraction of the Floquet eigenstates, at all quasienergies, have non-thermal average doublon densities. We show that this non-thermal behavior arises due to emergent integrability at large interaction strength and discuss how the integrability breaks down with power-law behavior in system size.

1 aSeetharam, Karthik1 aTitum, Paraj1 aKolodrubetz, Michael1 aRefael, Gil uhttps://journals.aps.org/prb/abstract/10.1103/PhysRevB.97.01431101252nas a2200133 4500008004100000245006000041210005600101260001500157520084400172100002201016700002401038700001901062856003701081 2018 eng d00aAn autonomous single-piston engine with a quantum rotor0 aautonomous singlepiston engine with a quantum rotor c2018/02/153 a

Pistons are elementary components of a wide variety of thermal engines, converting input fuel into rotational motion. Here, we propose a single-piston engine where the rotational degree of freedom is effectively realized by the flux of a superconducting island -- a quantum rotor -- while the working volume corresponds to the effective length of a superconducting resonator. Our autonomous design implements a Carnot cycle, relies solely on standard thermal baths and can be implemented with circuit quantum electrodynamics. We demonstrate how the piston is able to extract a net positive work via its built-in synchronicity using a filter cavity as an effective valve, eliminating the need for external control.

1 aRoulet, Alexandre1 aNimmrichter, Stefan1 aTaylor, J., M. uhttps://arxiv.org/abs/1802.0548601296nas 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/1801.0307101515nas a2200121 4500008004100000245006500041210006500106260001500171520113200186100001901318700001901337856003701356 2018 eng d00aBlind quantum computation using the central spin Hamiltonian0 aBlind quantum computation using the central spin Hamiltonian c2018/01/113 a

Blindness is a desirable feature in delegated computation. In the classical setting, blind computations protect the data or even the program run by a server. In the quantum regime, blind computing may also enable testing computational or other quantum properties of the server system. Here we propose a scheme for universal blind quantum computation using a quantum simulator capable of emulating Heisenberg-like Hamiltonians. Our scheme is inspired by the central spin Hamiltonian in which a single spin controls dynamics of a number of bath spins. We show how, by manipulating this spin, a client that only accesses the central spin can effectively perform blind computation on the bath spins. Remarkably, two-way quantum communication mediated by the central spin is sufficient to ensure security in the scheme. Finally, we provide explicit examples of how our universal blind quantum computation enables verification of the power of the server from classical to stabilizer to full BQP computation.

1 aTran, Minh, C.1 aTaylor, J., M. uhttps://arxiv.org/abs/1801.0400601390nas a2200145 4500008004100000245007200041210006900113520091900182100002201101700002101123700001801144700002601162700001901188856003701207 2018 eng d00aBose Condensation of Photons Thermalized via Laser Cooling of Atoms0 aBose Condensation of Photons Thermalized via Laser Cooling of At3 a

A Bose-Einstein condensate (BEC) is a quantum phase of matter achieved at low temperatures. Photons, one of the most prominent species of bosons, do not typically condense due to the lack of a particle number-conservation. We recently described a photon thermalization mechanism which gives rise to a grand canonical ensemble of light with effective photon number conservation between a subsystem and a particle reservoir. This mechanism occurs during Doppler laser cooling of atoms where the atoms serve as a temperature reservoir while the cooling laser photons serve as a particle reservoir. Here we address the question of the possibility of a BEC of photons in this laser cooling photon thermalization scenario and theoretically demonstrate that a Bose condensation of photons can be realized by cooling an ensemble of two-level atoms (realizable with alkaline earth atoms) inside a Fabry-Perot cavity.

1 aWang, Chiao-Hsuan1 aGullans, Michael1 aPorto, J., V.1 aPhillips, William, D.1 aTaylor, J., M. uhttps://arxiv.org/abs/1809.0777705095nas a2200169 4500008004100000245007900041210006900120260001500189520455700204100001804761700001804779700001804797700002004815700001704835700001604852856005704868 2018 eng d00aCapacity Approaching Codes for Low Noise Interactive Quantum Communication0 aCapacity Approaching Codes for Low Noise Interactive Quantum Com c2018/01/013 a
We consider the problem of implementing two-party interactive quantum
communication over noisy channels, a necessary endeavor if we wish to
fully reap quantum advantages for communication.  
 
For an arbitrary protocol with n messages, designed for
noiseless qudit channels, our main result is a simulation method that fails with probability less than
$2^{-\Theta(n\epsilon)}$ and uses a qudit channel $n(1 + \Theta
(\sqrt{\epsilon}))$ times, of which an $\epsilon$ fraction can be
corrupted adversarially.
 
The simulation is thus capacity achieving to leading order, and
we conjecture that it is optimal up to a constant factor in 
the $\sqrt{\epsilon}$ term.  
 
Furthermore, the simulation is in a model that does not require
pre-shared resources such as randomness or entanglement between the
communicating parties.
 
Surprisingly, this outperforms the best-known overhead of $1 +
O(\sqrt{\epsilon \log \log 1/\epsilon})$ in the corresponding
\emph{classical} model, which is also conjectured to be optimal
     [Haeupler, FOCS'14].
 
Our work also improves over the best previously known quantum result
where the overhead is a non-explicit large constant [Brassard \emph{et
    al.}, FOCS'14] for low $\epsilon$.
1 aLeung, Debbie1 aNayak, Ashwin1 aShayeghi, Ala1 aTouchette, Dave1 aYao, Penghui1 aYu, Nengkun uhttp://acm-stoc.org/stoc2018/STOC-2018-Accepted.html01718nas a2200169 4500008004100000245008800041210006900129260001500198520118200213100001501395700002001410700001701430700002201447700001901469700002301488856003701511 2018 eng d00aCircuit QED-based measurement of vortex lattice order in a Josephson junction array0 aCircuit QEDbased measurement of vortex lattice order in a Joseph c2018/03/123 a

Superconductivity provides a canonical example of a quantum phase of matter. When superconducting islands are connected by Josephson junctions in a lattice, the low temperature state of the system can map to the celebrated XY model and its associated universality classes. This has been used to experimentally implement realizations of Mott insulator and Berezinskii--Kosterlitz--Thouless (BKT) transitions to vortex dynamics analogous to those in type-II superconductors. When an external magnetic field is added, the effective spins of the XY model become frustrated, leading to the formation of topological defects (vortices). Here we observe the many-body dynamics of such an array, including frustration, via its coupling to a superconducting microwave cavity. We take the design of the transmon qubit, but replace the single junction between two antenna pads with the complete array. This allows us to probe the system at 10 mK with minimal self-heating by using weak coherent states at the single (microwave) photon level to probe the resonance frequency of the cavity. We observe signatures of ordered vortex lattice at rational flux fillings of the array. 

1 aCosmic, R.1 aIkegami, Hiroki1 aLin, Zhirong1 aInomata, Kunihiro1 aTaylor, J., M.1 aNakamura, Yasunobu uhttps://arxiv.org/abs/1803.0411301379nas a2200217 4500008004100000245005600041210005400097520077800151100001600929700001800945700001300963700001400976700002200990700001501012700002001027700001401047700002001061700001801081700002501099856003701124 2018 eng d00aCoherent optical nano-tweezers for ultra-cold atoms0 aCoherent optical nanotweezers for ultracold atoms3 a

There has been a recent surge of interest and progress in creating subwavelength free-space optical potentials for ultra-cold atoms. A key open question is whether geometric potentials, which are repulsive and ubiquitous in the creation of subwavelength free-space potentials, forbid the creation of narrow traps with long lifetimes. Here, we show that it is possible to create such traps. We propose two schemes for realizing subwavelength traps and demonstrate their superiority over existing proposals. We analyze the lifetime of atoms in such traps and show that long-lived bound states are possible. This work opens a new frontier for the subwavelength control and manipulation of ultracold matter, with applications in quantum chemistry and quantum simulation.

1 aBienias, P.1 aSubhankar, S.1 aWang, Y.1 aTsui, T-C1 aJendrzejewski, F.1 aTiecke, T.1 aJuzeliūnas, G.1 aJiang, L.1 aRolston, S., L.1 aPorto, J., V.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1808.0248701523nas 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/1802.0311804213nas a2200241 4500008004100000245006900041210006800110260001500178300001100193490000800204520348600212100001503698700002303713700002403736700001903760700001903779700002503798700002503823700001803848700002103866700002403887856006003911 2018 eng d00aDark state optical lattice with sub-wavelength spatial structure0 aDark state optical lattice with subwavelength spatial structure c2018/02/20 a0836010 v1203 a

We report on the experimental realization of a conservative optical lattice for cold atoms with a subwavelength spatial structure. The potential is based on the nonlinear optical response of three-level atoms in laser-dressed dark states, which is not constrained by the diffraction limit of the light generating the potential. The lattice consists of a one-dimensional array of ultranarrow barriers with widths less than 10 nm, well below the wavelength of the lattice light, physically realizing a Kronig-Penney potential. We study the band structure and dissipation of this lattice and find good agreement with theoretical predictions. Even on resonance, the observed lifetimes of atoms trapped in the lattice are as long as 44 ms, nearly 105times the excited state lifetime, and could be further improved with more laser intensity. The potential is readily generalizable to higher dimensions and different geometries, allowing, for example, nearly perfect box traps, narrow tunnel junctions for atomtronics applications, and dynamically generated lattices with subwavelength spacings.

1 aWang, Yang1 aSubhankar, Sarthak1 aBienias, Przemyslaw1 aLacki, Mateusz1 aTsui, Tsz-Chun1 aBaranov, Mikhail, A.1 aGorshkov, Alexey, V.1 aZoller, Peter1 aPorto, James, V.1 aRolston, Steven, L. uhttps://link.aps.org/doi/10.1103/PhysRevLett.120.08360101943nas a2200121 4500008004100000245007800041210006900119520154200188100001801730700001901748700001701767856003701784 2018 eng d00aDynamic suppression of Rayleigh light scattering in dielectric resonators0 aDynamic suppression of Rayleigh light scattering in dielectric r3 a

The ultimate limits of performance for any classical optical system are set by sub-wavelength fluctuations within the host material, that may be frozen-in or even dynamically induced. The most common manifestation of such sub-wavelength disorder is Rayleigh light scattering, which is observed in nearly all wave-guiding technologies today and can lead to both irreversible radiative losses as well as undesirable intermodal coupling. While it has been shown that backscattering from disorder can be suppressed by breaking time-reversal symmetry in magneto-optic and topological insulator materials, common optical dielectrics possess neither of these properties. Here we demonstrate an optomechanical approach for dynamically suppressing Rayleigh backscattering within dielectric resonators. We achieve this by locally breaking time-reversal symmetry in a silica resonator through a Brillouin scattering interaction that is available in all materials. Near-complete suppression of Rayleigh backscattering is experimentally confirmed through three independent measurements -- the reduction of the back-reflections caused by scatterers, the elimination of a commonly seen normal-mode splitting effect, and by measurement of the reduction in intrinsic optical loss. More broadly, our results provide new evidence that it is possible to dynamically suppress Rayleigh backscattering within any optical dielectric medium, for achieving robust light propagation in nanophotonic devices in spite of the presence of scatterers or defects.

1 aKim, Seunghwi1 aTaylor, J., M.1 aBahl, Gaurav uhttps://arxiv.org/abs/1803.0236612409nas a2200169 45000080041000002450055000412100055000963000047001514900008001985201188600206100002312092700002012115700001912135700002312154700002512177856003712202 2018 eng d00aDynamical phase transitions in sampling complexity0 aDynamical phase transitions in sampling complexity a12 pages, 4 figures. v3: published version0 v1213 a

We make the case for studying the complexity of approximately simulating (sampling) quantum systems for reasons beyond that of quantum computational supremacy, such as diagnosing phase transitions. We consider the sampling complexity as a function of time t due to evolution generated by spatially local quadratic bosonic Hamiltonians. We obtain an upper bound on the scaling of t with the number of bosons n for which approximate sampling is classically efficient. We also obtain a lower bound on the scaling of t with n for which any instance of the boson sampling problem reduces to this problem and hence implies that the problem is hard, assuming the conjectures of Aaronson and Arkhipov [Proc. 43rd Annu. ACM Symp. Theory Comput. STOC '11]. This establishes a dynamical phase transition in sampling complexity. Further, we show that systems in the Anderson-localized phase are always easy to sample from at arbitrarily long times. We view these results in the light of classifying phases of physical systems based on parameters in the Hamiltonian. In doing so, we combine ideas from mathematical physics and computational complexity to gain insight into the behavior of condensed matter, atomic, molecular and optical systems.

1 aDeshpande, Abhinav1 aFefferman, Bill1 aTran, Minh, C.1 aFoss-Feig, Michael1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1703.0533201662nas a2200217 4500008004100000245004200041210004000083260001500123300001200138490000600150520105500156100002101211700002201232700002101254700002201275700002301297700001601320700001901336700001601355856007301371 2018 eng d00aElectro-mechano-optical NMR detection0 aElectromechanooptical NMR detection c2018/02/01 a152-1580 v53 a

Signal reception of nuclear magnetic resonance (NMR) usually relies on electrical amplification of the electromotive force caused by nuclear induction. Here, we report up-conversion of a radio-frequency NMR signal to an optical regime using a high-stress silicon nitride membrane that interfaces the electrical detection circuit and an optical cavity through the electro-mechanical and the opto-mechanical couplings. This enables optical NMR detection without sacrificing the versatility of the traditional nuclear induction approach. While the signal-to-noise ratio is currently limited by the Brownian motion of the membrane as well as additional technical noise, we find it can exceed that of the conventional electrical schemes by increasing the electro-mechanical coupling strength. The electro-mechano-optical NMR detection presented here can even be combined with the laser cooling technique applied to nuclear spins.

1 aTakeda, Kazuyuki1 aNagasaka, Kentaro1 aNoguchi, Atsushi1 aYamazaki, Rekishu1 aNakamura, Yasunobu1 aIwase, Eiji1 aTaylor, J., M.1 aUsami, Koji uhttps://www.osapublishing.org/optica/abstract.cfm?uri=optica-5-2-15202284nas a2200145 4500008004100000245007200041210006900113260001500182520181800197100001802015700002302033700001902056700002602075856003702101 2018 eng d00aElectro-optomechanical equivalent circuits for quantum transduction0 aElectrooptomechanical equivalent circuits for quantum transducti c2018/10/153 a

Using the techniques of optomechanics, a high-Q mechanical oscillator may serve as a link between electromagnetic modes of vastly different frequencies. This approach has successfully been exploited for the frequency conversion of classical signals and has the potential of performing quantum state transfer between superconducting circuitry and a traveling optical signal. Such transducers are often operated in a linear regime, where the hybrid system can be described using linear response theory based on the Heisenberg-Langevin equations. While mathematically straightforward to solve, this approach yields little intuition about the dynamics of the hybrid system to aid the optimization of the transducer. As an analysis and design tool for such electro-optomechanical transducers, we introduce an equivalent circuit formalism, where the entire transducer is represented by an electrical circuit. Thereby we integrate the transduction functionality of optomechanical (OM) systems into the toolbox of electrical engineering allowing the use of its well-established design techniques. This unifying impedance description can be applied both for static (DC) and harmonically varying (AC) drive fields, accommodates arbitrary linear circuits, and is not restricted to the resolved-sideband regime. Furthermore, by establishing the quantized input/output formalism for the equivalent circuit, we obtain the scattering matrix for linear transducers using circuit analysis, and thereby have a complete quantum mechanical characterization of the transducer. Hence, this mapping of the entire transducer to the language of electrical engineering both sheds light on how the transducer performs and can at the same time be used to optimize its performance by aiding the design of a suitable electrical circuit.

1 aZeuthen, Emil1 aSchliesser, Albert1 aTaylor, J., M.1 aSørensen, Anders, S. uhttps://arxiv.org/abs/1710.1013601867nas a2200157 4500008004100000245008200041210006900123260001500192300001100207490000600218520138400224100001701608700002201625700002501647856003701672 2018 eng d00aEnergy-level statistics in strongly disordered systems with power-law hopping0 aEnergylevel statistics in strongly disordered systems with power c2018/07/16 a0142010 vB3 a

Motivated by neutral excitations in disordered electronic materials and systems of trapped ultracold particles with long-range interactions, we study energy-level statistics of quasiparticles with the power-law hopping Hamiltonian ∝1/rα in a strong random potential. In solid-state systems such quasiparticles, which are exemplified by neutral dipolar excitations, lead to long-range correlations of local observables and may dominate energy transport. Focussing on the excitations in disordered electronic systems, we compute the energy-level correlation function R2(ω) in a finite system in the limit of sufficiently strong disorder. At small energy differences the correlations exhibit Wigner-Dyson statistics. In particular, in the limit of very strong disorder the energy-level correlation function is given by R2(ω,V)=A3ωωV for small frequencies ω≪ωV and R2(ω,V)=1−(α−d)A1(ωVω)dα−A2(ωVω)2 for large frequencies ω≫ωV, where ωV∝V−αd is the characteristic matrix element of excitation hopping in a system of volume V, and A1, A2 and A3 are coefficient of order unity which depend on the shape of the system. The energy-level correlation function, which we study, allows for a direct experimental observation, for example, by measuring the correlations of the ac conductance of the system at different frequencies.

1 aTitum, Paraj1 aQuito, Victor, L.1 aSyzranov, Sergey, V. uhttps://arxiv.org/abs/1803.1117801691nas 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/1802.0958602685nas a2200205 4500008004100000245006300041210006100104260001500165300001100180490000700191520207900198100002102277700001802298700002202316700001602338700001902354700001802373700001902391856006902410 2018 eng d00aHigh-fidelity quantum gates in Si/SiGe double quantum dots0 aHighfidelity quantum gates in SiSiGe double quantum dots c2018/02/15 a0854210 v973 a

Motivated by recent experiments of Zajac et al. [Science 359, 439 (2018)], we theoretically describe high-fidelity two-qubit gates using the exchange interaction between the spins in neighboring quantum dots subject to a magnetic field gradient. We use a combination of analytical calculations and numerical simulations to provide the optimal pulse sequences and parameter settings for the gate operation. We present a synchronization method which avoids detrimental spin flips during the gate operation and provide details about phase mismatches accumulated during the two-qubit gates which occur due to residual exchange interaction, nonadiabatic pulses, and off-resonant driving. By adjusting the gate times, synchronizing the resonant and off-resonant transitions, and compensating these phase mismatches by phase control, the overall gate fidelity can be increased significantly.

1 aRuss, Maximilian1 aZajac, D., M.1 aSigillito, A., J.1 aBorjans, F.1 aTaylor, J., M.1 aPetta, J., R.1 aBurkard, Guido uhttps://journals.aps.org/prb/abstract/10.1103/PhysRevB.97.08542101444nas a2200169 4500008004100000245007500041210006900116260001500185490000600200520093200206100001701138700002201155700001901177700001901196700002201215856003701237 2018 eng d00aObservation of bound state self-interaction in a nano-eV atom collider0 aObservation of bound state selfinteraction in a nanoeV atom coll c2018/11/200 v93 a

Quantum mechanical scattering resonances for colliding particles occur when a continuum scattering state couples to a discrete bound state between them. The coupling also causes the bound state to interact with itself via the continuum and leads to a shift in the bound state energy, but, lacking knowledge of the bare bound state energy, measuring this self-energy via the resonance position has remained elusive. Here, we report on the direct observation of self-interaction by using a nano-eV atom collider to track the position of a magnetically-tunable Feshbach resonance through a parameter space spanned by energy and magnetic field. Our system of potassium and rubidium atoms displays a strongly non-monotonic resonance trajectory with an exceptionally large self-interaction energy arising from an interplay between the Feshbach bound state and a different, virtual bound state at a fixed energy near threshold.

1 aThomas, Ryan1 aChilcott, Matthew1 aTiesinga, Eite1 aDeb, Amita, B.1 aKjærgaard, Niels uhttps://arxiv.org/abs/1807.0117402023nas a2200241 4500008004100000245007500041210006900116260001500185300001200200490000800212520128400220100001701504700002901521700002201550700002601572700002101598700002501619700002301644700001601667700002301683700002001706856005501726 2018 eng d00aObservation of three-photon bound states in a quantum nonlinear medium0 aObservation of threephoton bound states in a quantum nonlinear m c2018/02/16 a783-7860 v3593 a

Bound states of massive particles, such as nuclei, atoms or molecules, are ubiquitous in nature and constitute the bulk of the visible world around us. In contrast, photons typically only weakly influence each other due to their very weak interactions and vanishing mass. We report the observation of traveling three-photon bound states in a quantum nonlinear medium where the interactions between photons are mediated by atomic Rydberg states. In particular, photon correlation and conditional phase measurements reveal the distinct features associated with three-photon and two-photon bound states. Such photonic trimers and dimers can be viewed as quantum solitons with shape-preserving wavefunctions that depend on the constituent photon number. The observed bunching and strongly nonlinear optical phase are quantitatively described by an effective field theory (EFT) of Rydberg-induced photon-photon interactions, which demonstrates the presence of a substantial effective three-body force between the photons. These observations pave the way towards the realization, studies, and control of strongly interacting quantum many-body states of light.

1 aLiang, Qi-Yu1 aVenkatramani, Aditya, V.1 aCantu, Sergio, H.1 aNicholson, Travis, L.1 aGullans, Michael1 aGorshkov, Alexey, V.1 aThompson, Jeff, D.1 aChin, Cheng1 aLukin, Mikhail, D.1 aVuletic, Vladan uhttp://science.sciencemag.org/content/359/6377/78301354nas a2200121 4500008004100000245009100041210006900132260001500201520093800216100002201154700001901176856003701195 2018 eng d00aOptomechanical approach to controlling the temperature and chemical potential of light0 aOptomechanical approach to controlling the temperature and chemi c2018/05/183 a

Massless particles, including photons, are not conserved even at low energies and thus have no chemical potential. However, in driven systems, near equilibrium dynamics can lead to equilibration of photons with a finite number, describable using an effective chemical potential. Here we build upon this general concept with an implementation appropriate for a nonlinear photon-based quantum simulator. We consider how laser cooling of a well-isolated mechanical mode can provide an effective low-frequency bath for the quantum simulator system. We show that the use of auxiliary photon modes, coupled by the mechanical system, enables control of both the chemical potential, by drive frequency, and temperature, by drive amplitude, of the resulting photonic quantum simulator's grand canonical ensemble.

1 aWang, Chiao-Hsuan1 aTaylor, J., M. uhttps://arxiv.org/abs/1706.0078901661nas a2200121 4500008004100000245009700041210006900138520123700207100001301444700001901457700002601476856003701502 2018 eng d00aOrbital quantum magnetism in spin dynamics of strongly interacting magnetic lanthanide atoms0 aOrbital quantum magnetism in spin dynamics of strongly interacti3 a

Laser cooled lanthanide atoms are ideal candidates with which to study strong and unconventional quantum magnetism with exotic phases. Here, we use state-of-the-art closed-coupling simulations to model quantum magnetism for pairs of ultracold spin-6 erbium lanthanide atoms placed in a deep optical lattice. In contrast to the widely used single-channel Hubbard model description of atoms and molecules in an optical lattice, we focus on the single-site multi-channel spin evolution due to spin-dependent contact, anisotropic van der Waals, and dipolar forces. This has allowed us to identify the leading mechanism, orbital anisotropy, that governs molecular spin dynamics among erbium atoms. The large magnetic moment and combined orbital angular momentum of the 4f-shell electrons are responsible for these strong anisotropic interactions and unconventional quantum magnetism. Multi-channel simulations of magnetic Cr atoms under similar trapping conditions show that their spin-evolution is controlled by spin-dependent contact interactions that are distinct in nature from the orbital anisotropy in Er. The role of an external magnetic field and the aspect ratio of the lattice site on spin dynamics is also investigated.

1 aLi, Ming1 aTiesinga, Eite1 aKotochigova, Svetlana uhttps://arxiv.org/abs/1804.1010202076nas 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/1710.1004701932nas a2200157 4500008004100000245005300041210005300094260000900147520147500156100002201631700002101653700001801674700002601692700001901718856003701737 2018 eng d00aPhoton thermalization via laser cooling of atoms0 aPhoton thermalization via laser cooling of atoms c20183 a

Laser cooling of atomic motion enables a wide variety of technological and scientific explorations using cold atoms. Here we focus on the effect of laser cooling on the photons instead of on the atoms. Specifically, we show that non-interacting photons can thermalize with the atoms to a grand canonical ensemble with a non-zero chemical potential. This thermalization is accomplished via scattering of light between different optical modes, mediated by the laser cooling process. While optically thin modes lead to traditional laser cooling of the atoms, the dynamics of multiple scattering in optically thick modes has been more challenging to describe. We find that in an appropriate set of limits, multiple scattering leads to thermalization of the light with the atomic motion in a manner that approximately conserves total photon number between the laser beams and optically thick modes. In this regime, the subsystem corresponding to the thermalized modes is describable by a grand canonical ensemble with a chemical potential set by the energy of a single laser photon. We consider realization of this regime using two-level atoms in Doppler cooling, and find physically realistic conditions for rare earth atoms. With the addition of photon-photon interactions, this system could provide a new platform for exploring many-body physics.

1 aWang, Chiao-Hsuan1 aGullans, Michael1 aPorto, J., V.1 aPhillips, William, D.1 aTaylor, J., M. uhttps://arxiv.org/abs/1712.0864301748nas a2200157 4500008004100000245010900041210006900150260001500219300001100234490000700245520121100252100002101463700001901484700001801503856006901521 2018 eng d00aProbing electron-phonon interactions in the charge-photon dynamics of cavity-coupled double quantum dots0 aProbing electronphonon interactions in the chargephoton dynamics c2018/01/16 a0353050 v973 a

Electron-phonon coupling is known to play an important role in the charge dynamics of semiconductor quantum dots. Here we explore its role in the combined charge-photon dynamics of cavity-coupled double quantum dots. Previous work on these systems has shown that strong electron-phonon coupling leads to a large contribution to photoemission and gain from phonon-assisted emission and absorption processes. We compare the effects of this phonon sideband in three commonly investigated gate-defined quantum dot material systems: InAs nanowires and GaAs and Si two-dimensional electron gases (2DEGs). We compare our theory with existing experimental data from cavity-coupled InAs nanowire and GaAs 2DEG double quantum dots and find quantitative agreement only when the phonon sideband and photoemission processes during lead tunneling are taken into account. Finally, we show that the phonon sideband also leads to a sizable renormalization of the cavity frequency, which allows for direct spectroscopic probes of the electron-phonon coupling in these systems.

1 aGullans, Michael1 aTaylor, J., M.1 aPetta, J., R. uhttps://journals.aps.org/prb/abstract/10.1103/PhysRevB.97.03530502679nas a2200181 4500008004100000245010000041210006900141260000900210300001300219490000700232520211600239100002402355700002602379700001602405700002002421700001902441856003702460 2018 eng d00aQFlow lite dataset: A machine-learning approach to the charge states in quantum dot experiments0 aQFlow lite dataset A machinelearning approach to the charge stat c2018 ae02058440 v133 a

Over the past decade, machine learning techniques have revolutionized how research is done, from designing new materials and predicting their properties to assisting drug discovery to advancing cybersecurity. Recently, we added to this list by showing how a machine learning algorithm (a so-called learner) combined with an optimization routine can assist experimental efforts in the realm of tuning semiconductor quantum dot (QD) devices. Among other applications, semiconductor QDs are a candidate system for building quantum computers. The present-day tuning techniques for bringing the QD devices into a desirable configuration suitable for quantum computing that rely on heuristics do not scale with the increasing size of the quantum dot arrays required for even near-term quantum computing demonstrations. Establishing a reliable protocol for tuning that does not rely on the gross-scale heuristics developed by experimentalists is thus of great importance. To implement the machine learning-based approach, we constructed a dataset of simulated QD device characteristics, such as the conductance and the charge sensor response versus the applied electrostatic gate voltages. Here, we describe the methodology for generating the dataset, as well as its validation in training convolutional neural networks. We show that the learner's accuracy in recognizing the state of a device is ~96.5 % in both current- and charge-sensor-based training. We also introduce a tool that enables other researchers to use this approach for further research: QFlow lite - a Python-based mini-software suite that uses the dataset to train neural networks to recognize the state of a device and differentiate between states in experimental data. This work gives the definitive reference for the new dataset that will help enable researchers to use it in their experiments or to develop new machine learning approaches and concepts

1 aZwolak, Justyna, P.1 aKalantre, Sandesh, S.1 aWu, Xingyao1 aRagole, Stephen1 aTaylor, J., M. uhttps://arxiv.org/abs/1809.1001801663nas a2200133 4500008004100000245007200041210006900113520124300182100001401425700001401439700002201453700001701475856003701492 2018 eng d00aQuantum Channel Simulation and the Channel's Smooth Max-Information0 aQuantum Channel Simulation and the Channels Smooth MaxInformatio3 a

We study the general framework of quantum channel simulation, that is, the ability of a quantum channel to simulate another one using different classes of codes. First, we show that the minimum error of simulation and the one-shot quantum simulation cost under no-signalling assisted codes are given by semidefinite programs. Second, we introduce the channel's smooth max-information, which can be seen as a one-shot generalization of the mutual information of a quantum channel. We provide an exact operational interpretation of the channel's smooth max-information as the one-shot quantum simulation cost under no-signalling assisted codes. Third, we derive the asymptotic equipartition property of the channel's smooth max-information, i.e., it converges to the quantum mutual information of the channel in the independent and identically distributed asymptotic limit. This implies the quantum reverse Shannon theorem in the presence of no-signalling correlations. Finally, we explore the simulation cost of various quantum channels.

1 aFang, Kun1 aWang, Xin1 aTomamichel, Marco1 aBerta, Mario uhttps://arxiv.org/abs/1807.0535401439nas a2200205 4500008004100000245005100041210005100092260001500143300001200158490000800170520087500178100001801053700002201071700001301093700001601106700001901122700001901141700001801160856005501178 2018 eng d00aResonantly driven CNOT gate for electron spins0 aResonantly driven CNOT gate for electron spins c2018/01/26 a439-4420 v3593 a

Single-qubit rotations and two-qubit CNOT operations are crucial ingredients for universal quantum computing. Although high-fidelity single-qubit operations have been achieved using the electron spin degree of freedom, realizing a robust CNOT gate has been challenging because of rapid nuclear spin dephasing and charge noise. We demonstrate an efficient resonantly driven CNOT gate for electron spins in silicon. Our platform achieves single-qubit rotations with fidelities greater than 99%, as verified by randomized benchmarking. Gate control of the exchange coupling allows a quantum CNOT gate to be implemented with resonant driving in ~200 nanoseconds. We used the CNOT gate to generate a Bell state with 78% fidelity (corrected for errors in state preparation and measurement). Our quantum dot device architecture enables multi-qubit algorithms in silicon.

1 aZajac, D., M.1 aSigillito, A., J.1 aRuss, M.1 aBorjans, F.1 aTaylor, J., M.1 aBurkard, Guido1 aPetta, J., R. uhttp://science.sciencemag.org/content/359/6374/43901174nas 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/1803.0512202029nas a2200205 4500008004100000245009100041210006900132490000900201520141200210100001901622700002001641700001801661700001701679700002001696700002001716700001601736700001701752700001701769856003701786 2018 eng d00aA spinor Bose-Einstein condensate phase-sensitive amplifier for SU(1,1) interferometry0 aspinor BoseEinstein condensate phasesensitive amplifier for SU110 vA 983 a

The SU(1,1) interferometer was originally conceived as a Mach-Zehnder interferometer with the beam-splitters replaced by parametric amplifiers. The parametric amplifiers produce states with correlations that result in enhanced phase sensitivity. F=1 spinor Bose-Einstein condensates (BECs) can serve as the parametric amplifiers for an atomic version of such an interferometer by collisionally producing entangled pairs of ⟨F=1,m=±1| atoms. We simulate the effect of single and double-sided seeding of the inputs to the amplifier using the truncated-Wigner approximation. We find that single-sided seeding degrades the performance of the interferometer exactly at the phase the unseeded interferometer should operate the best. Double-sided seeding results in a phase-sensitive amplifier, where the maximal sensitivity is a function of the phase relationship between the input states of the amplifier. In both single and double-sided seeding we find there exists an optimal phase shift that achieves sensitivity beyond the standard quantum limit. Experimentally, we demonstrate a spinor phase-sensitive amplifier using a BEC of 23Na in an optical dipole trap. This configuration could be used as an input to such an interferometer. We are able to control the initial phase of the double-seeded amplifier, and demonstrate sensitivity to initial population fractions as small as 0.1\%. 

1 aWrubel, J., P.1 aSchwettmann, A.1 aFahey, D., P.1 aGlassman, Z.1 aPechkis, H., K.1 aGriffin, P., F.1 aBarnett, R.1 aTiesinga, E.1 aLett, P., D. uhttps://arxiv.org/abs/1807.0667601154nas a2200121 4500008004100000245006200041210006000103520076900163100001900932700002500951700001900976856003700995 2018 eng d00aTabletop experiments for quantum gravity: a user's manual0 aTabletop experiments for quantum gravity a users manual3 a

Recent advances in cooling, control, and measurement of mechanical systems in the quantum regime have opened the possibility of the first direct observation of quantum gravity, at scales achievable in experiments. This paper gives a broad overview of this idea, using some matter-wave and optomechanical systems to illustrate the predictions of a variety of models of low-energy quantum gravity. We first review the treatment of perturbatively quantized general relativity as an effective quantum field theory, and consider the particular challenges of observing quantum effects in this framework. We then move on to a variety of alternative models, such as those in which gravity is classical, emergent, or responsible for a breakdown of quantum mechanics.

1 aCarney, Daniel1 aStamp, Philip, C. E.1 aTaylor, J., M. uhttps://arxiv.org/abs/1807.1149401154nas a2200121 4500008004100000245006200041210006000103520076900163100001900932700002500951700001900976856003700995 2018 eng d00aTabletop experiments for quantum gravity: a user's manual0 aTabletop experiments for quantum gravity a users manual3 a

Recent advances in cooling, control, and measurement of mechanical systems in the quantum regime have opened the possibility of the first direct observation of quantum gravity, at scales achievable in experiments. This paper gives a broad overview of this idea, using some matter-wave and optomechanical systems to illustrate the predictions of a variety of models of low-energy quantum gravity. We first review the treatment of perturbatively quantized general relativity as an effective quantum field theory, and consider the particular challenges of observing quantum effects in this framework. We then move on to a variety of alternative models, such as those in which gravity is classical, emergent, or responsible for a breakdown of quantum mechanics.

1 aCarney, Daniel1 aStamp, Philip, C. E.1 aTaylor, J., M. uhttps://arxiv.org/abs/1807.1149401813nas a2200169 4500008004100000245010100041210006900142260001500211490000600226520127000232100002701502700001701529700001901546700001901565700002201584856003701606 2017 eng d00aAbove threshold scattering about a Feshbach resonance for ultracold atoms in an optical collider0 aAbove threshold scattering about a Feshbach resonance for ultrac c2017/09/060 v83 a

Studies of magnetically tunable Feshbach resonances in ultracold atomic gases have predominantly been carried out in the zero collision-energy limit. Here, we explore above threshold collisions at well-defined energies in the vicinity of a narrow magnetic Feshbach resonance by means of a laser-based collider. Our experiment focuses on collisions between ground-state 87Rb atoms in the |F = 2,mF = 0i and |F = 1,mF = 1i hyperfine states, which have a known s-wave resonance at 9.040(7) G at threshold that strongly couples to inelastic channels, where 1 G = 10−4 T. Using our collider we can track the magnetic field shift in resonance position as the energy is tuned. This presents a challenge due to the narrow width of the resonance in conjunction with inherent broadening mechanisms of the collider. We find, however, that the narrow Feshbach scattering feature becomes imprinted on the spatial distribution of atoms in a fashion that allows for an accurate determination of resonance position as a function of collision energy through a shift in center-of-mass position of the outgoing clouds. This shift has a dispersive line shape with a zero value at the resonance position. We obtain excellent agreement with theory on the resonance position.

1 aHorvath, Milena, S. J.1 aThomas, Ryan1 aTiesinga, Eite1 aDeb, Amita, B.1 aKjærgaard, Niels uhttps://arxiv.org/abs/1704.0710901776nas a2200145 4500008004100000245004700041210004700088260000900135300001200144520137700156100001901533700001901552700002201571856003701593 2017 eng d00aAdvances in Quantum Reinforcement Learning0 aAdvances in Quantum Reinforcement Learning c2017 a282-2873 a

In recent times, there has been much interest in quantum enhancements of machine learning, specifically in the context of data mining and analysis. Reinforcement learning, an interactive form of learning, is, in turn, vital in artificial intelligence-type applications. Also in this case, quantum mechanics was shown to be useful, in certain instances. Here, we elucidate these results, and show that quantum enhancements can be achieved in a new setting: the setting of learning models which learn how to improve themselves -- that is, those that meta-learn. While not all learning models meta-learn, all non-trivial models have the potential of being "lifted", enhanced, to meta-learning models. Our results show that also such models can be quantum-enhanced to make even better learners. In parallel, we address one of the bottlenecks of current quantum reinforcement learning approaches: the need for so-called oracularized variants of task environments. Here we elaborate on a method which realizes these variants, with minimal changes in the setting, and with no corruption of the operative specification of the environments. This result may be important in near-term experimental demonstrations of quantum reinforcement learning.

1 aDunjko, Vedran1 aTaylor, J., M.1 aBriegel, Hans, J. uhttps://arxiv.org/abs/1811.0867601983nas a2200157 4500008004100000245007700041210006900118260001500187300001100202490000800213520147800221100001601699700001801715700001901733856007301752 2017 eng d00aCooling a harmonic oscillator by optomechanical modification of its bath0 aCooling a harmonic oscillator by optomechanical modification of  c2017/05/31 a2236020 v1183 a

Optomechanical systems show tremendous promise for high sensitivity sensing of forces and modification of mechanical properties via light. For example, similar to neutral atoms and trapped ions, laser cooling of mechanical motion by radiation pressure can take single mechanical modes to their ground state. Conventional optomechanical cooling is able to introduce additional damping channel to mechanical motion, while keeping its thermal noise at the same level, and as a consequence, the effective temperature of the mechanical mode is lowered. However, the ratio of temperature to quality factor remains roughly constant, preventing dramatic advances in quantum sensing using this approach. Here we propose an approach for simultaneously reducing the thermal load on a mechanical resonator while improving its quality factor. In essence, we use the optical interaction to dynamically modify the dominant damping mechanism, providing an optomechanically-induced effect analogous to a phononic band gap. The mechanical mode of interest is assumed to be weakly coupled to its heat bath but strongly coupled to a second mechanical mode, which is cooled by radiation pressure coupling to a red detuned cavity field. We also identify a realistic optomechanical design that has the potential to realize this novel cooling scheme.

1 aXu, Xunnong1 aPurdy, Thomas1 aTaylor, J., M. uhttps://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.22360201586nas 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/1801.1012001465nas a2200157 4500008004100000245008500041210006900126260001500195300001100210490000700221520098400228100001701212700002501229700001601254856003701270 2017 eng d00aDisorder induced transitions in resonantly driven Floquet Topological Insulators0 aDisorder induced transitions in resonantly driven Floquet Topolo c2017/08/16 a0542070 v963 a

We investigate the effects of disorder in Floquet topological insulators (FTIs) occurring in semiconductor quantum wells. Such FTIs are induced by resonantly driving a transition between the valence and conduction band. We show that when disorder is added, the topological nature of such FTIs persists as long as there is a mobility gap at the resonant quasi-energy. For strong enough disorder, this gap closes and all the states become localized as the system undergoes a transition to a trivial insulator. Interestingly, the effects of disorder are not necessarily adverse: we show that in the same quantum well, disorder can also induce a transition from a trivial to a topological system, thereby establishing a Floquet Topological Anderson Insulator (FTAI). We identify the conditions on the driving field necessary for observing such a transition.

1 aTitum, Paraj1 aLindner, Netanel, H.1 aRefael, Gil uhttps://arxiv.org/abs/1702.0295615016nas a2200181 45000080041000002450084000412100069001252600015001943000011002094900007002205201446000227100002314687700002714710700001914737700001914756700002214775856003714797 2017 eng d00aDispersive optical detection of magnetic Feshbach resonances in ultracold gases0 aDispersive optical detection of magnetic Feshbach resonances in  c2017/08/18 a0227050 v963 a

Magnetically tunable Feshbach resonances in ultracold atomic systems are chiefly identified and characterized through time consuming atom loss spectroscopy. We describe an off-resonant dispersive optical probing technique to rapidly locate Feshbach resonances and demonstrate the method by locating four resonances of 87Rb, between the |F=1,mF=1 and |F=2,mF=0 states. Despite the loss features being 100 mG wide, we require only 21 experimental runs to explore a magnetic field range >18 G. The resonances consist of two known s-wave features in the vicinity of 9 G and 18 G and two previously unobserved p-wave features near 5 G and 10 G. We further utilize the dispersive approach to directly characterize the two-body loss dynamics for each Feshbach resonance.

1 aSawyer, Bianca, J.1 aHorvath, Milena, S. J.1 aTiesinga, Eite1 aDeb, Amita, B.1 aKjærgaard, Niels uhttps://arxiv.org/abs/1702.0221601082nas a2200181 4500008004100000022001400041245007000055210006900125260001500194300001400209490000700223520042300230100001800653700002100671700002100692700001600713856017100729 2017 eng d a1944-417600aDomination with decay in triangular matchstick arrangement graphs0 aDomination with decay in triangular matchstick arrangement graph c2017/05/14 a749 - 7660 v103 a

We provide results for the exponential dominating numbers and total exponential dominating numbers of a family of triangular grid graphs. We then prove inequalities for these numbers and compare them with inequalities that hold more generally for exponential dominating numbers of graphs.

1 aCochran, Jill1 aHenderson, Terry1 aOstrander, Aaron1 aTaylor, Ron uhttp://msp.org/involve/http://msp.org/involve/2017/10-5/index.xhtmlhttp://msp.org/involve/2017/10-5/p03.xhtmlhttp://msp.org/involve/2017/10-5/involve-v10-n5-p03-s.pdf01808nas a2200169 4500008004100000245009500041210006900136260001500205300000800220490000600228520129700234100001801531700001601549700001901565700001701584856003701601 2017 eng d00aDynamically induced robust phonon transport and chiral cooling in an optomechanical system0 aDynamically induced robust phonon transport and chiral cooling i c2017/06/19 a2050 v83 a

The transport of sound and heat, in the form of phonons, has a fundamental material limit: disorder-induced scattering. In electronic and optical settings, introduction of chiral transport - in which carrier propagation exhibits broken parity symmetry - provides robustness against such disorder by preventing elastic backscattering. Here we experimentally demonstrate a path for achieving robust phonon transport even in the presence of material disorder, by dynamically inducing chirality through traveling-wave optomechanical coupling. Using this approach, we demonstrate dramatic optically-induced chiral transport for clockwise and counterclockwise phonons in a symmetric resonator. This induced chirality also enhances isolation from the thermal bath and leads to gain-free reduction of the intrinsic damping of the phonons. Surprisingly, this passive mechanism is also accompanied by a chiral reduction in heat load leading to a novel optical cooling of the mechanics. This technique has the potential to improve upon the fundamental thermal limits of resonant mechanical sensor, which cannot be otherwise attained through conventional optomechanical cooling.

1 aKim, Seunghwi1 aXu, Xunnong1 aTaylor, J., M.1 aBahl, Gaurav uhttps://arxiv.org/abs/1609.0867401805nas a2200217 4500008004100000245005000041210005000091260001500141300001100156490000800167520121700175100002101392700001401413700002401427700001801451700002001469700001701489700002501506700001901531856003701550 2017 eng d00aEfimov States of Strongly Interacting Photons0 aEfimov States of Strongly Interacting Photons c2017/12/04 a2336010 v1193 a

We demonstrate the emergence of universal Efimov physics for interacting photons in cold gases of Rydberg atoms. We consider the behavior of three photons injected into the gas in their propagating frame, where a paraxial approximation allows us to consider them as massive particles. In contrast to atoms and nuclei, the photons have a large anisotropy between their longitudinal mass, arising from dispersion, and their transverse mass, arising from diffraction. Nevertheless, we show that in suitably rescaled coordinates the effective interactions become dominated by s-wave scattering near threshold and, as a result, give rise to an Efimov effect near unitarity, but with spatially anisotropic wavefunctions in the original coordinates. We show that the three-body loss of these Efimov trimers can be strongly suppressed and determine conditions under which these states are observable in current experiments. These effects can be naturally extended to probe few-body universality beyond three bodies, as well as the role of Efimov physics in the non-equilbrium, many-body regime.

1 aGullans, Michael1 aDiehl, S.1 aRittenhouse, S., T.1 aRuzic, B., P.1 aD'Incao, J., P.1 aJulienne, P.1 aGorshkov, Alexey, V.1 aTaylor, J., M. uhttps://arxiv.org/abs/1709.0195501775nas a2200133 4500008004100000245007500041210006900116520134900185100001901534700001601553700001601569700001901585856003701604 2017 eng d00aExponential improvements for quantum-accessible reinforcement learning0 aExponential improvements for quantumaccessible reinforcement lea3 a

Quantum computers can offer dramatic improvements over classical devices for data analysis tasks such as prediction and classification. However, less is known about the advantages that quantum computers may bring in the setting of reinforcement learning, where learning is achieved via interaction with a task environment. Here, we consider a special case of reinforcement learning, where the task environment allows quantum access. In addition, we impose certain "naturalness" conditions on the task environment, which rule out the kinds of oracle problems that are studied in quantum query complexity (and for which quantum speedups are well-known). Within this framework of quantum-accessible reinforcement learning environments, we demonstrate that quantum agents can achieve exponential improvements in learning efficiency, surpassing previous results that showed only quadratic improvements. A key step in the proof is to construct task environments that encode well-known oracle problems, such as Simon's problem and Recursive Fourier Sampling, while satisfying the above "naturalness" conditions for reinforcement learning. Our results suggest that quantum agents may perform well in certain game-playing scenarios, where the game has recursive structure, and the agent can learn by playing against itself

1 aDunjko, Vedran1 aLiu, Yi-Kai1 aWu, Xingyao1 aTaylor, J., M. uhttps://arxiv.org/abs/1710.1116011923nas a2200205 45000080041000002450079000412100069001202600015001893000011002044900007002155201127900222100001911501700002511520700002011545700001711565700002311582700002011605700002311625856006911648 2017 eng d00aGenuine N -partite entanglement without N -partite correlation functions0 aGenuine N partite entanglement without N partite correlation fun c2017/06/26 a0623310 v953 a

A genuinely N-partite entangled state may display vanishing N-partite correlations measured for arbitrary local observables. In such states the genuine entanglement is noticeable solely in correlations between subsets of particles. A straightforward way to obtain such states for odd N is to design an “antistate” in which all correlations between an odd number of observers are exactly opposite. Evenly mixing a state with its antistate then produces a mixed state with no N-partite correlations, with many of them genuinely multiparty entangled. Intriguingly, all known examples of “entanglement without correlations” involve an odd number of particles. Here we further develop the idea of antistates, thereby shedding light on the different properties of even and odd particle systems. We conjecture that there is no antistate to any pure even-N-party entangled state making the simple construction scheme unfeasible. However, as we prove by construction, higher-rank examples of entanglement without correlations for arbitrary even N indeed exist. These classes of states exhibit genuine entanglement and even violate an N-partite Bell inequality, clearly demonstrating the nonclassical features of these states as well as showing their applicability for quantum information processing.

1 aTran, Minh, C.1 aZuppardo, Margherita1 ade Rosier, Anna1 aKnips, Lukas1 aLaskowski, Wieslaw1 aPaterek, Tomasz1 aWeinfurter, Harald uhttps://journals.aps.org/pra/abstract/10.1103/PhysRevA.95.06233101552nas a2200181 4500008004100000245007900041210006900120260001500189300001100204490000700215520101200222100002101234700001901255700001901274700001901293700002101312856003701333 2017 eng d00aHigh-Order Multipole Radiation from Quantum Hall States in Dirac Materials0 aHighOrder Multipole Radiation from Quantum Hall States in Dirac  c2017/06/30 a2354390 v953 a

Topological states can exhibit electronic coherence on macroscopic length scales. When the coherence length exceeds the wavelength of light, one can expect new phenomena to occur in the optical response of these states. We theoretically characterize this limit for integer quantum Hall states in two-dimensional Dirac materials. We find that the radiation from the bulk is dominated by dipole emission, whose spectral properties vary with the local disorder potential. On the other hand, the radiation from the edge is characterized by large multipole moments in the far-field associated with the efficient transfer of angular momentum from the electrons into the scattered light. These results demonstrate that high-order multipole transitions are a necessary component for the optical spectroscopy and control of quantum Hall and related topological states in electronic systems.

1 aGullans, Michael1 aTaylor, J., M.1 aImamoglu, Atac1 aGhaemi, Pouyan1 aHafezi, Mohammad uhttps://arxiv.org/abs/1701.0346401674nas 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.96.23543401058nas a2200133 4500008004100000245007000041210006800111520062100179100001900800700002400819700001900843700002500862856003700887 2017 eng d00aLieb-Robinson bounds on n-partite connected correlation functions0 aLiebRobinson bounds on npartite connected correlation functions3 a

Lieb and Robinson provided bounds on how fast bipartite connected correlations can arise in systems with only short-range interactions. We generalize Lieb-Robinson bounds on bipartite connected correlators to multipartite connected correlators. The bounds imply that an n-partite connected correlator can reach unit value in constant time. Remarkably, the bounds also allow for an n-partite connected correlator to reach a value that is exponentially large with system size in constant time, a feature which stands in contrast to bipartite connected correlations. We provide explicit examples of such systems.

1 aTran, Minh, C.1 aGarrison, James, R.1 aGong, Zhe-Xuan1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1705.0435504237nas a2200157 4500008004100000245006100041210005900102260001500161490000700176520377200183100001903955700002403974700001903998700002504017856003704042 2017 eng d00aLieb-Robinson bounds on n-partite connected correlations0 aLiebRobinson bounds on npartite connected correlations c2017/11/270 v963 a

Lieb and Robinson provided bounds on how fast bipartite connected correlations can arise in systems with only short-range interactions. We generalize Lieb-Robinson bounds on bipartite connected correlators to multipartite connected correlators. The bounds imply that an n-partite connected correlator can reach unit value in constant time. Remarkably, the bounds also allow for an n-partite connected correlator to reach a value that is exponentially large with system size in constant time, a feature which stands in contrast to bipartite connected correlations. We provide explicit examples of such systems.

1 aTran, Minh, C.1 aGarrison, James, R.1 aGong, Zhe-Xuan1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1705.0435502365nas a2200181 4500008004100000245008600041210006900127260001500196520178600211100002601997700002402023700002002047700001602067700002402083700002002107700001902127856003702146 2017 eng d00aMachine Learning techniques for state recognition and auto-tuning in quantum dots0 aMachine Learning techniques for state recognition and autotuning c2017/12/133 a

Recent progress in building large-scale quantum devices for exploring quantum computing and simulation paradigms has relied upon effective tools for achieving and maintaining good experimental parameters, i.e. tuning up devices. In many cases, including in quantum-dot based architectures, the parameter space grows substantially with the number of qubits, and may become a limit to scalability. Fortunately, machine learning techniques for pattern recognition and image classification using so-called deep neural networks have shown surprising successes for computer-aided understanding of complex systems. In this work, we use deep and convolutional neural networks to characterize states and charge configurations of semiconductor quantum dot arrays when one can only measure a current-voltage characteristic of transport (here conductance) through such a device. For simplicity, we model a semiconductor nanowire connected to leads and capacitively coupled to depletion gates using the Thomas-Fermi approximation and Coulomb blockade physics. We then generate labeled training data for the neural networks, and find at least 90 % accuracy for charge and state identification for single and double dots purely from the dependence of the nanowire’s conductance upon gate voltages. Using these characterization networks, we can then optimize the parameter space to achieve a desired configuration of the array, a technique we call ‘auto-tuning’. Finally, we show how such techniques can be implemented in an experimental setting by applying our approach to an experimental data set, and outline further problems in this domain, from using charge sensing data to extensions to full one and two-dimensional arrays, that can be tackled with machine learning.

1 aKalantre, Sandesh, S.1 aZwolak, Justyna, P.1 aRagole, Stephen1 aWu, Xingyao1 aZimmerman, Neil, M.1 aStewart, M., D.1 aTaylor, J., M. uhttps://arxiv.org/abs/1712.0491401596nas a2200145 4500008004100000022001400041245007300055210006900128260001500197490000700212520114700219100002201366700001901388856004301407 2017 eng d a1099-430000aOptomechanical Analogy for Toy Cosmology with Quantized Scale Factor0 aOptomechanical Analogy for Toy Cosmology with Quantized Scale Fa c2017/09/120 v193 a

The simplest cosmology—the Friedmann–Robertson–Walker–Lemaître (FRW) model— describes a spatially homogeneous and isotropic universe where the scale factor is the only dynamical parameter. Here we consider how quantized electromagnetic fields become entangled with the scale factor in a toy version of the FRW model. A system consisting of a photon, source, and detector is described in such a universe, and we find that the detection of a redshifted photon by the detector system constrains possible scale factor superpositions. Thus, measuring the redshift of the photon is equivalent to a weak measurement of the underlying cosmology. We also consider a potential optomechanical analogy system that would enable experimental exploration of these concepts. The analogy focuses on the effects of photon redshift measurement as a quantum back-action on metric variables, where the position of a movable mirror plays the role of the scale factor. By working in the rotating frame, an effective Hubble equation can be simulated with a simple free moving mirror.

1 aSmiga, Joseph, A.1 aTaylor, J., M. uhttp://www.mdpi.com/1099-4300/19/9/48501793nas a2200121 4500008004100000245007400041210006900115260001500184520140000199100001601599700001901615856003701634 2017 eng d00aOptomechanically-induced chiral transport of phonons in one dimension0 aOptomechanicallyinduced chiral transport of phonons in one dimen c2017/01/103 a

Non-reciprocal devices, with one-way transport properties, form a key component for isolating and controlling light in photonic systems. Optomechanical systems have emerged as a potential platform for optical non-reciprocity, due to ability of a pump laser to break time and parity symmetry in the system. Here we consider how the non-reciprocal behavior of light can also impact the transport of sound in optomechanical devices. We focus on the case of a quasi one dimensional optical ring resonator with many mechanical modes coupled to light via the acousto-optic effect. The addition of disorder leads to finite diffusion for phonon transport in the material, largely due to elastic backscattering between clockwise and counter-clockwise phonons. We show that a laser pump field, along with the assumption of high quality-factor, sideband-resolved optical resonances, suppresses the effects of disorder and leads to the emergence of chiral diffusion, with direction-dependent diffusion emerging in a bandwidth similar to the phase-matching bandwidth for Brillouin scattering. A simple diagrammatic theory connects the observation of reduced mechanical linewidths directly to the associated phonon diffusion properties, and helps explain recent experimental results.

1 aXu, Xunnong1 aTaylor, J., M. uhttps://arxiv.org/abs/1701.0269917147nas 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/1705.0170201311nas a2200133 4500008004100000245005700041210005700098260001500155520091500170100001701085700001901102700001901121856003701140 2017 eng d00aQuantum simulation of ferromagnetic Heisenberg model0 aQuantum simulation of ferromagnetic Heisenberg model c2017/12/143 a

Large quantum simulators, with sufficiently many qubits to be impossible to simulate classically, become hard to experimentally validate. We propose two tests of a quantum simulator with Heisenberg interaction in a linear chain of spins. In the first, we propagate half of a singlet state through a chain of spin with a ferromagnetic interaction and subsequently recover the state with an antiferromagnetic interaction. The antiferromagnetic interaction is intrinsic to the system while the ferromagnetic one can be simulated by a sequence of time-dependent controls of the antiferromagnetic interaction and Suzuki-Trotter approximations. In the second test, we use the same technique to transfer a spin singlet state from one end of a spin chain to the other. We show that the tests are robust against parametric errors in operation of the simulator and may be applicable even without error correction.

1 aWang, Yiping1 aTran, Minh, C.1 aTaylor, J., M. uhttps://arxiv.org/abs/1712.0528202019nas a2200217 4500008004100000245006500041210006300106260001500169300001100184490000600195520137300201100001601574700002501590700002101615700002701636700002601663700001801689700001601707700002301723856005501746 2017 eng d00aSimultaneous, Full Characterization of a Single-Photon State0 aSimultaneous Full Characterization of a SinglePhoton State c2017/11/15 a0410360 v73 a

As single-photon sources become more mature and are used more often in quantum information, communications, and measurement applications, their characterization becomes more important. Singlephoton-like light is often characterized by its brightness, as well as two quantum properties: the suppression of multiphoton content and the photon indistinguishability. While it is desirable to obtain these quantities from a single measurement, currently two or more measurements are required. Here, we show that using two-photon (n ¼ 2) number-resolving detectors, one can completely characterize single-photon-like states in a single measurement, where previously two or more measurements were necessary. We simultaneously determine the brightness, the suppression of multiphoton states, the indistinguishability, and the statistical distribution of Fock states to third order for a quantum light source. We find n ≥ 3 number-resolving detectors provide no additional advantage in the single-photon characterization. The new method extracts more information per experimental trial than a conventional measurement for all input states and is particularly more efficient for statistical mixtures of photon states. Thus, using this n ¼ 2, number-resolving detector scheme will provide advantages in a variety of quantum optics measurements and systems.

1 aThomay, Tim1 aPolyakov, Sergey, V.1 aGazzano, Olivier1 aGoldschmidt, Elizabeth1 aEldredge, Zachary, D.1 aHuber, Tobias1 aLoo, Vivien1 aSolomon, Glenn, S. uhttps://link.aps.org/doi/10.1103/PhysRevX.7.04103601811nas a2200145 4500008004100000245009400041210006900135260001500204520133900219100001901558700001601577700001601593700001901609856003701628 2017 eng d00aSuper-polynomial and exponential improvements for quantum-enhanced reinforcement learning0 aSuperpolynomial and exponential improvements for quantumenhanced c2017/12/123 a

Recent work on quantum machine learning has demonstrated that quantum computers can offer dramatic improvements over classical devices for data mining, prediction and classification. However, less is known about the advantages using quantum computers may bring in the more general setting of reinforcement learning, where learning is achieved via interaction with a task environment that provides occasional rewards. Reinforcement learning can incorporate data-analysis-oriented learning settings as special cases, but also includes more complex situations where, e.g., reinforcing feedback is delayed. In a few recent works, Grover-type amplification has been utilized to construct quantum agents that achieve up-to-quadratic improvements in learning efficiency. These encouraging results have left open the key question of whether super-polynomial improvements in learning times are possible for genuine reinforcement learning problems, that is problems that go beyond the other more restricted learning paradigms. In this work, we provide a family of such genuine reinforcement learning tasks. We construct quantum-enhanced learners which learn super-polynomially, and even exponentially faster than any classical reinforcement learning model, and we discuss the potential impact our results may have on future technologies.

1 aDunjko, Vedran1 aLiu, Yi-Kai1 aWu, Xingyao1 aTaylor, J., M. uhttps://arxiv.org/abs/1710.1116001333nas a2200169 4500008004100000245008100041210006900122260001500191300001100206490000700217520083100224100002001055700001501075700001701090700001901107856003701126 2017 eng d00aThermodynamic limits for optomechanical systems with conservative potentials0 aThermodynamic limits for optomechanical systems with conservativ c2017/11/13 a1841060 v963 a

The mechanical force from light – radiation pressure – provides an intrinsic nonlinear interaction. Consequently, optomechanical systems near their steady state, such as the canonical optical spring, can display non-analytic behavior as a function of external parameters. This non-analyticity, a key feature of thermodynamic phase transitions, suggests that there could be an effective thermodynamic description of optomechanical systems. Here we explicitly define the thermodynamic limit for optomechanical systems and derive a set of sufficient constraints on the system parameters as the mechanical system grows large. As an example, we show how these constraints can be satisfied in a system with Z2 symmetry and derive a free energy, allowing us to characterize this as an equilibrium phase transition.

1 aRagole, Stephen1 aXu, Haitan1 aLawall, John1 aTaylor, J., M. uhttps://arxiv.org/abs/1707.0577101530nas 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.119.09770201580nas a2200181 4500008004100000245005200041210005200093260001500145300001100160490000700171520107600178100002301254700002101277700001901298700002001317700002401337856003701361 2017 eng d00aValley Blockade in a Silicon Double Quantum Dot0 aValley Blockade in a Silicon Double Quantum Dot c2017/11/13 a2053020 v963 a

Electrical transport in double quantum dots (DQDs) illuminates many interesting features of the dots' carrier states. Recent advances in silicon quantum information technologies have renewed interest in the valley states of electrons confined in silicon. Here we show measurements of DC transport through a mesa-etched silicon double quantum dot. Comparing bias triangles (i.e., regions of allowed current in DQDs) at positive and negative bias voltages we find a systematic asymmetry in the size of the bias triangles at the two bias polarities. Asymmetries of this nature are associated with blocking of tunneling events due to the occupation of a metastable state. Several features of our data lead us to conclude that the states involved are not simple spin states. Rather, we develop a model based on selective filling of valley states in the DQD that is consistent with all of the qualitative features of our data.

1 aPerron, Justin, K.1 aGullans, Michael1 aTaylor, J., M.1 aStewart, M., D.1 aZimmerman, Neil, M. uhttps://arxiv.org/abs/1607.0610701662nas 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.6.04102701280nas a2200205 4500008004100000245005000041210005000091260001500141300001100156490000800167520073000175100002100905700002100926700001300947700001900960700001600979700001800995700002501013856003601038 2016 eng d00aEffective Field Theory for Rydberg Polaritons0 aEffective Field Theory for Rydberg Polaritons c2016/09/09 a1136010 v1173 a

We study non-perturbative effects in N-body scattering of Rydberg polaritons using effective field theory (EFT). We develop an EFT in one dimension and show how a suitably long medium can be used to prepare shallow N-body bound states. We then derive the effective N-body interaction potential for Rydberg polaritons and the associated N-body contact force that arises in the EFT. We use the contact force to find the leading order corrections to the binding energy of the N-body bound states and determine the photon number at which the EFT description breaks down. We find good agreement throughout between the predictions of EFT and numerical simulations of the exact two and three photon wavefunction transmission.

1 aGullans, Michael1 aThompson, J., D.1 aWang, Y.1 aLiang, Q., -Y.1 aVuletic, V.1 aLukin, M., D.1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1605.0565101399nas a2200157 4500008004100000245008400041210006900125260001500194300001100209490000700220520091600227100001801143700001901161700001401180856004701194 2016 eng d00aEntangling distant resonant exchange qubits via circuit quantum electrodynamics0 aEntangling distant resonant exchange qubits via circuit quantum  c2016/11/16 a2054210 v943 a

We investigate a hybrid quantum system consisting of spatially separated resonant exchange qubits, defined in three-electron semiconductor triple quantum dots, that are coupled via a superconducting transmission line resonator. Drawing on methods from circuit quantum electrodynamics and Hartmann-Hahn double resonance techniques, we analyze three specific approaches for implementing resonator-mediated two-qubit entangling gates in both dispersive and resonant regimes of interaction. We calculate entangling gate fidelities as well as the rate of relaxation via phonons for resonant exchange qubits in silicon triple dots and show that such an implementation is particularly well-suited to achieving the strong coupling regime. Our approach combines the favorable coherence properties of encoded spin qubits in silicon with the rapid and robust long-range entanglement provided by circuit QED systems.

1 aSrinivasa, V.1 aTaylor, J., M.1 aTahan, C. uhttps://doi.org/10.1103/PhysRevB.94.20542102567nas a2200145 4500008004100000245007800041210006900119260001500188520211000203100001802313700002002331700001702351700001602368856003702384 2016 eng d00aExponential Separation of Quantum Communication and Classical Information0 aExponential Separation of Quantum Communication and Classical In c2016/11/283 a
We exhibit a Boolean function for which the quantum communication complexity is exponentially larger than the classical information complexity. An exponential separation in the other direction was already known from the work of Kerenidis et. al. [SICOMP 44, pp. 1550-1572], hence our work implies that these two complexity measures are incomparable. As classical information complexity is an upper bound on quantum information complexity, which in turn is equal to amortized quantum communication complexity, our work implies that a tight direct sum result for distributional quantum communication complexity cannot hold. The function we use to present such a separation is the Symmetric k-ary Pointer Jumping function introduced by Rao and Sinha [ECCC TR15-057], whose classical communication complexity is exponentially larger than its classical information complexity. In this paper, we show that the quantum communication complexity of this function is polynomially equivalent to its classical communication complexity. The high-level idea behind our proof is arguably the simplest so far for such an exponential separation between information and communication, driven by a sequence of round-elimination arguments, allowing us to simplify further the approach of Rao and Sinha. 
As another application of the techniques that we develop, we give a simple proof for an optimal trade-off between Alice's and Bob's communication while computing the related Greater-Than function on n bits: say Bob communicates at most b bits, then Alice must send n/exp(O(b)) bits to Bob. This holds even when allowing pre-shared entanglement. We also present a classical protocol achieving this bound.
 
 
1 aAnshu, Anurag1 aTouchette, Dave1 aYao, Penghui1 aYu, Nengkun uhttps://arxiv.org/abs/1611.0894604684nas a2200145 4500008004100000245004500041210004500086260001500131520426900146100001804415700002304433700002604456700001904482856003704501 2016 eng d00aFigures of merit for quantum transducers0 aFigures of merit for quantum transducers c2016/10/043 a

Recent technical advances have sparked renewed interest in physical systems that couple simultaneously to different parts of the electromagnetic spectrum, thus enabling transduction of signals between vastly different frequencies at the level of single photons. Such hybrid systems have demonstrated frequency conversion of classical signals and have the potential of enabling quantum state transfer, e.g., between superconducting circuits and traveling optical signals. This Letter describes a simple approach for the theoretical characterization of performance for quantum transducers. Given that, in practice, one cannot attain ideal one-to-one quantum conversion, we will explore how well the transducer performs in various scenarios ranging from classical signal detection to applications for quantum information processing. While the performance of the transducer depends on the particular application in which it enters, we show that the performance can be characterized by defining two simple parameters: the signal transfer efficiency η and the added noise N.

1 aZeuthen, Emil1 aSchliesser, Albert1 aSørensen, Anders, S.1 aTaylor, J., M. uhttps://arxiv.org/abs/1610.0109901855nas a2200157 4500008004100000245011400041210006900155260001500224300001100239490000700250520131500257100001801572700002001590700001901610856006801629 2016 eng d00aA Hubbard model for ultracold bosonic atoms interacting via zero-point-energy induced three-body interactions0 aHubbard model for ultracold bosonic atoms interacting via zeropo c2016/04/19 a0436160 v933 a

We show that for ultra-cold neutral bosonic atoms held in a three-dimensional periodic potential or optical lattice, a Hubbard model with dominant, attractive three-body interactions can be generated. In fact, we derive that the effect of pair-wise interactions can be made small or zero starting from the realization that collisions occur at the zero-point energy of an optical lattice site and the strength of the interactions is energy dependent from effective-range contributions. We determine the strength of the two- and three-body interactions for scattering from van-der-Waals potentials and near Fano-Feshbach resonances. For van-der-Waals potentials, which for example describe scattering of alkaline-earth atoms, we find that the pair-wise interaction can only be turned off for species with a small negative scattering length, leaving the 88Sr isotope a possible candidate. Interestingly, for collisional magnetic Feshbach resonances this restriction does not apply and there often exist magnetic fields where the two-body interaction is small. We illustrate this result for several known narrow resonances between alkali-metal atoms as well as chromium atoms. Finally, we compare the size of the three-body interaction with hopping rates and describe limits due to three-body recombination.

1 aPaul, Saurabh1 aJohnson, P., R.1 aTiesinga, Eite uhttp://journals.aps.org/pra/abstract/10.1103/PhysRevA.93.04361601550nas a2200145 4500008004100000245009200041210006900133260001500202300001100217490000800228520107800236100002001314700001901334856005101353 2016 eng d00aInteracting atomic interferometry for rotation sensing approaching the Heisenberg Limit0 aInteracting atomic interferometry for rotation sensing approachi c2016/11/11 a2030020 v1173 a

Atom interferometers provide exquisite measurements of the properties of non-inertial frames. While atomic interactions are typically detrimental to good sensing, efforts to harness entanglement to improve sensitivity remain tantalizing. Here we explore the role of interactions in an analogy between atomic gyroscopes and SQUIDs, motivated by recent experiments realizing ring shaped traps for ultracold atoms. We explore the one-dimensional limit of these ring systems with a moving weak barrier, such as that provided by a blue-detuned laser beam. In this limit, we employ Luttinger liquid theory and find an analogy with the superconducting phase-slip qubit, in which the topological charge associated with persistent currents can be put into superposition. In particular, we find that strongly-interacting atoms in such a system could be used for precision rotation sensing. We compare the performance of this new sensor to an equivalent non-interacting atom interferometer, and find improvements in sensitivity and bandwidth beyond the atomic shot-noise limit.

1 aRagole, Stephen1 aTaylor, J., M. uhttps://doi.org/10.1103/PhysRevLett.117.20300201666nas a2200145 4500008004100000245006300041210006300104260001500167300001100182490000700193520123200200100002201432700001901454856004701473 2016 eng d00aLandauer formulation of photon transport in driven systems0 aLandauer formulation of photon transport in driven systems c2016/10/20 a1554370 v943 a

Understanding the behavior of light in non-equilibrium scenarios underpins much of quantum optics and optical physics. While lasers provide a severe example of a non-equilibrium problem, recent interests in the near-equilibrium physics of photon `gases', such as in Bose condensation of light or in attempts to make photonic quantum simulators, suggest one reexamine some near-equilibrium cases. Here we consider how a sinusoidal parametric coupling between two semi-infinite photonic transmission lines leads to the creation and flow of photons between the two lines. Our approach provides a photonic analogue to the Landauer transport formula, and using non-equilbrium Green's functions, we can extend it to the case of an interacting region between two photonic `leads' where the sinusoid frequency plays the role of a voltage bias. Crucially, we identify both the mathematical framework and the physical regime in which photonic transport is directly analogous to electronic transport, and regimes in which other new behavior such as two-mode squeezing can emerge.

1 aWang, Chiao-Hsuan1 aTaylor, J., M. uhttps://doi.org/10.1103/PhysRevB.94.15543709134nas a2200205 4500008004100000245007700041210006900118260001500187300001000202490000600212520852300218100001708741700002208758700001908780700002308799700001808822700001908840700002208859856004708881 2016 eng d00aMultiple scattering dynamics of fermions at an isolated p-wave resonance0 aMultiple scattering dynamics of fermions at an isolated pwave re c2016/07/11 a120690 v73 a

The wavefunction for indistinguishable fermions is anti-symmetric under particle exchange, which directly leads to the Pauli exclusion principle, and hence underlies the structure of atoms and the properties of almost all materials. In the dynamics of collisions between two indistinguishable fermions this requirement strictly prohibits scattering into 90 degree angles. Here we experimentally investigate the collisions of ultracold clouds fermionic 40K atoms by directly measuring scattering distributions. With increasing collision energy we identify the Wigner threshold for p-wave scattering with its tell-tale dumb-bell shape and no 90 yield. Above this threshold effects of multiple scattering become manifest as deviations from the underlying binary p-wave shape, adding particles either isotropically or axially. A shape resonance for 40K facilitates the separate observation of these two processes. The isotropically enhanced multiple scattering mode is a generic p-wave threshold phenomenon, while the axially enhanced mode should occur in any colliding particle system with an elastic scattering resonance.

1 aThomas, Ryan1 aRoberts, Kris, O.1 aTiesinga, Eite1 aWade, Andrew, C.J.1 aBlakie, Blair1 aDeb, Amita, B.1 aKjærgaard, Niels uhttp://www.nature.com/articles/ncomms1206901525nas a2200145 4500008004100000245007500041210006900116260001500185520106700200100001801267700002001285700001901305700001901324856003601343 2016 eng d00aObservation of Optomechanical Quantum Correlations at Room Temperature0 aObservation of Optomechanical Quantum Correlations at Room Tempe c2016/05/183 a

By shining laser light through a nanomechanical beam, we measure the beam's thermally driven vibrations and perturb its motion with optical forces at a level dictated by the Heisenberg measurement-disturbance uncertainty relation. Such quantum backaction is typically difficult to observe at room temperature where the motion driven by optical quantum intensity fluctuations is many orders of magnitude smaller than the thermal motion. We demonstrate a cross-correlation technique to distinguish optically driven motion from thermally driven motion, observing this quantum backaction signature up to room temperature. While it is often difficult to absolutely calibrate optical detection, we use the scale of the quantum correlations, which is determined by fundamental constants, to gauge the size of thermal motion, demonstrating a path towards absolute thermometry with quantum mechanically calibrated ticks.

1 aPurdy, T., P.1 aGrutter, K., E.1 aSrinivasan, K.1 aTaylor, J., M. uhttp://arxiv.org/abs/1605.0566401486nas a2200181 4500008004100000245004800041210004800089260001500137300001100152490000700163520100000170100001801170700002101188700002301209700001901232700001701251856003601268 2016 eng d00aPhotoassociation of spin polarized Chromium0 aPhotoassociation of spin polarized Chromium c2016/02/29 a0214060 v933 aWe report the homonuclear photoassociation (PA) of ultracold 52Cr atoms in an optical dipole trap. This constitutes the first measurement of PA in an element with total electron spin S~>1. Although Cr, with its 7S3 ground and 7P4,3,2 excited states, is expected to have a complicated PA spectrum we show that a spin polarized cloud exhibits a remarkably simple PA spectrum when circularly polarized light is applied. Over a scan range of 20 GHz below the 7P3 asymptote we observe two distinct vibrational series each following a LeRoy-Bernstein law for a C3/R3 potential with excellent agreement. We determine the C3 coefficients of the Hund's case c) relativistic adiabatic potentials to be -1.83±0.02 a.u. and -1.46±0.01a.u.. Theoretical non-rotating Movre-Pichler calculations enable a first assignment of the series to Ω=6u and 5g potential energy curves. In a different set of experiments we disturb the selection rules by a transverse magnetic field which leads to additional PA series.1 aRührig, Jahn1 aBäuerle, Tobias1 aJulienne, Paul, S.1 aTiesinga, Eite1 aPfau, Tilman uhttp://arxiv.org/abs/1512.0437800982nas a2200145 4500008004100000245004300041210004100084260001500125300001100140490000700151520059900158100002200757700001900779856003800798 2016 eng d00aA Quantum Model for an Entropic Spring0 aQuantum Model for an Entropic Spring c2016/06/01 a2141020 v933 a

Motivated by understanding the emergence of thermodynamic restoring forces and oscillations, we develop a quantum-mechanical model of a bath of spins coupled to the elasticity of a material. We show our model reproduces the behavior of a variety of entropic springs while enabling investigation of non-equilibrium resonator states in the quantum domain. We find our model emerges naturally in disordered elastic media such as glasses, and is an additional, expected effect in systems with anomalous specific heat and 1/f noise at low temperatures due to two-level systems that fluctuate.

1 aWang, Chiao-Hsuan1 aTaylor, J., M. uhttp://arxiv.org/abs/1507.08658v101010nas a2200145 4500008004100000245007200041210006800113260001500181490000700196520056900203100001800772700001900790700001900809856003600828 2016 eng d00aA Quantum Version of Schöning's Algorithm Applied to Quantum 2-SAT0 aQuantum Version of Schönings Algorithm Applied to Quantum 2SAT c2016/03/220 v163 a

We study a quantum algorithm that consists of a simple quantum Markov process, and we analyze its behavior on restricted versions of Quantum 2-SAT. We prove that the algorithm solves this decision problem with high probability for n qubits, L clauses, and promise gap c in time O(n^2 L^2 c^{-2}). If the Hamiltonian is additionally polynomially gapped, our algorithm efficiently produces a state that has high overlap with the satisfying subspace. The Markov process we study is a quantum analogue of Sch\"oning's probabilistic algorithm for k-SAT.

1 aFarhi, Edward1 aKimmel, Shelby1 aTemme, Kristan uhttp://arxiv.org/abs/1603.0698501578nas a2200157 4500008004100000245003800041210003700079260001500116300001100131490000800142520115100150100001901301700001901320700002201339856005901361 2016 eng d00aQuantum-Enhanced Machine Learning0 aQuantumEnhanced Machine Learning c2016/09/20 a1305010 v1173 a

The emerging field of quantum machine learning has the potential to substantially aid in the problems and scope of artificial intelligence. This is only enhanced by recent successes in the field of classical machine learning. In this work we propose an approach for the systematic treatment of machine learning, from the perspective of quantum information. Our approach is general and covers all three main branches of machine learning: supervised, unsupervised, and reinforcement learning. While quantum improvements in supervised and unsupervised learning have been reported, reinforcement learning has received much less attention. Within our approach, we tackle the problem of quantum enhancements in reinforcement learning as well, and propose a systematic scheme for providing improvements. As an example, we show that quadratic improvements in learning efficiency, and exponential improvements in performance over limited time periods, can be obtained for a broad class of learning problems.

1 aDunjko, Vedran1 aTaylor, J., M.1 aBriegel, Hans, J. uhttp://link.aps.org/doi/10.1103/PhysRevLett.117.13050101938nas a2200145 4500008004100000245004200041210003900083260001500122520154800137100001601685700001801701700001701719700001901736856003701755 2016 eng d00aA quasi-mode theory of chiral phonons0 aquasimode theory of chiral phonons c2016/12/293 a

The coherence properties of mechanical resonators are often limited by multiple unavoidable forms of loss -- including phonon-phonon and phonon-defect scattering -- which result in the scattering of sound into other resonant modes and into the phonon bath. Dynamic suppression of this scattering loss can lift constraints on device structure and can improve tolerance to defects in the material, even after fabrication. Inspired by recent experiments, here we introduce a model of phonon losses resulting from disorder in a whispering gallery mode resonator with acousto-optical coupling between optical and mechanical modes. We show that a typical elastic scattering mechanism of high quality factor (Q) mechanical modes flips the direction of phonon propagation via high-angle scattering, leading to damping into modes with the opposite parity. When the optical mode overlaps co-propagating high-Q and bulk mechanical modes, the addition of laser cooling via sideband-resolved damping of the mechanical mode of a chosen parity also damps and modifies the response of the bulk modes of the same parity. This, in turn, simultaneously improves the quality factor and reduces the thermal load of the counter-propagating high-Q modes, leading to the dynamical creation of a cold phononic shield. We compare our theoretical results to the recent experiments of Kim et al., and find quantitative agreement with our theory.

1 aXu, Xunnong1 aKim, Seunghwi1 aBahl, Gaurav1 aTaylor, J., M. uhttps://arxiv.org/abs/1612.0924001512nas a2200157 4500008004100000245008700041210006900128260001500197300001100212490000700223520099300230100002501223700001401248700001901262856007301281 2016 eng d00aSerialized Quantum Error Correction Protocol for High-Bandwidth Quantum Repeaters0 aSerialized Quantum Error Correction Protocol for HighBandwidth Q c2016/09/02 a0930080 v183 a

Advances in single photon creation, transmission, and detection suggest that sending quantum information over optical fibers may have losses low enough to be correctable using a quantum error correcting code. Such error-corrected communication is equivalent to a novel quantum repeater scheme, but crucial questions regarding implementation and system requirements remain open. Here we show that long range entangled bit generation with rates approaching $10^8$ ebits/s may be possible using a completely serialized protocol, in which photons are generated, entangled, and error corrected via sequential, one-way interactions with a minimal number of matter qubits. Provided loss and error rates of the required elements are below the threshold for quantum error correction, this scheme demonstrates improved performance over transmission of single photons. We find improvement in ebit rates at large distances using this serial protocol and various quantum error correcting codes.

1 aGlaudell, Andrew, N.1 aWaks, Edo1 aTaylor, J., M. uhttp://iopscience.iop.org/article/10.1088/1367-2630/18/9/093008/meta01372nas a2200181 4500008004100000245007800041210006900119260001500188300001100203490000800214520084100222100002101063700001601084700001701100700001801117700001901135856003601154 2016 eng d00aSisyphus Thermalization of Photons in a Cavity-Coupled Double Quantum Dot0 aSisyphus Thermalization of Photons in a CavityCoupled Double Qua c2016/07/25 a0568010 v1173 a

A strongly driven quantum system, coupled to a thermalizing bath, generically evolves into a highly non-thermal state as the external drive competes with the equilibrating force of the bath. We demonstrate a notable exception to this picture for a microwave resonator interacting with a periodically driven double quantum dot (DQD). In the limit of strong driving and long times, we show that the resonator field can be driven into a thermal state with a chemical potential given by a harmonic of the drive frequency. Such tunable chemical potentials are achievable with current devices and would have broad utility for quantum simulation in circuit quantum electrodynamics. As an example, we show how several DQDs embedded in an array of microwave resonators can induce a phase transition to a Bose-Einstein condensate of light.

1 aGullans, Michael1 aStehlik, J.1 aLiu, Y., -Y.1 aPetta, J., R.1 aTaylor, J., M. uhttp://arxiv.org/abs/1512.0124809346nas a2200181 4500008004100000245005500041210005400096260001500150520881500165100001908980700001608999700002309015700002409038700002009062700002009082700002509102856003709127 2016 eng d00aSteady-state superradiance with Rydberg polaritons0 aSteadystate superradiance with Rydberg polaritons c2016/11/023 a

A steady-state superradiant laser can be used to generate ultranarrow-linewidth light, and thus has important applications in the fields of quantum information and precision metrology. However, the light produced by such a laser is still essentially classical. Here, we show that the introduction of a Rydberg medium into a cavity containing atoms with a narrow optical transition can lead to the steady-state superradiant emission of ultranarrow-linewidth nonclassical light. The cavity nonlinearity induced by the Rydberg medium strongly modifies the superradiance threshold, and leads to a Mollow triplet in the cavity output spectrumthis behavior can be understood as an unusual analogue of resonance fluorescence. The cavity output spectrum has an extremely sharp central peak, with a linewidth that can be far narrower than that of a classical superradiant laser. This unprecedented spectral sharpness, together with the nonclassical nature of the light, could lead to new applications in which spectrally pure quantum light is desired.

1 aGong, Zhe-Xuan1 aXu, Minghui1 aFoss-Feig, Michael1 aThompson, James, K.1 aRey, Ana, Maria1 aHolland, Murray1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1611.0079701465nas a2200205 4500008004100000245006900041210006800110260001500178300001100193490000700204520085500211100002201066700001401088700001901102700002001121700002101141700001701162700002501179856005501204 2016 eng d00aSubwavelength-width optical tunnel junctions for ultracold atoms0 aSubwavelengthwidth optical tunnel junctions for ultracold atoms c2016/12/27 a0634220 v943 a

We propose a method for creating far-field optical barrier potentials for ultracold atoms with widths that are narrower than the diffraction limit and can approach tens of nanometers. The reduced widths stem from the nonlinear atomic response to control fields that create spatially varying dark resonances. The subwavelength barrier is the result of the geometric scalar potential experienced by an atom prepared in such a spatially varying dark state. The performance of this technique, as well as its applications to the study of many-body physics and to the implementation of quantum-information protocols with ultracold atoms, are discussed, with a focus on the implementation of tunnel junctions.

1 aJendrzejewski, F.1 aEckel, S.1 aTiecke, T., G.1 aJuzeliūnas, G.1 aCampbell, G., K.1 aJiang, Liang1 aGorshkov, Alexey, V. uhttp://link.aps.org/doi/10.1103/PhysRevA.94.06342201747nas 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/1602.0097913859nas a2200145 45000080041000002450084000412100069001252600015001943000011002094900007002205201338100227100001813608700001913626856006813645 2016 eng d00aWannier functions using a discrete variable representation for optical lattices0 aWannier functions using a discrete variable representation for o c2016/09/07 a0336060 v943 a

We propose a numerical method using the discrete variable representation (DVR) for constructing real-valued Wannier functions localized in a unit cell for both symmetric and asymmetric periodic potentials. We apply these results to finding Wannier functions for ultracold atoms trapped in laser-generated optical lattices. Following S. Kivelson [Phys. Rev. B 26, 4269 (1982)], for a symmetric lattice with inversion symmetry, we construct Wannier functions as eigenstates of the position operators xˆ, yˆ, and zˆ restricted to single-particle Bloch functions belonging to one or more bands. To ensure that the Wannier functions are real-valued, we numerically obtain the band structure and real-valued eigenstates using a uniform Fourier grid DVR. We then show, by a comparison of tunneling energies, that the Wannier functions are accurate for both inversion-symmetric and asymmetric potentials to better than 10 significant digits when using double-precision arithmetic. The calculations are performed for an optical lattice with double-wells per unit cell with tunable asymmetry along the x axis and a single sinusoidal potential along the perpendicular directions. Localized functions at the two potential minima within each unit cell are similarly constructed, but using a superposition of single-particle solutions from the two lowest bands. We finally use these localized basis functions to determine the two-body interaction energies in the Bose-Hubbard model and show the dependence of these energies on lattice asymmetry.

1 aPaul, Saurabh1 aTiesinga, Eite uhttp://journals.aps.org/pra/abstract/10.1103/PhysRevA.94.03360601241nas 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/1404.3214v202139nas a2200145 4500008004100000245008500041210006900126260001500195300001100210490000700221520169100228100001801919700001901937856003701956 2015 eng d00aCapacitively coupled singlet-triplet qubits in the double charge resonant regime0 aCapacitively coupled singlettriplet qubits in the double charge  c2015/12/01 a2353010 v923 aWe investigate a method for entangling two singlet-triplet qubits in adjacent double quantum dots via capacitive interactions. In contrast to prior work, here we focus on a regime with strong interactions between the qubits. The interplay of the interaction energy and simultaneous large detunings for both double dots gives rise to the double charge resonant regime, in which the unpolarized (1111) and fully polarized (0202) four-electron states in the absence of interqubit tunneling are near degeneracy, while being energetically well-separated from the partially polarized (0211 and 1102) states. A controlled-phase gate may be realized by combining time evolution in this regime in the presence of intraqubit tunneling and the interqubit Coulomb interaction with refocusing {\pi} pulses that swap the singly occupied singlet and triplet states of the two qubits via, e.g., magnetic gradients. We calculate the fidelity of this entangling gate, incorporating models for two types of noise - classical, Gaussian-distributed charge fluctuations in the single-qubit detunings and charge relaxation within the low-energy subspace via electron-phonon interaction - and identify parameter regimes that optimize the fidelity. The rates of phonon-induced decay for pairs of GaAs or Si double quantum dots vary with the sizes of the dipolar and quadrupolar contributions and are several orders of magnitude smaller for Si, leading to high theoretical gate fidelities for coupled singlet-triplet qubits in Si dots. We also consider the dependence of the capacitive coupling on the relative orientation of the double dots and find that a linear geometry provides the fastest potential gate. 1 aSrinivasa, V.1 aTaylor, J., M. uhttp://arxiv.org/abs/1408.4740v201437nas a2200157 4500008004100000245003500041210003300076260001500109300001100124490000700135520104900142100001501191700001701206700001901223856003701242 2015 eng d00aA chemical potential for light0 achemical potential for light c2014/05/22 a1743050 v923 aPhotons are not conserved in interactions with other matter. Consequently, when understanding the equation of state and thermodynamics of photons, while we have a concept of temperature for energy conservation, there is no equivalent chemical potential for particle number conservation. However, the notion of a chemical potential is crucial in understanding a wide variety of single- and many-body effects, from transport in conductors and semi-conductors to phase transitions in electronic and atomic systems. Here we show how a direct modification of the system-bath coupling via parametric oscillation creates an effective chemical potential for photons even in the thermodynamic limit. Specific implementations, using circuit-QED or optomechanics, are feasible using current technologies, and we show a detailed example demonstrating the emergence of Mott Insulator-superfluid transition in a lattice of nonlinear oscillators. Our approach paves the way for quantum simulation, quantum sources and even electron-like circuits with light. 1 aHafezi, M.1 aAdhikari, P.1 aTaylor, J., M. uhttp://arxiv.org/abs/1405.5821v201280nas a2200133 4500008004100000245005800041210005800099260001500157520087600172100001901048700001901067700002201086856003801108 2015 eng d00aFramework for learning agents in quantum environments0 aFramework for learning agents in quantum environments c2015/07/303 aIn this paper we provide a broad framework for describing learning agents in general quantum environments. We analyze the types of classically specified environments which allow for quantum enhancements in learning, by contrasting environments to quantum oracles. We show that whether or not quantum improvements are at all possible depends on the internal structure of the quantum environment. If the environments are constructed and the internal structure is appropriately chosen, or if the agent has limited capacities to influence the internal states of the environment, we show that improvements in learning times are possible in a broad range of scenarios. Such scenarios we call luck-favoring settings. The case of constructed environments is particularly relevant for the class of model-based learning agents, where our results imply a near-generic improvement. 1 aDunjko, Vedran1 aTaylor, J., M.1 aBriegel, Hans, J. uhttp://arxiv.org/abs/1507.08482v101274nas a2200181 4500008004100000245010400041210006900145260001500214300001200229490000800241520071300249100002100962700001500983700002100998700001901019700001701038856003701055 2015 eng d00aFrom membrane-in-the-middle to mirror-in-the-middle with a high-reflectivity sub-wavelength grating0 aFrom membraneinthemiddle to mirrorinthemiddle with a highreflect c2015/01/02 a81 - 880 v5273 aWe demonstrate a "membrane in the middle" optomechanical system using a silicon nitride membrane patterned as a subwavelength grating. The grating has a reflectivity of over 99.8%, effectively creating two sub-cavities, with free spectral ranges of 6 GHz, optically coupled via photon tunneling. Measurements of the transmission and reflection spectra show an avoided crossing where the two sub-cavities simultaneously come into resonance, with a frequency splitting of 54 MHz. We derive expressions for the lineshapes of the symmetric and antisymmetric modes at the avoided crossing, and infer the grating reflection, transmission, absorption, and scattering through comparison with the experimental data. 1 aStambaugh, Corey1 aXu, Haitan1 aKemiktarak, Utku1 aTaylor, J., M.1 aLawall, John uhttp://arxiv.org/abs/1407.1709v101515nas a2200181 4500008004100000245007100041210006900112260001500181300001100196490000700207520099200214100001701206700001601223700002101239700001901260700001801279856003601297 2015 eng d00aInjection Locking of a Semiconductor Double Quantum Dot Micromaser0 aInjection Locking of a Semiconductor Double Quantum Dot Micromas c2015/11/02 a0538020 v923 a Emission linewidth is an important figure of merit for masers and lasers. We recently demonstrated a semiconductor double quantum dot (DQD) micromaser where photons are generated through single electron tunneling events. Charge noise directly couples to the DQD energy levels, resulting in a maser linewidth that is more than 100 times larger than the Schawlow-Townes prediction. Here we demonstrate a linewidth narrowing of more than a factor 10 by locking the DQD emission to a coherent tone that is injected to the input port of the cavity. We measure the injection locking range as a function of cavity input power and show that it is in agreement with the Adler equation. The position and amplitude of distortion sidebands that appear outside of the injection locking range are quantitatively examined. Our results show that this unconventional maser, which is impacted by strong charge noise and electron-phonon coupling, is well described by standard laser models. 1 aLiu, Y., -Y.1 aStehlik, J.1 aGullans, Michael1 aTaylor, J., M.1 aPetta, J., R. uhttp://arxiv.org/abs/1508.0414701804nas a2200145 4500008004100000245007600041210006900117260001500186300001100201490000700212520133400219100001801553700001901571856006801590 2015 eng d00aLarge effective three-body interaction in a double-well optical lattice0 aLarge effective threebody interaction in a doublewell optical la c2015/08/03 a0236020 v923 a We study ultracold atoms in an optical lattice with two local minima per unit cell and show that the low energy states of a multi-band Bose-Hubbard (BH) Hamiltonian with only pair-wise interactions is equivalent to an effective single-band Hamiltonian with strong three-body interactions. We focus on a double-well optical lattice with a symmetric double well along the $x$ axis and single well structure along the perpendicular directions. Tunneling and two-body interaction energies are obtained from an exact band-structure calculation and numerically-constructed Wannier functions in order to construct a BH Hamiltonian spanning the lowest two bands. Our effective Hamiltonian is constructed from the ground state of the $N$-atom Hamiltonian for each unit cell obtained within the subspace spanned by the Wannier functions of two lowest bands. The model includes hopping between ground states of neighboring unit cells. We show that such an effective Hamiltonian has strong three-body interactions that can be easily tuned by changing the lattice parameters. Finally, relying on numerical mean-field simulations, we show that the effective Hamiltonian is an excellent approximation of the two-band BH Hamiltonian over a wide range of lattice parameters, both in the superfluid and Mott insulator regions. 1 aPaul, Saurabh1 aTiesinga, Eite uhttp://journals.aps.org/pra/abstract/10.1103/PhysRevA.92.02360201704nas a2200169 4500008004100000245006100041210006100102260001500163520120900178100001501387700002101402700001701423700002001440700001701460700001901477856003801496 2015 eng d00aObservation of optomechanical buckling phase transitions0 aObservation of optomechanical buckling phase transitions c2015/10/163 a

Correlated phases of matter provide long-term stability for systems as diverse as solids, magnets, and potential exotic quantum materials. Mechanical systems, such as relays and buckling transition spring switches can yield similar stability by exploiting non-equilibrium phase transitions. Curiously, in the optical domain, observations of such phase transitions remain elusive. However, efforts to integrate optical and mechanical systems -- optomechanics -- suggest that a hybrid approach combining the quantum control of optical systems with the engineerability of mechanical systems may provide a new avenue for such explorations. Here we report the first observation of the buckling of an optomechanical system, in which transitions between stable mechanical states corresponding to both first- and second-order phase transitions are driven by varying laser power and detuning. Our results enable new applications in photonics and, given rapid progress in pushing optomechanical systems into the quantum regime, the potential for explorations of quantum phase transitions.

1 aXu, Haitan1 aKemiktarak, Utku1 aFan, Jingyun1 aRagole, Stephen1 aLawall, John1 aTaylor, J., M. uhttp://arxiv.org/abs/1510.04971v101701nas a2200145 4500008004100000245005200041210005200093260001500145300001100160490000700171520130100178100002101479700001901500856003601519 2015 eng d00aOptical Control of Donor Spin Qubits in Silicon0 aOptical Control of Donor Spin Qubits in Silicon c2015/11/11 a1954110 v923 aWe show how to achieve optical, spin-selective transitions from the ground state to excited orbital states of group-V donors (P, As, Sb, Bi) in silicon. We consider two approaches based on either resonant, far-infrared (IR) transitions of the neutral donor or resonant, near-IR excitonic transitions. For far-IR light, we calculate the dipole matrix elements between the valley-orbit and spin-orbit split states for all the goup-V donors using effective mass theory. We then calculate the maximum rate and amount of electron-nuclear spin-polarization achievable through optical pumping with circularly polarized light. We find this approach is most promising for Bi donors due to their large spin-orbit and valley-orbit interactions. Using near-IR light, spin-selective excitation is possible for all the donors by driving a two-photon $\Lambda$-transition from the ground state to higher orbitals with even parity. We show that externally applied electric fields or strain allow similar, spin-selective $\Lambda$-transition to odd-parity excited states. We anticipate these results will be useful for future spectroscopic investigations of donors, quantum control and state preparation of donor spin qubits, and for developing a coherent interface between donor spin qubits and single photons. 1 aGullans, Michael1 aTaylor, J., M. uhttp://arxiv.org/abs/1507.0792901328nas 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-10-40-1-10501003nas a2200181 4500008004100000245006900041210006800110260001500178300001100193490000800204520048000212100002100692700001700713700001600730700001800746700001900764856003800783 2015 eng d00aPhonon-Assisted Gain in a Semiconductor Double Quantum Dot Maser0 aPhononAssisted Gain in a Semiconductor Double Quantum Dot Maser c2015/05/13 a1968020 v1143 aWe develop a microscopic model for the recently demonstrated double quantum dot (DQD) maser. In characterizing the gain of this device we find that, in addition to the direct stimulated emission of photons, there is a large contribution from the simultaneous emission of a photon and a phonon, i.e., the phonon sideband. We show that this phonon-assisted gain typically dominates the overall gain which leads to masing. Recent experimental data are well fit with our model. 1 aGullans, Michael1 aLiu, Y., -Y.1 aStehlik, J.1 aPetta, J., R.1 aTaylor, J., M. uhttp://arxiv.org/abs/1501.03499v301482nas a2200157 4500008004100000245006300041210006300104260001500167300001100182490000700193520103100200100001601231700002101247700001901268856003701287 2015 eng d00aQuantum Nonlinear Optics Near Optomechanical Instabilities0 aQuantum Nonlinear Optics Near Optomechanical Instabilities c2015/01/09 a0138180 v913 a Optomechanical systems provide a unique platform for observing quantum behavior of macroscopic objects. However, efforts towards realizing nonlinear behavior at the single photon level have been inhibited by the small size of the radiation pressure interaction. Here we show that it is not necessary to reach the single-photon strong-coupling regime in order to realize significant optomechanical nonlinearities. Instead, nonlinearities at the few quanta level can be achieved, even with weak-coupling, in a two-mode optomechanical system driven near instability. In this limit, we establish a new figure of merit for realizing strong nonlinearity which scales with the single-photon optomechanical coupling and the sideband resolution of the mechanical mode with respect to the cavity linewidth. We find that current devices based on optomechanical crystals, thought to be in the weak-coupling regime, can still achieve strong quantum nonlinearity; enabling deterministic interactions between single photons. 1 aXu, Xunnong1 aGullans, Michael1 aTaylor, J., M. uhttp://arxiv.org/abs/1404.3726v201945nas 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/1506.09149v201150nas a2200193 4500008004100000245004800041210004800089260001500137300001400152490000800166520063700174100001700811700001600828700001600844700002100860700001900881700001800900856003800918 2015 eng d00aSemiconductor double quantum dot micromaser0 aSemiconductor double quantum dot micromaser c2015/01/15 a285 - 2870 v3473 a The coherent generation of light, from masers to lasers, relies upon the specific structure of the individual emitters that lead to gain. Devices operating as lasers in the few-emitter limit provide opportunities for understanding quantum coherent phenomena, from THz sources to quantum communication. Here we demonstrate a maser that is driven by single electron tunneling events. Semiconductor double quantum dots (DQDs) serve as a gain medium and are placed inside of a high quality factor microwave cavity. We verify maser action by comparing the statistics of the emitted microwave field above and below the maser threshold. 1 aLiu, Y., -Y.1 aStehlik, J.1 aEichler, C.1 aGullans, Michael1 aTaylor, J., M.1 aPetta, J., R. uhttp://arxiv.org/abs/1507.06359v101158nas a2200157 4500008004100000245007300041210006900114260001500183300001100198490000800209520069800217100001800915700001100933700001900944856003700963 2015 eng d00aTunable Spin Qubit Coupling Mediated by a Multi-Electron Quantum Dot0 aTunable Spin Qubit Coupling Mediated by a MultiElectron Quantum  c2015/06/04 a2268030 v1143 aWe present an approach for entangling electron spin qubits localized on spatially separated impurity atoms or quantum dots via a multi-electron, two-level quantum dot. The effective exchange interaction mediated by the dot can be understood as the simplest manifestation of Ruderman-Kittel-Kasuya-Yosida exchange, and can be manipulated through gate voltage control of level splittings and tunneling amplitudes within the system. This provides both a high degree of tuneability and a means for realizing high-fidelity two-qubit gates between spatially separated spins, yielding an experimentally accessible method of coupling donor electron spins in silicon via a hybrid impurity-dot system. 1 aSrinivasa, V.1 aXu, H.1 aTaylor, J., M. uhttp://arxiv.org/abs/1312.1711v302343nas a2200169 4500008004100000245009200041210006900133260001500202300001400217490000800231520180600239100002602045700002002071700002402091700002102115856003702136 2014 eng d00aAdaptive change of basis in entropy-based moment closures for linear kinetic equations0 aAdaptive change of basis in entropybased moment closures for lin c2014/02/01 a489 - 5080 v2583 a Entropy-based (M_N) moment closures for kinetic equations are defined by a constrained optimization problem that must be solved at every point in a space-time mesh, making it important to solve these optimization problems accurately and efficiently. We present a complete and practical numerical algorithm for solving the dual problem in one-dimensional, slab geometries. The closure is only well-defined on the set of moments that are realizable from a positive underlying distribution, and as the boundary of the realizable set is approached, the dual problem becomes increasingly difficult to solve due to ill-conditioning of the Hessian matrix. To improve the condition number of the Hessian, we advocate the use of a change of polynomial basis, defined using a Cholesky factorization of the Hessian, that permits solution of problems nearer to the boundary of the realizable set. We also advocate a fixed quadrature scheme, rather than adaptive quadrature, since the latter introduces unnecessary expense and changes the computationally realizable set as the quadrature changes. For very ill-conditioned problems, we use regularization to make the optimization algorithm robust. We design a manufactured solution and demonstrate that the adaptive-basis optimization algorithm reduces the need for regularization. This is important since we also show that regularization slows, and even stalls, convergence of the numerical simulation when refining the space-time mesh. We also simulate two well-known benchmark problems. There we find that our adaptive-basis, fixed-quadrature algorithm uses less regularization than alternatives, although differences in the resulting numerical simulations are more sensitive to the regularization strategy than to the choice of basis. 1 aAlldredge, Graham, W.1 aHauck, Cory, D.1 aO'Leary, Dianne, P.1 aTits, André, L. uhttp://arxiv.org/abs/1306.2881v101005nas 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/1401.0946v102620nas a2200253 4500008004100000245007300041210006900114260001300183300001200196490000800208520192500216100001402141700001702155700001502172700002302187700001602210700001402226700001902240700001802259700001402277700001902291700001902310856003702329 2014 eng d00aOptical detection of radio waves through a nanomechanical transducer0 aOptical detection of radio waves through a nanomechanical transd c2014/3/5 a81 - 850 v5073 aLow-loss transmission and sensitive recovery of weak radio-frequency (rf) and microwave signals is an ubiquitous technological challenge, crucial in fields as diverse as radio astronomy, medical imaging, navigation and communication, including those of quantum states. Efficient upconversion of rf-signals to an optical carrier would allow transmitting them via optical fibers dramatically reducing losses, and give access to the mature toolbox of quantum optical techniques, routinely enabling quantum-limited signal detection. Research in the field of cavity optomechanics has shown that nanomechanical oscillators can couple very strongly to either microwave or optical fields. An oscillator accommodating both functionalities would bear great promise as the intermediate platform in a radio-to-optical transduction cascade. Here, we demonstrate such an opto-electro-mechanical transducer utilizing a high-Q nanomembrane. A moderate voltage bias (<10V) is sufficient to induce strong coupling between the voltage fluctuations in a rf resonance circuit and the membrane's displacement, which is simultaneously coupled to light reflected off its metallized surface. The circuit acts as an antenna; the voltage signals it induces are detected as an optical phase shift with quantum-limited sensitivity. The half-wave voltage is in the microvolt range, orders of magnitude below that of standard optical modulators. The noise added by the membrane is suppressed by the electro-mechanical cooperativity C~6800 and has a temperature of 40mK, far below 300K where the entire device is operated. This corresponds to a sensitivity limit as low as 5 pV/Hz^1/2, or -210dBm/Hz in a narrow band around 1 MHz. Our work introduces an entirely new approach to all-optical, ultralow-noise detection of classical electronic signals, and sets the stage for coherent upconversion of low-frequency quantum signals to the optical domain. 1 aBagci, T.1 aSimonsen, A.1 aSchmid, S.1 aVillanueva, L., G.1 aZeuthen, E.1 aAppel, J.1 aTaylor, J., M.1 aSørensen, A.1 aUsami, K.1 aSchliesser, A.1 aPolzik, E., S. uhttp://arxiv.org/abs/1307.3467v201850nas 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/1406.0937v101000nas a2200121 4500008004100000245007700041210006900118260001500187520059900202100002100801700001900822856003700841 2014 eng d00aA Quantum Network of Silicon Qubits using Mid-Infrared Graphene Plasmons0 aQuantum Network of Silicon Qubits using MidInfrared Graphene Pla c2014/07/253 a We consider a quantum network of mid-infrared, graphene plasmons coupled to the hydrogen-like excited states of group-V donors in silicon. First, we show how to use plasmon-enhanced light-matter interactions to achieve single-shot spin readout of the donor qubits via optical excitation and electrical detection of the emitted plasmons. We then show how plasmons in high mobility graphene nanoribbons can be used to achieve high-fidelity, two-qubit gates and entanglement of distant Si donor qubits. The proposed device is readily compatible with existing technology and fabrication methods. 1 aGullans, Michael1 aTaylor, J., M. uhttp://arxiv.org/abs/1407.7035v101304nas a2200169 4500008004100000245009000041210006900131260001400200490000700214520080200221100001501023700001901038700001601057700001201073700001201085856003701097 2014 eng d00aSpin-orbit-coupled topological Fulde-Ferrell states of fermions in a harmonic trap 0 aSpinorbitcoupled topological FuldeFerrell states of fermions in  c2014/11/70 v903 a Motivated by recent experimental breakthroughs in generating spin-orbit coupling in ultracold Fermi gases using Raman laser beams, we present a systematic study of spin-orbit-coupled Fermi gases confined in a quasi-one-dimensional trap in the presence of an in-plane Zeeman field (which can be realized using a finite two-photon Raman detuning). We find that a topological Fulde-Ferrell state will emerge, featuring finite-momentum Cooper pairing and zero-energy Majorana excitations localized near the edge of the trap based on the self-consistent Bogoliubov-de Genes (BdG) equations. We find analytically the wavefunctions of the Majorana modes. Finally using the time-dependent BdG we show how the finite-momentum pairing field manifests itself in the expansion dynamics of the atomic cloud. 1 aJiang, Lei1 aTiesinga, Eite1 aLiu, Xia-Ji1 aHu, Hui1 aPu, Han uhttp://arxiv.org/abs/1404.6211v101470nas a2200205 4500008004100000245006500041210006400106260001500170300001400185490000800199520087200207100001701079700002201096700002001118700002101138700002301159700002501182700002001207856003701227 2013 eng d00aAll-Optical Switch and Transistor Gated by One Stored Photon0 aAllOptical Switch and Transistor Gated by One Stored Photon c2013/07/04 a768 - 7700 v3413 a The realization of an all-optical transistor where one 'gate' photon controls a 'source' light beam, is a long-standing goal in optics. By stopping a light pulse in an atomic ensemble contained inside an optical resonator, we realize a device in which one stored gate photon controls the resonator transmission of subsequently applied source photons. A weak gate pulse induces bimodal transmission distribution, corresponding to zero and one gate photons. One stored gate photon produces fivefold source attenuation, and can be retrieved from the atomic ensemble after switching more than one source photon. Without retrieval, one stored gate photon can switch several hundred source photons. With improved storage and retrieval efficiency, our work may enable various new applications, including photonic quantum gates, and deterministic multiphoton entanglement. 1 aChen, Wenlan1 aBeck, Kristin, M.1 aBücker, Robert1 aGullans, Michael1 aLukin, Mikhail, D.1 aTanji-Suzuki, Haruka1 aVuletic, Vladan uhttp://arxiv.org/abs/1401.3194v101734nas 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/1304.3407v202343nas a2200133 4500008004100000245010800041210006900149260001400218490000700232520189600239100001802135700001902153856003702172 2013 eng d00aFormation and decay of Bose-Einstein condensates in an excited band of a double-well optical lattice 0 aFormation and decay of BoseEinstein condensates in an excited ba c2013/9/120 v883 a We study the formation and collision-aided decay of an ultra-cold atomic Bose-Einstein condensate in the first excited band of a double-well 2D-optical lattice with weak harmonic confinement in the perpendicular $z$ direction. This lattice geometry is based on an experiment by Wirth et al. The double well is asymmetric, with the local ground state in the shallow well nearly degenerate with the first excited state of the adjacent deep well. We compare the band structure obtained from a tight-binding (TB) model with that obtained numerically using a plane wave basis. We find the TB model to be in quantitative agreement for the lowest two bands, qualitative for next two bands, and inadequate for even higher bands. The band widths of the excited bands are much larger than the harmonic oscillator energy spacing in the $z$ direction. We then study the thermodynamics of a non-interacting Bose gas in the first excited band. We estimate the condensate fraction and critical temperature, $T_c$, as functions of lattice parameters. For typical atom numbers, the critical energy $k_BT_c$, with $k_B$ the Boltzmann constant, is larger than the excited band widths and harmonic oscillator energy. Using conservation of total energy and atom number, we show that the temperature increases after the lattice transformation. Finally, we estimate the time scale for a two-body collision-aided decay of the condensate as a function of lattice parameters. The decay involves two processes, the dominant one in which both colliding atoms decay to the ground band, and the second involving excitation of one atom to a higher band. For this estimate, we have used TB wave functions for the lowest four bands, and numerical estimates for higher bands. The decay rate rapidly increases with lattice depth, but stays smaller than the tunneling rate between the $s$ and $p$ orbitals in adjacent wells. 1 aPaul, Saurabh1 aTiesinga, Eite uhttp://arxiv.org/abs/1308.4449v101256nas a2200121 4500008004100000245004400041210004200085260001500127520092000142100001601062700001901078856003701097 2013 eng d00aA noise inequality for classical forces0 anoise inequality for classical forces c2013/11/183 aLorentz invariance requires local interactions, with force laws such as the Coulomb interaction arising via virtual exchange of force carriers such as photons. Many have considered the possibility that, at long distances or large mass scales, this process changes in some way to lead to classical behavior. Here we hypothesize that classical behavior could be due to an inability of some force carriers to convey entanglement, a characteristic measure of nonlocal, quantum behavior. We then prove that there exists a local test that allows one to verify entanglement generation, falsifying our hypothesis. Crucially, we show that noise measurements can directly verify entanglement generation. This provides a step forward for a wide variety of experimental systems where traditional entanglement tests are challenging, including entanglement generation by gravity alone between macroscopic torsional oscillators. 1 aKafri, Dvir1 aTaylor, J., M. uhttp://arxiv.org/abs/1311.4558v101759nas a2200169 4500008004100000245008100041210006900122260001400191490000700205520124300212100002101455700001801476700001901494700002101513700001801534856003701552 2013 eng d00aPreparation of Non-equilibrium Nuclear Spin States in Double Quantum Dots 0 aPreparation of Nonequilibrium Nuclear Spin States in Double Quan c2013/7/150 v883 a We theoretically study the dynamic polarization of lattice nuclear spins in GaAs double quantum dots containing two electrons. In our prior work [Phys. Rev. Lett. 104, 226807 (2010)] we identified three regimes of long-term dynamics, 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. In particular, when the dots are different sizes we found that the Overhauser field becomes larger in the smaller dot. Here we present a detailed theoretical analysis of these problems including a model of the polarization dynamics and the development of a new numerical method to efficiently simulate semiclassical central-spin problems. When nuclear spin noise is included, the results agree with our prior work indicating that large difference fields and dark states are stable configurations, while the elimination of the difference field is unstable; however, in the absence of noise we find all three steady states are achieved depending on parameters. These results are in good agreement with dynamic nuclear polarization experiments in double quantum dots. 1 aGullans, Michael1 aKrich, J., J.1 aTaylor, J., M.1 aHalperin, B., I.1 aLukin, M., D. uhttp://arxiv.org/abs/1212.6953v302134nas a2200133 4500008004100000245008900041210006900130260001400199490000700213520170000220100001901920700002401939856003701963 2013 eng d00aQuadrature interferometry for nonequilibrium ultracold bosons in optical lattices 0 aQuadrature interferometry for nonequilibrium ultracold bosons in c2013/1/220 v873 a We develop an interferometric technique for making time-resolved measurements of field-quadrature operators for nonequilibrium ultracold bosons in optical lattices. The technique exploits the internal state structure of magnetic atoms to create two subsystems of atoms in different spin states and lattice sites. A Feshbach resonance turns off atom-atom interactions in one spin subsystem, making it a well-characterized reference state, while atoms in the other subsystem undergo nonequilibrium dynamics for a variable hold time. Interfering the subsystems via a second beam-splitting operation, time-resolved quadrature measurements on the interacting atoms are obtained by detecting relative spin populations. The technique can provide quadrature measurements for a variety of Hamiltonians and lattice geometries (e.g., cubic, honeycomb, superlattices), including systems with tunneling, spin-orbit couplings using artificial gauge fields, and higher-band effects. Analyzing the special case of a deep lattice with negligible tunneling, we obtain the time evolution of both quadrature observables and their fluctuations. As a second application, we show that the interferometer can be used to measure atom-atom interaction strengths with super-Heisenberg scaling n^(-3/2) in the mean number of atoms per lattice site n, and standard quantum limit scaling M^(-1/2) in the number of lattice sites M. In our analysis, we require M >> 1 and for realistic systems n is small, and therefore the scaling in total atom number N = nM is below the Heisenberg limit; nevertheless, measurements testing the scaling behaviors for interaction-based quantum metrologies should be possible in this system. 1 aTiesinga, Eite1 aJohnson, Philip, R. uhttp://arxiv.org/abs/1212.1193v201080nas 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/1304.3413v201244nas 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/1302.1933v101731nas a2200145 4500008004100000245007000041210006900111260001300180490000700193520128300200100002401483700002201507700001901529856003701548 2013 eng d00aSoliton dynamics of an atomic spinor condensate on a Ring Lattice0 aSoliton dynamics of an atomic spinor condensate on a Ring Lattic c2013/3/60 v873 a We study the dynamics of macroscopically-coherent matter waves of an ultra-cold atomic spin-one or spinor condensate on a ring lattice of six sites and demonstrate a novel type of spatio-temporal internal Josephson effect. Using a discrete solitary mode of uncoupled spin components as an initial condition, the time evolution of this many-body system is found to be characterized by two dominant frequencies leading to quasiperiodic dynamics at various sites. The dynamics of spatially-averaged and spin-averaged degrees of freedom, however, is periodic enabling an unique identification of the two frequencies. By increasing the spin-dependent atom-atom interaction strength we observe a resonance state, where the ratio of the two frequencies is a characteristic integer multiple and the spin-and-spatial degrees of freedom oscillate in "unison". Crucially, this resonant state is found to signal the onset to chaotic dynamics characterized by a broad band spectrum. In a ferromagnetic spinor condensate with attractive spin-dependent interactions, the resonance is accompanied by a transition from oscillatory- to rotational-type dynamics as the time evolution of the relative phase of the matter wave of the individual spin projections changes from bounded to unbounded. 1 aSatija, Indubala, I1 aPando, Carlos, L.1 aTiesinga, Eite uhttp://arxiv.org/abs/1301.5851v101428nas a2200193 4500008004100000245006800041210006700109260001300176490000800189520085100197100002401048700002501072700002201097700002201119700001801141700001901159700001901178856003701197 2013 eng d00aSpinor dynamics in an antiferromagnetic spin-1 thermal Bose gas0 aSpinor dynamics in an antiferromagnetic spin1 thermal Bose gas c2013/7/90 v1113 a We present experimental observations of coherent spin-population oscillations in a cold thermal, Bose gas of spin-1 sodium-23 atoms. The population oscillations in a multi-spatial-mode thermal gas have the same behavior as those observed in a single-spatial-mode antiferromagnetic spinor Bose Einstein condensate. We demonstrate this by showing that the two situations are described by the same dynamical equations, with a factor of two change in the spin-dependent interaction coefficient, which results from the change to particles with distinguishable momentum states in the thermal gas. We compare this theory to the measured spin population evolution after times up to a few hundreds of ms, finding quantitative agreement with the amplitude and period. We also measure the damping time of the oscillations as a function of magnetic field. 1 aPechkis, Hyewon, K.1 aWrubel, Jonathan, P.1 aSchwettmann, Arne1 aGriffin, Paul, F.1 aBarnett, Ryan1 aTiesinga, Eite1 aLett, Paul, D. uhttp://arxiv.org/abs/1306.4255v101029nas a2200121 4500008004100000245004700041210004700088260001500135520068500150100001600835700001900851856003700870 2012 eng d00aAlgorithmic Cooling of a Quantum Simulator0 aAlgorithmic Cooling of a Quantum Simulator c2012/07/303 aControlled quantum mechanical devices provide a means of simulating more complex quantum systems exponentially faster than classical computers. Such "quantum simulators" rely heavily upon being able to prepare the ground state of Hamiltonians, whose properties can be used to calculate correlation functions or even the solution to certain classical computations. While adiabatic preparation remains the primary means of producing such ground states, here we provide a different avenue of preparation: cooling to the ground state via simulated dissipation. This is in direct analogy to contemporary efforts to realize generalized forms of simulated annealing in quantum systems. 1 aKafri, Dvir1 aTaylor, J., M. uhttp://arxiv.org/abs/1207.7111v101318nas a2200145 4500008004100000245008900041210006900130260001300199490000800212520084800220100002201068700001901090700002601109856003701135 2012 eng d00aAnisotropy induced Feshbach resonances in a quantum dipolar gas of magnetic atoms 0 aAnisotropy induced Feshbach resonances in a quantum dipolar gas  c2012/9/70 v1093 a We explore the anisotropic nature of Feshbach resonances in the collision between ultracold magnetic submerged-shell dysprosium atoms, which can only occur due to couplings to rotating bound states. This is in contrast to well-studied alkali-metal atom collisions, where most Feshbach resonances are hyperfine induced and due to rotation-less bound states. Our novel first-principle coupled-channel calculation of the collisions between open-4f-shell spin-polarized bosonic dysprosium reveals a striking correlation between the anisotropy due to magnetic dipole-dipole and electrostatic interactions and the Feshbach spectrum as a function of an external magnetic field. Over a 20 mT magnetic field range we predict about a dozen Feshbach resonances and show that the resonance locations are exquisitely sensitive to the dysprosium isotope. 1 aPetrov, Alexander1 aTiesinga, Eite1 aKotochigova, Svetlana uhttp://arxiv.org/abs/1203.4172v102074nas a2200157 4500008004100000245008100041210006900122260001500191490000700206520159700213100001501810700002001825700001901845700001501864856003701879 2012 eng d00aThe equilibrium states of open quantum systems in the strong coupling regime0 aequilibrium states of open quantum systems in the strong couplin c2012/12/260 v863 aIn this work we investigate the late-time stationary states of open quantum systems coupled to a thermal reservoir in the strong coupling regime. In general such systems do not necessarily relax to a Boltzmann distribution if the coupling to the thermal reservoir is non-vanishing or equivalently if the relaxation timescales are finite. Using a variety of non-equilibrium formalisms valid for non-Markovian processes, we show that starting from a product state of the closed system = system + environment, with the environment in its thermal state, the open system which results from coarse graining the environment will evolve towards an equilibrium state at late-times. This state can be expressed as the reduced state of the closed system thermal state at the temperature of the environment. For a linear (harmonic) system and environment, which is exactly solvable, we are able to show in a rigorous way that all multi-time correlations of the open system evolve towards those of the closed system thermal state. Multi-time correlations are especially relevant in the non-Markovian regime, since they cannot be generated by the dynamics of the single-time correlations. For more general systems, which cannot be exactly solved, we are able to provide a general proof that all single-time correlations of the open system evolve to those of the closed system thermal state, to first order in the relaxation rates. For the special case of a zero-temperature reservoir, we are able to explicitly construct the reduced closed system thermal state in terms of the environmental correlations. 1 aSubasi, Y.1 aFleming, C., H.1 aTaylor, J., M.1 aHu, B., L. uhttp://arxiv.org/abs/1206.2707v101154nas a2200205 4500008004100000245004700041210004700088260001400135490000800149520061400157100002100771700001500792700001800807700001400825700002100839700001800860700001500878700001800893856003700911 2012 eng d00aNanoplasmonic Lattices for Ultracold atoms0 aNanoplasmonic Lattices for Ultracold atoms c2012/12/60 v1093 a We propose to use sub-wavelength confinement of light associated with the near field of plasmonic systems to create nanoscale optical lattices for ultracold atoms. Our approach combines the unique coherence properties of isolated atoms with the sub-wavelength manipulation and strong light-matter interaction associated with nano-plasmonic systems. It allows one to considerably increase the energy scales in the realization of Hubbard models and to engineer effective long-range interactions in coherent and dissipative many-body dynamics. Realistic imperfections and potential applications are discussed. 1 aGullans, Michael1 aTiecke, T.1 aChang, D., E.1 aFeist, J.1 aThompson, J., D.1 aCirac, J., I.1 aZoller, P.1 aLukin, M., D. uhttp://arxiv.org/abs/1208.6293v301226nas a2200169 4500008004100000245007000041210006900111260001400180490000800194520072500202100001900927700001400946700002000960700002000980700001901000856003701019 2012 eng d00aQuantum interface between an electrical circuit and a single atom0 aQuantum interface between an electrical circuit and a single ato c2012/3/300 v1083 aWe show how to bridge the divide between atomic systems and electronic devices by engineering a coupling between the motion of a single ion and the quantized electric field of a resonant circuit. Our method can be used to couple the internal state of an ion to the quantized circuit with the same speed as the internal-state coupling between two ions. All the well-known quantum information protocols linking ion internal and motional states can be converted to protocols between circuit photons and ion internal states. Our results enable quantum interfaces between solid state qubits, atomic qubits, and light, and lay the groundwork for a direct quantum connection between electrical and atomic metrology standards. 1 aKielpinski, D.1 aKafri, D.1 aWoolley, M., J.1 aMilburn, G., J.1 aTaylor, J., M. uhttp://arxiv.org/abs/1111.5999v101195nas a2200157 4500008004100000245006200041210006200103260001300165490000700178520072500185100002200910700001900932700002600951700002300977856003701000 2012 eng d00aResonant control of polar molecules in an optical lattice0 aResonant control of polar molecules in an optical lattice c2012/2/80 v853 a We study the resonant control of two nonreactive polar molecules in an optical lattice site, focussing on the example of RbCs. Collisional control can be achieved by tuning bound states of the intermolecular dipolar potential, by varying the applied electric field or trap frequency. We consider a wide range of electric fields and trapping geometries, showing that a three-dimensional optical lattice allows for significantly wider avoided crossings than free space or quasi-two dimensional geometries. Furthermore, we find that dipolar confinement induced resonances can be created with reasonable trapping frequencies and electric fields, and have widths that will enable useful control in forthcoming experiments. 1 aHanna, Thomas, M.1 aTiesinga, Eite1 aMitchell, William, F.1 aJulienne, Paul, S. uhttp://arxiv.org/abs/1111.0227v101233nas a2200157 4500008004100000245006500041210006300106260001400169490000800183520075800191100002300949700002200972700002400994700002001018856003701038 2012 eng d00aSteady-state many-body entanglement of hot reactive fermions0 aSteadystate manybody entanglement of hot reactive fermions c2012/12/40 v1093 a Entanglement is typically created via systematic intervention in the time evolution of an initially unentangled state, which can be achieved by coherent control, carefully tailored non-demolition measurements, or dissipation in the presence of properly engineered reservoirs. In this paper we show that two-component Fermi gases at ~\mu K temperatures naturally evolve, in the presence of reactive two-body collisions, into states with highly entangled (Dicke-type) spin wavefunctions. The entanglement is a steady-state property that emerges---without any intervention---from uncorrelated initial states, and could be used to improve the accuracy of spectroscopy in experiments with fermionic alkaline earth atoms or fermionic groundstate molecules. 1 aFoss-Feig, Michael1 aDaley, Andrew, J.1 aThompson, James, K.1 aRey, Ana, Maria uhttp://arxiv.org/abs/1207.4741v101241nas 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/1103.3513v301407nas a2200157 4500008004100000245006700041210006700108260001400175490000700189520094200196100002201138700001701160700001901177700001601196856003701212 2011 eng d00aFast and robust quantum computation with ionic Wigner crystals0 aFast and robust quantum computation with ionic Wigner crystals c2011/4/150 v833 aWe present a detailed analysis of the modulated-carrier quantum phase gate implemented with Wigner crystals of ions confined in Penning traps. We elaborate on a recent scheme, proposed by two of the authors, to engineer two-body interactions between ions in such crystals. We analyze for the first time the situation in which the cyclotron (w_c) and the crystal rotation (w_r) frequencies do not fulfill the condition w_c=2w_r. It is shown that even in the presence of the magnetic field in the rotating frame the many-body (classical) Hamiltonian describing small oscillations from the ion equilibrium positions can be recast in canonical form. As a consequence, we are able to demonstrate that fast and robust two-qubit gates are achievable within the current experimental limitations. Moreover, we describe a realization of the state-dependent sign-changing dipole forces needed to realize the investigated quantum computing scheme. 1 aBaltrusch, J., D.1 aNegretti, A.1 aTaylor, J., M.1 aCalarco, T. uhttp://arxiv.org/abs/1011.5616v200913nas a2200145 4500008004100000245004700041210004700088260001300135490000700148520050500155100002600660700001900686700002500705856003700730 2011 eng d00aInterferometry with Synthetic Gauge Fields0 aInterferometry with Synthetic Gauge Fields c2011/3/30 v833 aWe propose a compact atom interferometry scheme for measuring weak, time-dependent accelerations. Our proposal uses an ensemble of dilute trapped bosons with two internal states that couple to a synthetic gauge field with opposite charges. The trapped gauge field couples spin to momentum to allow time dependent accelerations to be continuously imparted on the internal states. We generalize this system to reduce noise and estimate the sensitivity of such a system to be S~10^-7 m / s^2 / Hz^1/2. 1 aAnderson, Brandon, M.1 aTaylor, J., M.1 aGalitski, Victor, M. uhttp://arxiv.org/abs/1008.3910v201053nas 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/1108.2035v101279nas 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/1104.1722v101304nas a2200145 4500008004100000245006900041210006900110260001300179490000700192520086300199100001801062700002201080700001901102856003701121 2011 eng d00aSuperradiance of cold atoms coupled to a superconducting circuit0 aSuperradiance of cold atoms coupled to a superconducting circuit c2011/6/60 v833 a We investigate superradiance of an ensemble of atoms coupled to an integrated superconducting LC-circuit. Particular attention is paid to the effect of inhomogeneous coupling constants. Combining perturbation theory in the inhomogeneity and numerical simulations we show that inhomogeneous coupling constants can significantly affect the superradiant relaxation process. Incomplete relaxation terminating in "dark states" can occur, from which the only escape is through individual spontaneous emission on a much longer time scale. The relaxation dynamics can be significantly accelerated or retarded, depending on the distribution of the coupling constants. On the technical side, we also generalize the previously known propagator of superradiance for identical couplings in the completely symmetric sector to the full exponentially large Hilbert space. 1 aBraun, Daniel1 aHoffman, Jonathan1 aTiesinga, Eite uhttp://arxiv.org/abs/1101.5300v101255nas a2200133 4500008004100000245010500041210006900146260001400215490000700229520081400236100001501050700001901065856003701084 2011 eng d00aUnified approach to topological quantum computation with anyons: From qubit encoding to Toffoli gate0 aUnified approach to topological quantum computation with anyons  c2011/7/260 v843 aTopological quantum computation may provide a robust approach for encoding and manipulating information utilizing the topological properties of anyonic quasi-particle excitations. We develop an efficient means to map between dense and sparse representations of quantum information (qubits) and a simple construction of multi-qubit gates, for all anyon models from Chern-Simons-Witten SU(2)$_k$ theory that support universal quantum computation by braiding ($k\geq 3,\ k \neq 4$). In the process, we show how the constructions of topological quantum memory and gates for $k=2,4$ connect naturally to those for $k\geq 3,\ k \neq 4$, unifying these concepts in a simple framework. Furthermore, we illustrate potential extensions of these ideas to other anyon models outside of Chern-Simons-Witten field theory. 1 aXu, Haitan1 aTaylor, J., M. uhttp://arxiv.org/abs/1001.4085v201723nas a2200157 4500008004100000245008700041210006900128260001500197300001100212490000700223520123400230100002201464700001901486700002301505856003701528 2010 eng d00aCreation and manipulation of Feshbach resonances with radio-frequency radiation 0 aCreation and manipulation of Feshbach resonances with radiofrequ c2010/08/12 a0830310 v123 a We present a simple technique for studying collisions of ultracold atoms in the presence of a magnetic field and radio-frequency radiation (rf). Resonant control of scattering properties can be achieved by using rf to couple a colliding pair of atoms to a bound state. We show, using the example of 6Li, that in some ranges of rf frequency and magnetic field this can be done without giving rise to losses. We also show that halo molecules of large spatial extent require much less rf power than deeply bound states. Another way to exert resonant control is with a set of rf-coupled bound states, linked to the colliding pair through the molecular interactions that give rise to magnetically tunable Feshbach resonances. This was recently demonstrated for 87Rb [Kaufman et al., Phys. Rev. A 80:050701(R), 2009]. We examine the underlying atomic and molecular physics which made this possible. Lastly, we consider the control that may be exerted over atomic collisions by placing atoms in superpositions of Zeeman states, and suggest that it could be useful where small changes in scattering length are required. We suggest other species for which rf and magnetic field control could together provide a useful tuning mechanism. 1 aHanna, Thomas, M.1 aTiesinga, Eite1 aJulienne, Paul, S. uhttp://arxiv.org/abs/1004.0636v101401nas 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/1003.4508v200782nas 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.html01169nas a2200169 4500008004100000245004300041210004300084260001400127300001600141490000700157520072600164100001600890700001800906700001900924700001900943856003700962 2010 eng d00aFeshbach Resonances in Ultracold Gases0 aFeshbach Resonances in Ultracold Gases c2010/4/29 a1225 - 12860 v823 a Feshbach resonances are the essential tool to control the interaction between atoms in ultracold quantum gases. They have found numerous experimental applications, opening up the way to important breakthroughs. This Review broadly covers the phenomenon of Feshbach resonances in ultracold gases and their main applications. This includes the theoretical background and models for the description of Feshbach resonances, the experimental methods to find and characterize the resonances, a discussion of the main properties of resonances in various atomic species and mixed atomic species systems, and an overview of key experiments with atomic Bose-Einstein condensates, degenerate Fermi gases, and ultracold molecules. 1 aChin, Cheng1 aGrimm, Rudolf1 aJulienne, Paul1 aTiesinga, Eite uhttp://arxiv.org/abs/0812.1496v201137nas 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/0906.2150v101547nas a2200157 4500008004100000245009000041210006900131260001500200300001100215490000700226520105100233100002601284700001901310700002301329856003701352 2009 eng d00aMulti-channel modelling of the formation of vibrationally cold polar KRb molecules 0 aMultichannel modelling of the formation of vibrationally cold po c2009/05/14 a0550430 v113 a We describe the theoretical advances that influenced the experimental creation of vibrationally and translationally cold polar $^{40}$K$^{87}$Rb molecules \cite{nphys08,science08}. Cold molecules were created from very-weakly bound molecules formed by magnetic field sweeps near a Feshbach resonance in collisions of ultra-cold $^{40}$K and $^{87}$Rb atoms. Our analysis include the multi-channel bound-state calculations of the hyperfine and Zeeman mixed X$^1\Sigma^+$ and a$^3\Sigma^+$ vibrational levels. We find excellent agreement with the hyperfine structure observed in experimental data. In addition, we studied the spin-orbit mixing in the intermediate state of the Raman transition. This allowed us to investigate its effect on the vibrationally-averaged transition dipole moment to the lowest ro-vibrational level of the X$^1\Sigma^+$ state. Finally, we obtained an estimate of the polarizability of the initial and final ro-vibrational states of the Raman transition near frequencies relevant for optical trapping of the molecules. 1 aKotochigova, Svetlana1 aTiesinga, Eite1 aJulienne, Paul, S. uhttp://arxiv.org/abs/0901.1486v101306nas 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/0906.2110v101221nas a2200145 4500008004100000245006600041210006600107260001400173490000700187520078000194100002200974700001900996700002301015856003701038 2009 eng d00aPrediction of Feshbach resonances from three input parameters0 aPrediction of Feshbach resonances from three input parameters c2009/4/300 v793 a We have developed a model of Feshbach resonances in gases of ultracold alkali metal atoms using the ideas of multichannel quantum defect theory. Our model requires just three parameters describing the interactions - the singlet and triplet scattering lengths, and the long range van der Waals coefficient - in addition to known atomic properties. Without using any further details of the interactions, our approach can accurately predict the locations of resonances. It can also be used to find the singlet and triplet scattering lengths from measured resonance data. We apply our technique to $^{6}$Li--$^{40}$K and $^{40}$K--$^{87}$Rb scattering, obtaining good agreement with experimental results, and with the more computationally intensive coupled channels technique. 1 aHanna, Thomas, M.1 aTiesinga, Eite1 aJulienne, Paul, S. uhttp://arxiv.org/abs/0903.0884v201274nas 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/0902.3189v100937nas a2200145 4500008004100000245005000041210004600091260001500137520051500152100002100667700002300688700002300711700002000734856003700754 2009 eng d00aThe quantum query complexity of certification0 aquantum query complexity of certification c2009/03/063 a We study the quantum query complexity of finding a certificate for a d-regular, k-level balanced NAND formula. Up to logarithmic factors, we show that the query complexity is Theta(d^{(k+1)/2}) for 0-certificates, and Theta(d^{k/2}) for 1-certificates. In particular, this shows that the zero-error quantum query complexity of evaluating such formulas is O(d^{(k+1)/2}) (again neglecting a logarithmic factor). Our lower bound relies on the fact that the quantum adversary method obeys a direct sum theorem. 1 aAmbainis, Andris1 aChilds, Andrew, M.1 aLe Gall, François1 aTani, Seiichiro uhttp://arxiv.org/abs/0903.1291v201381nas a2200145 4500008004100000245007000041210006900111260001400180490000700194520093200201100002301133700001901156700002301175856003701198 2008 eng d00aAvoided crossings between bound states of ultracold Cesium dimers0 aAvoided crossings between bound states of ultracold Cesium dimer c2008/11/50 v783 a We present an efficient new computational method for calculating the binding energies of the bound states of ultracold alkali-metal dimers in the presence of magnetic fields. The method is based on propagation of coupled differential equations and does not use a basis set for the interatomic distance coordinate. It is much more efficient than the previous method based on a radial basis set and allows many more spin channels to be included. This is particularly important in the vicinity of avoided crossings between bound states. We characterize a number of different avoided crossings in Cs_2 and compare our converged calculations with experimental results. Small but significant discrepancies are observed in both crossing strengths and level positions, especially for levels with l symmetry (rotational angular momentum L=8). The discrepancies should allow the development of improved potential models in the future. 1 aHutson, Jeremy, M.1 aTiesinga, Eite1 aJulienne, Paul, S. uhttp://arxiv.org/abs/0806.2583v101409nas a2200193 4500008004100000245006800041210006800109260001400177490000800191520083700199100001701036700002501053700001601078700002001094700002201114700001901136700002301155856003701178 2008 eng d00aCoherence of an optically illuminated single nuclear spin qubit0 aCoherence of an optically illuminated single nuclear spin qubit c2008/2/190 v1003 aWe investigate the coherence properties of individual nuclear spin quantum bits in diamond [Dutt et al., Science, 316, 1312 (2007)] when a proximal electronic spin associated with a nitrogen-vacancy (NV) center is being interrogated by optical radiation. The resulting nuclear spin dynamics are governed by time-dependent hyperfine interaction associated with rapid electronic transitions, which can be described by a spin-fluctuator model. We show that due to a process analogous to motional averaging in nuclear magnetic resonance, the nuclear spin coherence can be preserved after a large number of optical excitation cycles. Our theoretical analysis is in good agreement with experimental results. It indicates a novel approach that could potentially isolate the nuclear spin system completely from the electronic environment. 1 aJiang, Liang1 aDutt, M., V. Gurudev1 aTogan, Emre1 aChildress, Lily1 aCappellaro, Paola1 aTaylor, J., M.1 aLukin, Mikhail, D. uhttp://arxiv.org/abs/0707.1341v201250nas a2200229 4500008004100000245006800041210006700109260001400176300001400190490000600204520061800210100001900828700001900847700001800866700001400884700001500898700001900913700001500932700001800947700001800965856003700983 2008 eng d00aHigh-sensitivity diamond magnetometer with nanoscale resolution0 aHighsensitivity diamond magnetometer with nanoscale resolution c2008/9/14 a810 - 8160 v43 aWe present a novel approach to the detection of weak magnetic fields that takes advantage of recently developed techniques for the coherent control of solid-state electron spin quantum bits. Specifically, we investigate a magnetic sensor based on Nitrogen-Vacancy centers in room-temperature diamond. We discuss two important applications of this technique: a nanoscale magnetometer that could potentially detect precession of single nuclear spins and an optical magnetic field imager combining spatial resolution ranging from micrometers to millimeters with a sensitivity approaching few femtotesla/Hz$^{1/2}$. 1 aTaylor, J., M.1 aCappellaro, P.1 aChildress, L.1 aJiang, L.1 aBudker, D.1 aHemmer, P., R.1 aYacoby, A.1 aWalsworth, R.1 aLukin, M., D. uhttp://arxiv.org/abs/0805.1367v101777nas 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/0806.4711v201333nas 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/0805.3680v101425nas a2200169 4500008004100000245006800041210006700109260001400176490000700190520091100197100002701108700001801135700001901153700002301172700002301195856003701218 2008 eng d00aTunneling phase gate for neutral atoms in a double-well lattice0 aTunneling phase gate for neutral atoms in a doublewell lattice c2008/5/120 v773 a We propose a new two--qubit phase gate for ultra--cold atoms confined in an experimentally realized tilted double--well optical lattice [Sebby--Strabley et al., Phys. Rev. A {\bf 73} 033605 (2006)]. Such a lattice is capable of confining pairs of atoms in a two--dimensional array of double--well potentials where control can be exercised over the barrier height and the energy difference of the minima of the two wells (known as the ``tilt''). The four lowest single--particle motional states consist of two pairs of motional states in which each pair is localized on one side of the central barrier, allowing for two atoms confined in such a lattice to be spatially separated qubits. We present a time--dependent scheme to manipulate the tilt to induce tunneling oscillations which produce a collisional phase gate. Numerical simulations demonstrate that this gate can be performed with high fidelity. 1 aStrauch, Frederick, W.1 aEdwards, Mark1 aTiesinga, Eite1 aWilliams, Carl, J.1 aClark, Charles, W. uhttp://arxiv.org/abs/0712.1856v101063nas a2200145 4500008004100000245005700041210005500098260001300153490000800166520064500174100001900819700001900838700002300857856003700880 2008 eng d00aTwo-body transients in coupled atomic-molecular BECs0 aTwobody transients in coupled atomicmolecular BECs c2008/3/30 v1003 a We discuss the dynamics of an atomic Bose-Einstein condensate when pairs of atoms are converted into molecules by single-color photoassociation. Three main regimes are found and it is shown that they can be understood on the basis of time-dependent two-body theory. In particular, the so-called rogue dissociation regime [Phys. Rev. Lett., 88, 090403 (2002)], which has a density-dependent limit on the photoassociation rate, is identified with a transient regime of the two-atom dynamics exhibiting universal properties. Finally, we illustrate how these regimes could be explored by photoassociating condensates of alkaline-earth atoms. 1 aNaidon, Pascal1 aTiesinga, Eite1 aJulienne, Paul, S. uhttp://arxiv.org/abs/0707.2963v200962nas a2200133 4500008004100000245005100041210005100092260001500143490000700158520059100165100001900756700001600775856003700791 2008 eng d00aWigner crystals of ions as quantum hard drives0 aWigner crystals of ions as quantum hard drives c2008/12/180 v783 aAtomic systems in regular lattices are intriguing systems for implementing ideas in quantum simulation and information processing. Focusing on laser cooled ions forming Wigner crystals in Penning traps, we find a robust and simple approach to engineering non-trivial 2-body interactions sufficient for universal quantum computation. We then consider extensions of our approach to the fast generation of large cluster states, and a non-local architecture using an asymmetric entanglement generation procedure between a Penning trap system and well-established linear Paul trap designs. 1 aTaylor, J., M.1 aCalarco, T. uhttp://arxiv.org/abs/0706.1951v101051nas a2200133 4500008004100000245010600041210006900147260001500216520058800231100001900819700001900838700002300857856003700880 2007 eng d00aCoherent, adiabatic and dissociation regimes in coupled atomic-molecular Bose-Einstein condensates 0 aCoherent adiabatic and dissociation regimes in coupled atomicmol c2007/11/023 a We discuss the dynamics of a Bose-Einstein condensate of atoms which is suddenly coupled to a condensate of molecules by an optical or magnetic Feshbach resonance. Three limiting regimes are found and can be understood from the transient dynamics occuring for each pair of atoms. This transient dynamics can be summarised into a time-dependent shift and broadening of the molecular state. A simple Gross-Pitaevskii picture including this shift and broadening is proposed to describe the system in the three regimes. Finally, we suggest how to explore these regimes experimentally. 1 aNaidon, Pascal1 aTiesinga, Eite1 aJulienne, Paul, S. uhttp://arxiv.org/abs/0711.0397v201036nas 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/0607140v201388nas a2200145 4500008004100000245009200041210006900133260001300202490000700215520092500222100001401147700001901161700001801180856004401198 2007 eng d00aA fast and robust approach to long-distance quantum communication with atomic ensembles0 afast and robust approach to longdistance quantum communication w c2007/7/20 v763 aQuantum repeaters create long-distance entanglement between quantum systems while overcoming difficulties such as the attenuation of single photons in a fiber. Recently, an implementation of a repeater protocol based on single qubits in atomic ensembles and linear optics has been proposed [Nature 414, 413 (2001)]. Motivated by rapid experimental progress towards implementing that protocol, here we develop a more efficient scheme compatible with active purification of arbitrary errors. Using similar resources as the earlier protocol, our approach intrinsically purifies leakage out of the logical subspace and all errors within the logical subspace, leading to greatly improved performance in the presence of experimental inefficiencies. Our analysis indicates that our scheme could generate approximately one pair per 3 minutes over 1280 km distance with fidelity (F>78%) sufficient to violate Bell's inequality. 1 aJiang, L.1 aTaylor, J., M.1 aLukin, M., D. uhttp://arxiv.org/abs/quant-ph/0609236v300956nas a2200109 4500008004100000245006300041210006100104260001500165520061000180100001900790856003700809 2007 eng d00aA quantum dot implementation of the quantum NAND algorithm0 aquantum dot implementation of the quantum NAND algorithm c2007/08/103 aWe propose a physical implementation of the quantum NAND tree evaluation algorithm. Our approach, based on continuous time quantum walks, uses the wave interference of a single electron in a heirarchical set of tunnel coupled quantum dots. We find that the query complexity of the NAND tree evaluation does not suffer strongly from disorder and dephasing, nor is it directly limited by temperature or restricted dimensionality for 2-d structures. Finally, we suggest a potential application of this algorithm to the efficient determination of high-order correlation functions of complex quantum systems. 1 aTaylor, J., M. uhttp://arxiv.org/abs/0708.1484v101375nas 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/0602470v200966nas a2200121 4500008004100000245008500041210006900126260001500195520055300210100001900763700001800782856004400800 2006 eng d00aCavity quantum electrodynamics with semiconductor double-dot molecules on a chip0 aCavity quantum electrodynamics with semiconductor doubledot mole c2006/05/053 aWe describe a coherent control technique for coupling electron spin states associated with semiconductor double-dot molecule to a microwave stripline resonator on a chip. We identify a novel regime of operation in which strong interaction between a molecule and a resonator can be achieved with minimal decoherence, reaching the so-called strong coupling regime of cavity QED. We describe potential applications of such a system, including low-noise coherent electrical control, fast QND measurements of spin states, and long-range spin coupling. 1 aTaylor, J., M.1 aLukin, M., D. uhttp://arxiv.org/abs/cond-mat/0605144v101138nas a2200157 4500008004100000245007600041210006900117260001400186490000700200520065300207100001800860700001900878700002100897700001800918856004400936 2006 eng d00aFault-tolerant Quantum Communication with Minimal Physical Requirements0 aFaulttolerant Quantum Communication with Minimal Physical Requir c2006/2/230 v963 aWe describe a novel protocol for a quantum repeater which enables long distance quantum communication through realistic, lossy photonic channels. Contrary to previous proposals, our protocol incorporates active purification of arbitrary errors at each step of the protocol using only two qubits at each repeater station. Because of these minimal physical requirements, the present protocol can be realized in simple physical systems such as solid-state single photon emitters. As an example, we show how nitrogen vacancy color centers in diamond can be used to implement the protocol, using the nuclear and electronic spin to form the two qubits. 1 aChildress, L.1 aTaylor, J., M.1 aSorensen, A., S.1 aLukin, M., D. uhttp://arxiv.org/abs/quant-ph/0410123v301484nas a2200121 4500008004100000245007100041210006900112260001500181520108500196100001901281700001801300856004401318 2005 eng d00aDephasing of quantum bits by a quasi-static mesoscopic environment0 aDephasing of quantum bits by a quasistatic mesoscopic environmen c2005/12/073 aWe examine coherent processes in a two-state quantum system that is strongly coupled to a mesoscopic spin bath and weakly coupled to other environmental degrees of freedom. Our analysis is specifically aimed at understanding the quantum dynamics of solid-state quantum bits such as electron spins in semiconductor structures and superconducting islands. The role of mesoscopic degrees of freedom with long correlation times (local degrees of freedom such as nuclear spins and charge traps) in qubit-related dephasing is discussed in terms of a quasi-static bath. A mathemat- ical framework simultaneously describing coupling to the slow mesoscopic bath and a Markovian environment is developed and the dephasing and decoherence properties of the total system are investigated. The model is applied to several specific examples with direct relevance to current ex- periments. Comparisons to experiments suggests that such quasi-static degrees of freedom play an important role in current qubit implementations. Several methods of mitigating the bath-induced error are considered. 1 aTaylor, J., M.1 aLukin, M., D. uhttp://arxiv.org/abs/quant-ph/0512059v201771nas a2200157 4500008004100000245012200041210006900163260001500232490000700247520123500254100002201489700001901511700002101530700001801551856004401569 2005 eng d00aFault-tolerant quantum repeaters with minimal physical resources, and implementations based on single photon emitters0 aFaulttolerant quantum repeaters with minimal physical resources  c2005/11/280 v723 aWe analyze a novel method that uses fixed, minimal physical resources to achieve generation and nested purification of quantum entanglement for quantum communication over arbitrarily long distances, and discuss its implementation using realistic photon emitters and photonic channels. In this method, we use single photon emitters with two internal degrees of freedom formed by an electron spin and a nuclear spin to build intermediate nodes in a quantum channel. State-selective fluorescence is used for probabilistic entanglement generation between electron spins in adjacent nodes. We analyze in detail several approaches which are applicable to realistic, homogeneously broadened single photon emitters. Furthermore, the coupled electron and nuclear spins can be used to efficiently implement entanglement swapping and purification. We show that these techniques can be combined to generate high-fidelity entanglement over arbitrarily long distances. We present a specific protocol that functions in polynomial time and tolerates percent-level errors in entanglement fidelity and local operations. The scheme has the lowest requirements on physical resources of any current scheme for fully fault-tolerant quantum repeaters. 1 aChildress, L., I.1 aTaylor, J., M.1 aSorensen, A., S.1 aLukin, M., D. uhttp://arxiv.org/abs/quant-ph/0502112v101042nas a2200157 4500008004100000245006600041210006500107260001500172490000700187520057000194100001200764700001900776700002300795700002300818856004300841 2005 eng d00aMultichannel quantum-defect theory for slow atomic collisions0 aMultichannel quantumdefect theory for slow atomic collisions c2005/10/280 v723 a We present a multichannel quantum-defect theory for slow atomic collisions that takes advantages of the analytic solutions for the long-range potential, and both the energy and the angular-momentum insensitivities of the short-range parameters. The theory provides an accurate and complete account of scattering processes, including shape and Feshbach resonances, in terms of a few parameters such as the singlet and the triplet scattering lengths. As an example, results for $^{23}$Na-$^{23}$Na scattering are presented and compared close-coupling calculations. 1 aGao, Bo1 aTiesinga, Eite1 aWilliams, Carl, J.1 aJulienne, Paul, S. uhttp://arxiv.org/abs/physics/0508060v101196nas 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/0503255v201059nas a2200145 4500008004100000245006200041210006100103260001400164490000700178520062000185100002200805700001900827700002300846856004400869 2005 eng d00aSpontaneous dissociation of long-range Feshbach molecules0 aSpontaneous dissociation of longrange Feshbach molecules c2005/1/180 v943 a We study the spontaneous dissociation of diatomic molecules produced in cold atomic gases via magnetically tunable Feshbach resonances. We provide a universal formula for the lifetime of these molecules that relates their decay to the scattering length and the loss rate constant for inelastic spin relaxation. Our universal treatment as well as our exact coupled channels calculations for $^{85}$Rb dimers predict a suppression of the decay over several orders of magnitude when the scattering length is increased. Our predictions are in good agreement with recent measurements of the lifetime of $^{85}$Rb$_2$. 1 aKoehler, Thorsten1 aTiesinga, Eite1 aJulienne, Paul, S. uhttp://arxiv.org/abs/cond-mat/0408387v202281nas a2200181 4500008004100000245009200041210006900133260001500202300001600217490000700233520170600240100002101946700002201967700002401989700001902013700002302032856004402055 2004 eng d00aAdiabatic association of ultracold molecules via magnetic field tunable interactions 0 aAdiabatic association of ultracold molecules via magnetic field  c2004/09/14 a3457 - 35000 v373 a We consider in detail the situation of applying a time dependent external magnetic field to a 87Rb atomic Bose-Einstein condensate held in a harmonic trap, in order to adiabatically sweep the interatomic interactions across a Feshbach resonance to produce diatomic molecules. To this end, we introduce a minimal two-body Hamiltonian depending on just five measurable parameters of a Feshbach resonance, which accurately determines all low energy binary scattering observables, in particular, the molecular conversion efficiency of just two atoms. Based on this description of the microscopic collision phenomena, we use the many-body theory of T. Koehler and K. Burnett [Phys. Rev. A 65, 033601 (2002)] to study the efficiency of the association of molecules in a 87Rb Bose-Einstein condensate during a linear passage of the magnetic field strength across the 100 mT Feshbach resonance. We explore different, experimentally accessible, parameter regimes, and compare the predictions of Landau-Zener, configuration interaction, and two level mean field calculations with those of the microscopic many-body approach. Our comparative studies reveal a remarkable insensitivity of the molecular conversion efficiency with respect to both the details of the microscopic binary collision physics and the coherent nature of the Bose-Einstein condensed gas, provided that the magnetic field strength is varied linearly. We provide the reasons for this universality of the molecular production achieved by linear ramps of the magnetic field strength, and identify the Landau-Zener coefficient determined by F.H. Mies et al. [Phys. Rev. A 61, 022721 (2000)] as the main parameter that controls the efficiency. 1 aGoral, Krzysztof1 aKoehler, Thorsten1 aGardiner, Simon, A.1 aTiesinga, Eite1 aJulienne, Paul, S. uhttp://arxiv.org/abs/cond-mat/0312178v501230nas a2200193 4500008004100000245007800041210006900119260001500188520065600203100001900859700001500878700001500893700001600908700001800924700001500942700001800957700001700975856004400992 2004 eng d00aQuantum information processing using localized ensembles of nuclear spins0 aQuantum information processing using localized ensembles of nucl c2004/07/233 aWe describe a technique for quantum information processing based on localized en sembles of nuclear spins. A qubit is identified as the presence or absence of a collective excitation of a mesoscopic ensemble of nuclear spins surrounding a single quantum dot. All single and two-qubit operations can be effected using hyperfine interactions and single-electron spin rotations, hence the proposed scheme avoids gate errors arising from entanglement between spin and orbital degrees of freedom. Ultra-long coherence times of nuclear spins suggest that this scheme could be particularly well suited for applications where long lived memory is essential. 1 aTaylor, J., M.1 aGiedke, G.1 aChrist, H.1 aParedes, B.1 aCirac, J., I.1 aZoller, P.1 aLukin, M., D.1 aImamoglu, A. uhttp://arxiv.org/abs/cond-mat/0407640v201386nas 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/0405097v101129nas a2200145 4500008004100000245007400041210006900115260001500184490000700199520067900206100001900885700001700904700001800921856004400939 2003 eng d00aControlling a mesoscopic spin environment by quantum bit manipulation0 aControlling a mesoscopic spin environment by quantum bit manipul c2003/12/100 v913 aWe present a unified description of cooling and manipulation of a mesoscopic bath of nuclear spins via coupling to a single quantum system of electronic spin (quantum bit). We show that a bath cooled by the quantum bit rapidly saturates. Although the resulting saturated states of the spin bath (``dark states'') generally have low degrees of polarization and purity, their symmetry properties make them a valuable resource for the coherent manipulation of quantum bits. Specifically, we demonstrate that the dark states of nuclear ensembles can be used to coherently control the system-bath interaction and to provide a robust, long-lived quantum memory for qubit states. 1 aTaylor, J., M.1 aImamoglu, A.1 aLukin, M., D. uhttp://arxiv.org/abs/cond-mat/0308459v101085nas 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/0301323v101322nas a2200169 4500008004100000245007000041210006900111260001400180490000700194520079400201100002300995700002301018700002601041700001901067700002301086856004301109 2003 eng d00aUltracold collision properties of metastable alkaline-earth atoms0 aUltracold collision properties of metastable alkalineearth atoms c2003/2/130 v903 a Ultra-cold collisions of spin-polarized 24Mg,40Ca, and 88Sr in the metastable 3P2 excited state are investigated. We calculate the long-range interaction potentials and estimate the scattering length and the collisional loss rate as a function of magnetic field. The estimates are based on molecular potentials between 3P2 alkaline-earth atoms obtained from ab initio atomic and molecular structure calculations. The scattering lengths show resonance behavior due to the appearance of a molecular bound state in a purely long-range interaction potential and are positive for magnetic fields below 50 mT. A loss-rate model shows that losses should be smallest near zero magnetic field and for fields slightly larger than the resonance field, where the scattering length is also positive. 1 aDerevianko, Andrei1 aPorsev, Sergey, G.1 aKotochigova, Svetlana1 aTiesinga, Eite1 aJulienne, Paul, S. uhttp://arxiv.org/abs/physics/0210076v101384nas a2200181 4500008004100000245004300041210004000084260001500124520088400139100001601023700002001039700002301059700001601082700001901098700001801117700002301135856004401158 2003 eng d00aUltracold Cs$_2$ Feshbach Spectroscopy0 aUltracold Cs2 Feshbach Spectroscopy c2003/12/233 a We have observed and located more than 60 magnetic field-induced Feshbach resonances in ultracold collisions of ground-state $^{133}$Cs atoms. These resonances are associated with molecular states with up to four units of rotational angular momentum, and are detected through variations in the elastic, inelastic, and radiative collision cross sections. These observations allow us to greatly improve upon the interaction potentials between two cesium atoms and to reproduce the positions of most resonances to accuracies better than 0.5%. Based on the relevant coupling scheme between the electron spin, nuclear spin, and orbital angular momenta of the nuclei, quantum numbers and energy structure of the molecular states beneath the dissociation continuum are revealed. Finally, we predict the relevant collision properties for cesium Bose-Einstein condensation experiments. 1 aChin, Cheng1 aVuletic, Vladan1 aKerman, Andrew, J.1 aChu, Steven1 aTiesinga, Eite1 aLeo, Paul, J.1 aWilliams, Carl, J. uhttp://arxiv.org/abs/cond-mat/0312613v201366nas a2200169 4500008004100000245008200041210006900123260001500192490000700207520083000214100002301044700002001067700002201087700002101109700002301130856004301153 2002 eng d00a`Flat Phase' Loading of a Bose-Einstein Condensate into an Optical Lattice 0 aFlat Phase Loading of a BoseEinstein Condensate into an Optical  c2002/11/260 v663 a It has been proposed that the adiabatic loading of a Bose-Einstein Condensate (BEC) into an optical lattice via the Mott-insulator transition can be used to initialize a quantum computer [D. Jaksch, {\it et al.}, Phys. Rev. Lett. {\bf 81}, 3108 (1998)]. The loading of a BEC into the lattice without causing band excitation is readily achievable; however, unless one switches on an optical lattice very slowly, the optical lattice causes a phase to accumulate across the condensate. We show analytically and numerically that a cancellation of this effect is possible by adjusting the harmonic trap force-constant of the magnetic trap appropriately, thereby facilitating quick loading of an optical lattice for quantum computing purposes. A simple analytical theory is developed for a non-stationary BEC in a harmonic trap. 1 aSklarz, Shlomo, E.1 aFriedler, Inbal1 aTannor, David, J.1 aBand, Yehuda, B.1 aWilliams, Carl, J. uhttp://arxiv.org/abs/physics/0209071v1