01467nas a2200193 4500008004100000245005900041210005900100260001400159520089600173100002101069700003001090700001901120700001801139700001601157700002401173700001801197700002101215856003701236 2024 eng d00aPhase transition in magic with random quantum circuits0 aPhase transition in magic with random quantum circuits c4/11/20243 a

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

1 aNiroula, Pradeep1 aWhite, Christopher, David1 aWang, Qingfeng1 aJohri, Sonika1 aZhu, Daiwei1 aMonroe, Christopher1 aNoel, Crystal1 aGullans, Michael uhttps://arxiv.org/abs/2304.1048102266nas a2200265 4500008004100000245005900041210005900100260001400159520150200173100002901675700001801704700002501722700002001747700002501767700001901792700002001811700001201831700001601843700002201859700001301881700002401894700002001918700002501938856003701963 2024 eng d00aSimulating Meson Scattering on Spin Quantum Simulators0 aSimulating Meson Scattering on Spin Quantum Simulators c3/11/20243 a

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

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

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

1 aAlsing, Paul1 aBattle, Phil1 aBienfang, Joshua, C.1 aBorders, Tammie1 aBrower-Thomas, Tina1 aCarr, Lincoln, D.1 aChong, Fred1 aDadras, Siamak1 aDeMarco, Brian1 aDeutsch, Ivan1 aFigueroa, Eden1 aFreedman, Danna1 aEveritt, Henry1 aGauthier, Daniel1 aJohnston-Halperin, Ezekiel1 aKim, Jungsang1 aKira, Mackillo1 aKumar, Prem1 aKwiat, Paul1 aLekki, John1 aLoiacono, Anjul1 aLončar, Marko1 aLowell, John, R.1 aLukin, Mikhail1 aMerzbacher, Celia1 aMiller, Aaron1 aMonroe, Christopher1 aPollanen, Johannes1 aPappas, David1 aRaymer, Michael1 aReano, Ronald1 aRodenburg, Brandon1 aSavage, Martin1 aSearles, Thomas1 aYe, Jun uhttps://arxiv.org/abs/2210.1475701851nas a2200169 4500008004100000245006100041210006000102260001400162520134300176100002501519700001901544700002401563700001801587700001901605700002001624856003701644 2023 eng d00aColloquium: Quantum and Classical Discrete Time Crystals0 aColloquium Quantum and Classical Discrete Time Crystals c5/15/20233 a

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

1 aZaletel, Michael, P.1 aLukin, Mikhail1 aMonroe, Christopher1 aNayak, Chetan1 aWilczek, Frank1 aYao, Norman, Y. uhttps://arxiv.org/abs/2305.0890402080nas a2200193 4500008004100000245009100041210006900132260001500201520147600216100002501692700001301717700001401730700001901744700001601763700002101779700002501800700002401825856003701849 2023 eng d00aObservation of a finite-energy phase transition in a one-dimensional quantum simulator0 aObservation of a finiteenergy phase transition in a onedimension c10/30/20233 a

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

1 aSchuckert, Alexander1 aKatz, Or1 aFeng, Lei1 aCrane, Eleanor1 aDe, Arinjoy1 aHafezi, Mohammad1 aGorshkov, Alexey, V.1 aMonroe, Christopher uhttps://arxiv.org/abs/2310.1986902540nas a2200229 4500008004100000245009600041210006900137260001300206490000700219520184300226100002102069700001802090700001402108700001502122700002802137700002302165700002302188700002402211700001802235700002002253856003702273 2022 eng d00aMany-Body Quantum Teleportation via Operator Spreading in the Traversable Wormhole Protocol0 aManyBody Quantum Teleportation via Operator Spreading in the Tra c8/5/20220 v123 a

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

1 aSchuster, Thomas1 aKobrin, Bryce1 aGao, Ping1 aCong, Iris1 aKhabiboulline, Emil, T.1 aLinke, Norbert, M.1 aLukin, Mikhail, D.1 aMonroe, Christopher1 aYoshida, Beni1 aYao, Norman, Y. uhttps://arxiv.org/abs/2102.0001001181nas a2200145 4500008004100000245008000041210006900121260001300190490000800203520073200211100001300943700001800956700002400974856003700998 2022 eng d00aN-body interactions between trapped ion qubits via spin-dependent squeezing0 aNbody interactions between trapped ion qubits via spindependent  c8/5/20220 v1293 a

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

1 aKatz, Or1 aCetina, Marko1 aMonroe, Christopher uhttps://arxiv.org/abs/2202.0423001894nas a2200301 4500008004100000245006400041210006300105260001400168520102800182100001601210700001701226700001801243700002101261700002201282700001601304700001701320700002201337700003001359700002201389700001901411700002101430700001801451700001801469700002301487700002101510700002401531856003701555 2021 eng d00aCross-Platform Comparison of Arbitrary Quantum Computations0 aCrossPlatform Comparison of Arbitrary Quantum Computations c7/27/20213 a

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

1 aZhu, Daiwei1 aCian, Ze-Pei1 aNoel, Crystal1 aRisinger, Andrew1 aBiswas, Debopriyo1 aEgan, Laird1 aZhu, Yingyue1 aGreen, Alaina, M.1 aAlderete, Cinthia, Huerta1 aNguyen, Nhung, H.1 aWang, Qingfeng1 aMaksymov, Andrii1 aNam, Yunseong1 aCetina, Marko1 aLinke, Norbert, M.1 aHafezi, Mohammad1 aMonroe, Christopher uhttps://arxiv.org/abs/2107.1138702349nas a2200313 4500008004100000245007100041210006900112260001400181520145100195100001601646700003401662700001701696700001801713700001301731700001801744700001901762700002101781700001401802700002201816700001601838700002501854700001801879700001901897700002001916700002001936700001801956700002401974856003701998 2021 eng d00aInteractive Protocols for Classically-Verifiable Quantum Advantage0 aInteractive Protocols for ClassicallyVerifiable Quantum Advantag c12/9/20213 a

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

1 aZhu, Daiwei1 aKahanamoku-Meyer, Gregory, D.1 aLewis, Laura1 aNoel, Crystal1 aKatz, Or1 aHarraz, Bahaa1 aWang, Qingfeng1 aRisinger, Andrew1 aFeng, Lei1 aBiswas, Debopriyo1 aEgan, Laird1 aGheorghiu, Alexandru1 aNam, Yunseong1 aVidick, Thomas1 aVazirani, Umesh1 aYao, Norman, Y.1 aCetina, Marko1 aMonroe, Christopher uhttps://arxiv.org/abs/2112.0515601981nas a2200241 4500008004100000245005400041210005400095260001300149520129500162100002501457700002301482700002001505700002001525700002201545700002201567700001401589700001901603700001801622700001801640700002001658700002401678856003701702 2021 eng d00aObservation of a prethermal discrete time crystal0 aObservation of a prethermal discrete time crystal c2/2/20213 a

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

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

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

1 aNoel, Crystal1 aNiroula, Pradeep1 aZhu, Daiwei1 aRisinger, Andrew1 aEgan, Laird1 aBiswas, Debopriyo1 aCetina, Marko1 aGorshkov, Alexey, V.1 aGullans, Michael1 aHuse, David, A.1 aMonroe, Christopher uhttps://arxiv.org/abs/2106.0588102193nas a2200157 4500008004100000245010400041210006900145260001400214490000600228520169000234100001901924700001301943700002401956700001801980856003701998 2021 eng d00aResource-Optimized Fermionic Local-Hamiltonian Simulation on Quantum Computer for Quantum Chemistry0 aResourceOptimized Fermionic LocalHamiltonian Simulation on Quant c7/21/20210 v53 a

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

1 aWang, Qingfeng1 aLi, Ming1 aMonroe, Christopher1 aNam, Yunseong uhttps://arxiv.org/abs/2004.0415101526nas a2200133 4500008004100000245011300041210006900154260001400223520105400237100002001291700002001311700002401331856003701355 2020 eng d00aThe Character of Motional Modes for Entanglement and Sympathetic Cooling of Mixed-Species Trapped Ion Chains0 aCharacter of Motional Modes for Entanglement and Sympathetic Coo c4/16/20203 a

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

1 aSosnova, Ksenia1 aCarter, Allison1 aMonroe, Christopher uhttps://arxiv.org/abs/2004.0804501563nas a2200169 4500008004100000245002700041210002700068260001400095300001200109490000700121520114400128100002201272700002401294700001801318700002001336856003701356 2020 eng d00aDiscrete Time Crystals0 aDiscrete Time Crystals c3/10/2020 a467-4990 v113 a

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

1 aElse, Dominic, V.1 aMonroe, Christopher1 aNayak, Chetan1 aYao, Norman, Y. uhttps://arxiv.org/abs/1905.1323202128nas a2200229 4500008004100000245006400041210006200105260001400167520146400181100001601645700002301661700001801684700002101702700001601723700002201739700002001761700001501781700002301796700001801819700002401837856003701861 2020 eng d00aFault-Tolerant Operation of a Quantum Error-Correction Code0 aFaultTolerant Operation of a Quantum ErrorCorrection Code c9/24/20203 a

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

1 aEgan, Laird1 aDebroy, Dripto, M.1 aNoel, Crystal1 aRisinger, Andrew1 aZhu, Daiwei1 aBiswas, Debopriyo1 aNewman, Michael1 aLi, Muyuan1 aBrown, Kenneth, R.1 aCetina, Marko1 aMonroe, Christopher uhttps://arxiv.org/abs/2009.1148201522nas 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/2001.0247701551nas a2200193 4500008004100000245009300041210006900134260001300203520092900216100002101145700001901166700002201185700001601207700002401223700002401247700002601271700002301297856003701320 2020 eng d00aQuantum walks and Dirac cellular automata on a programmable trapped-ion quantum computer0 aQuantum walks and Dirac cellular automata on a programmable trap c2/6/20203 a

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

1 aAlderete, Huerta1 aSingh, Shivani1 aNguyen, Nhung, H.1 aZhu, Daiwei1 aBalu, Radhakrishnan1 aMonroe, Christopher1 aChandrashekar, C., M.1 aLinke, Norbert, M. uhttps://arxiv.org/abs/2002.0253701870nas a2200181 4500008004100000245008300041210006900124260001300193490000600206520132100212100002001533700002101553700002401574700001801598700001801616700001701634856003701651 2020 eng d00aTowards analog quantum simulations of lattice gauge theories with trapped ions0 aTowards analog quantum simulations of lattice gauge theories wit c4/8/20200 v23 a

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

1 aDavoudi, Zohreh1 aHafezi, Mohammad1 aMonroe, Christopher1 aPagano, Guido1 aSeif, Alireza1 aShaw, Andrew uhttps://arxiv.org/abs/1908.0321001306nas a2200169 4500008004100000245011300041210006900154260001400223520072000237100001900957700002600976700002401002700002401026700002301050700002601073856003701099 2020 eng d00aUniversal one-dimensional discrete-time quantum walks and their implementation on near term quantum hardware0 aUniversal onedimensional discretetime quantum walks and their im c1/30/20203 a

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

1 aSingh, Shivani1 aAlderete, Cinthia, H.1 aBalu, Radhakrishnan1 aMonroe, Christopher1 aLinke, Norbert, M.1 aChandrashekar, C., M. uhttps://arxiv.org/abs/2001.1119701746nas a2200193 4500008004100000245006800041210006700109260001500176490000900191520117800200100001601378700001801394700001701412700001801429700001901447700002401466700002501490856003701515 2019 eng d00aConfined Dynamics in Long-Range Interacting Quantum Spin Chains0 aConfined Dynamics in LongRange Interacting Quantum Spin Chains c04/17/20190 v122 3 a

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

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

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

1 aAwschalom, David1 aBerggren, Karl, K.1 aBernien, Hannes1 aBhave, Sunil1 aCarr, Lincoln, D.1 aDavids, Paul1 aEconomou, Sophia, E.1 aEnglund, Dirk1 aFaraon, Andrei1 aFejer, Marty1 aGuha, Saikat1 aGustafsson, Martin, V.1 aHu, Evelyn1 aJiang, Liang1 aKim, Jungsang1 aKorzh, Boris1 aKumar, Prem1 aKwiat, Paul, G.1 aLončar, Marko1 aLukin, Mikhail, D.1 aMiller, David, A. B.1 aMonroe, Christopher1 aNam, Sae, Woo1 aNarang, Prineha1 aOrcutt, Jason, S. uhttps://arxiv.org/abs/1912.0664202376nas a2200409 4500008004100000245009100041210006900132260001500201520116700216100001801383700001701401700002201418700002001440700001901460700001901479700002301498700001901521700002101540700001901561700002201580700002001602700002201622700002201644700002101666700002201687700002301709700001901732700002001751700002701771700002201798700001801820700001901838700003001857700002401887700001801911856003701929 2019 eng d00aGround-state energy estimation of the water molecule on a trapped ion quantum computer0 aGroundstate energy estimation of the water molecule on a trapped c03/07/20193 a

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

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

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

1 aQian, Kevin1 aEldredge, Zachary1 aGe, Wenchao1 aPagano, Guido1 aMonroe, Christopher1 aPorto, James, V.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1901.0904201947nas 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/1912.0757701711nas a2200181 4500008004100000245005600041210005600097260001500153490000700168520117600175100002301351700002701374700002101401700001701422700002401439700002901463856003701492 2019 eng d00aQuantum repeaters based on two species trapped ions0 aQuantum repeaters based on two species trapped ions c05/02/20190 v213 a

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

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

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

1 aAltman, Ehud1 aBrown, Kenneth, R.1 aCarleo, Giuseppe1 aCarr, Lincoln, D.1 aDemler, Eugene1 aChin, Cheng1 aDeMarco, Brian1 aEconomou, Sophia, E.1 aEriksson, Mark, A.1 aFu, Kai-Mei, C.1 aGreiner, Markus1 aHazzard, Kaden, R. A.1 aHulet, Randall, G.1 aKollár, Alicia, J.1 aLev, Benjamin, L.1 aLukin, Mikhail, D.1 aMa, Ruichao1 aMi, Xiao1 aMisra, Shashank1 aMonroe, Christopher1 aMurch, Kater1 aNazario, Zaira1 aNi, Kang-Kuen1 aPotter, Andrew, C.1 aRoushan, Pedram uhttps://arxiv.org/abs/1912.0693801552nas a2200169 4500008004100000245007500041210006900116520100400185100001901189700002301208700002201231700002401253700002401277700002001301700002401321856003701345 2018 eng d00aDemonstration of Bayesian quantum game on an ion trap quantum computer0 aDemonstration of Bayesian quantum game on an ion trap quantum co3 a

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

1 aSolmeyer, Neal1 aLinke, Norbert, M.1 aFiggatt, Caroline1 aLandsman, Kevin, A.1 aBalu, Radhakrishnan1 aSiopsis, George1 aMonroe, Christopher uhttps://arxiv.org/abs/1802.0811601264nas a2200157 4500008004100000245006300041210006300104520077600167100002100943700002100964700002000985700002001005700002001025700002401045856003701069 2018 eng d00aHigh Purity Single Photons Entangled with an Atomic Memory0 aHigh Purity Single Photons Entangled with an Atomic Memory3 a

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

1 aCrocker, Clayton1 aLichtman, Martin1 aSosnova, Ksenia1 aCarter, Allison1 aScarano, Sophia1 aMonroe, Christopher uhttps://arxiv.org/abs/1812.0174901532nas a2200193 4500008004100000245009300041210006900134260001500203300001100218490000800229520089100237100002101128700002401149700002201173700002301195700002401218700002301242856007301265 2018 eng d00aRobust two-qubit gates in a linear ion crystal using a frequency-modulated driving force0 aRobust twoqubit gates in a linear ion crystal using a frequencym c2018/01/09 a0205010 v1203 a

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

1 aLeung, Pak, Hong1 aLandsman, Kevin, A.1 aFiggatt, Caroline1 aLinke, Norbert, M.1 aMonroe, Christopher1 aBrown, Kenneth, R. uhttps://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.02050101858nas a2200169 4500008004100000245004400041210004400085520137000129100002401499700002201523700002101545700002301566700001801589700002001607700002401627856003701651 2018 eng d00aVerified Quantum Information Scrambling0 aVerified Quantum Information Scrambling3 a

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

1 aLandsman, Kevin, A.1 aFiggatt, Caroline1 aSchuster, Thomas1 aLinke, Norbert, M.1 aYoshida, Beni1 aYao, Norman, Y.1 aMonroe, Christopher uhttps://arxiv.org/abs/1806.0280702065nas a2200169 4500008004100000245007000041210006900111260001500180520154900195100001601744700001901760700002101779700001801800700001601818700002401834856003701858 2017 eng d00aComplete 3-Qubit Grover Search on a Programmable Quantum Computer0 aComplete 3Qubit Grover Search on a Programmable Quantum Computer c2017/03/303 a

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

1 aFiggatt, C.1 aMaslov, Dmitri1 aLandsman, K., A.1 aLinke, N., M.1 aDebnath, S.1 aMonroe, Christopher uhttps://arxiv.org/abs/1703.1053501709nas a2200229 4500008004100000245006700041210006700108250000700175260001500182300001400197490000800211520106700219100001601286700001901302700002201321700001601343700001601359700002101375700001501396700002401411856004401435 2017 eng d00aExperimental Comparison of Two Quantum Computing Architectures0 aExperimental Comparison of Two Quantum Computing Architectures a13 c2017/03/21 a3305-33100 v1143 a

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

1 aLinke, N.M.1 aMaslov, Dmitri1 aRoetteler, Martin1 aDebnath, S.1 aFiggatt, C.1 aLandsman, K., A.1 aWright, K.1 aMonroe, Christopher uhttp://www.pnas.org/content/114/13/330501522nas a2200133 4500008004100000245007000041210006900111260001500180520109400195100002301289700001601312700002401328856003601352 2016 eng d00aCo-Designing a Scalable Quantum Computer with Trapped Atomic Ions0 aCoDesigning a Scalable Quantum Computer with Trapped Atomic Ions c2016/02/093 aThe first generation of quantum computers are on the horizon, fabricated from quantum hardware platforms that may soon be able to tackle certain tasks that cannot be performed or modelled with conventional computers. These quantum devices will not likely be universal or fully programmable, but special-purpose processors whose hardware will be tightly co-designed with particular target applications. Trapped atomic ions are a leading platform for first generation quantum computers, but are also fundamentally scalable to more powerful general purpose devices in future generations. This is because trapped ion qubits are atomic clock standards that can be made identical to a part in 10^15, and their quantum circuit connectivity can be reconfigured through the use of external fields, without modifying the arrangement or architecture of the qubits themselves. In this article we show how a modular quantum computer of any size can be engineered from ion crystals, and how the wiring between ion trap qubits can be tailored to a variety of applications and quantum computing protocols.1 aBrown, Kenneth, R.1 aKim, Jaewan1 aMonroe, Christopher uhttp://arxiv.org/abs/1602.0284001814nas a2200205 4500008004100000245007600041210006900117260001500186300001100201490000700212520120100219100001901420700002701439700001301466700002301479700002101502700002401523700002501547856003601572 2016 eng d00aKaleidoscope of quantum phases in a long-range interacting spin-1 chain0 aKaleidoscope of quantum phases in a longrange interacting spin1  c2016/05/11 a2051150 v933 aMotivated by recent trapped-ion quantum simulation experiments, we carry out a comprehensive study of the phase diagram of a spin-1 chain with XXZ-type interactions that decay as 1/rα, using a combination of finite and infinite-size DMRG calculations, spin-wave analysis, and field theory. In the absence of long-range interactions, varying the spin-coupling anisotropy leads to four distinct phases: a ferromagnetic Ising phase, a disordered XY phase, a topological Haldane phase, and an antiferromagnetic Ising phase. If long-range interactions are antiferromagnetic and thus frustrated, we find primarily a quantitative change of the phase boundaries. On the other hand, ferromagnetic (non-frustrated) long-range interactions qualitatively impact the entire phase diagram. Importantly, for α≲3, long-range interactions destroy the Haldane phase, break the conformal symmetry of the XY phase, give rise to a new phase that spontaneously breaks a U(1) continuous symmetry, and introduce an exotic tricritical point with no direct parallel in short-range interacting spin chains. We show that the main signatures of all five phases found could be observed experimentally in the near future. 1 aGong, Zhe-Xuan1 aMaghrebi, Mohammad, F.1 aHu, Anzi1 aFoss-Feig, Michael1 aRicherme, Philip1 aMonroe, Christopher1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1510.0210802166nas a2200205 4500008004100000245008500041210006900126260001500195520153900210100001701749700001501766700002101781700002101802700001901823700001901842700001701861700002001878700002401898856003801922 2016 eng d00aMany-body localization in a quantum simulator with programmable random disorder0 aManybody localization in a quantum simulator with programmable r c2016/06/063 a

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

1 aSmith, Jacob1 aLee, Aaron1 aRicherme, Philip1 aNeyenhuis, Brian1 aHess, Paul, W.1 aHauke, Philipp1 aHeyl, Markus1 aHuse, David, A.1 aMonroe, Christopher uhttp://arxiv.org/abs/1508.07026v102028nas a2200229 4500008004100000245008700041210006900128260001300197300001400210490000800224520134100232100002101573700001901594700001501613700001901628700001701647700002301664700002501687700002501712700002401737856003701761 2014 eng d00aNon-local propagation of correlations in long-range interacting quantum systems 0 aNonlocal propagation of correlations in longrange interacting qu c2014/7/9 a198 - 2010 v5113 a The maximum speed with which information can propagate in a quantum many-body system directly affects how quickly disparate parts of the system can become correlated and how difficult the system will be to describe numerically. For systems with only short-range interactions, Lieb and Robinson derived a constant-velocity bound that limits correlations to within a linear effective light cone. However, little is known about the propagation speed in systems with long-range interactions, since the best long-range bound is too loose to give the correct light-cone shape for any known spin model and since analytic solutions rarely exist. In this work, we experimentally determine the spatial and time-dependent correlations of a far-from-equilibrium quantum many-body system evolving under a long-range Ising- or XY-model Hamiltonian. For several different interaction ranges, we extract the shape of the light cone and measure the velocity with which correlations propagate through the system. In many cases we find increasing propagation velocities, which violate the Lieb-Robinson prediction, and in one instance cannot be explained by any existing theory. Our results demonstrate that even modestly-sized quantum simulators are well-poised for studying complicated many-body systems that are intractable to classical computation. 1 aRicherme, Philip1 aGong, Zhe-Xuan1 aLee, Aaron1 aSenko, Crystal1 aSmith, Jacob1 aFoss-Feig, Michael1 aMichalakis, Spyridon1 aGorshkov, Alexey, V.1 aMonroe, Christopher uhttp://arxiv.org/abs/1401.5088v101243nas a2200181 4500008004100000245012700041210006900168260001400237490000700251520064800258100002100906700001900927700001700946700001500963700002200978700002401000856003701024 2013 eng d00aExperimental Performance of a Quantum Simulator: Optimizing Adiabatic Evolution and Identifying Many-Body Ground States 0 aExperimental Performance of a Quantum Simulator Optimizing Adiab c2013/7/310 v883 a We use local adiabatic evolution to experimentally create and determine the ground state spin ordering of a fully-connected Ising model with up to 14 spins. Local adiabatic evolution -- in which the system evolution rate is a function of the instantaneous energy gap -- is found to maximize the ground state probability compared with other adiabatic methods while only requiring knowledge of the lowest $\sim N$ of the $2^N$ Hamiltonian eigenvalues. We also demonstrate that the ground state ordering can be experimentally identified as the most probable of all possible spin configurations, even when the evolution is highly non-adiabatic. 1 aRicherme, Philip1 aSenko, Crystal1 aSmith, Jacob1 aLee, Aaron1 aKorenblit, Simcha1 aMonroe, Christopher uhttp://arxiv.org/abs/1305.2253v101289nas a2200205 4500008004100000245007500041210006900116260001300185490000800198520067800206100002100884700001900905700002200924700001700946700001500963700001900978700002500997700002401022856003701046 2013 eng d00aQuantum Catalysis of Magnetic Phase Transitions in a Quantum Simulator0 aQuantum Catalysis of Magnetic Phase Transitions in a Quantum Sim c2013/9/50 v1113 a We control quantum fluctuations to create the ground state magnetic phases of a classical Ising model with a tunable longitudinal magnetic field using a system of 6 to 10 atomic ion spins. Due to the long-range Ising interactions, the various ground state spin configurations are separated by multiple first-order phase transitions, which in our zero temperature system cannot be driven by thermal fluctuations. We instead use a transverse magnetic field as a quantum catalyst to observe the first steps of the complete fractal devil's staircase, which emerges in the thermodynamic limit and can be mapped to a large number of many-body and energy-optimization problems. 1 aRicherme, Philip1 aSenko, Crystal1 aKorenblit, Simcha1 aSmith, Jacob1 aLee, Aaron1 aIslam, Rajibul1 aCampbell, Wesley, C.1 aMonroe, Christopher uhttp://arxiv.org/abs/1303.6983v201417nas a2200253 4500008004100000245008300041210006900124260001500193300001100208490000700219520068500226100002200911700001600933700002300949700001900972700002300991700001901014700001801033700001701051700001801068700001601086700002401102856003701126 2012 eng d00aQuantum Simulation of Spin Models on an Arbitrary Lattice with Trapped Ions 0 aQuantum Simulation of Spin Models on an Arbitrary Lattice with T c2012/09/27 a0950240 v143 a A collection of trapped atomic ions represents one of the most attractive platforms for the quantum simulation of interacting spin networks and quantum magnetism. Spin-dependent optical dipole forces applied to an ion crystal create long-range effective spin-spin interactions and allow the simulation of spin Hamiltonians that possess nontrivial phases and dynamics. Here we show how appropriate design of laser fields can provide for arbitrary multidimensional spin-spin interaction graphs even for the case of a linear spatial array of ions. This scheme uses currently existing trap technology and is scalable to levels where classical methods of simulation are intractable. 1 aKorenblit, Simcha1 aKafri, Dvir1 aCampbell, Wess, C.1 aIslam, Rajibul1 aEdwards, Emily, E.1 aGong, Zhe-Xuan1 aLin, Guin-Dar1 aDuan, Luming1 aKim, Jungsang1 aKim, Kihwan1 aMonroe, Christopher uhttp://arxiv.org/abs/1201.0776v102052nas a2200193 4500008004100000245002200041210002200063260001300085300001200098490000800110520156800118100002301686700001901709700002201728700002301750700002401773700002401797856003701821 2010 eng d00aQuantum Computing0 aQuantum Computing c2010/3/4 a45 - 530 v4643 a Quantum mechanics---the theory describing the fundamental workings of nature---is famously counterintuitive: it predicts that a particle can be in two places at the same time, and that two remote particles can be inextricably and instantaneously linked. These predictions have been the topic of intense metaphysical debate ever since the theory's inception early last century. However, supreme predictive power combined with direct experimental observation of some of these unusual phenomena leave little doubt as to its fundamental correctness. In fact, without quantum mechanics we could not explain the workings of a laser, nor indeed how a fridge magnet operates. Over the last several decades quantum information science has emerged to seek answers to the question: can we gain some advantage by storing, transmitting and processing information encoded in systems that exhibit these unique quantum properties? Today it is understood that the answer is yes. Many research groups around the world are working towards one of the most ambitious goals humankind has ever embarked upon: a quantum computer that promises to exponentially improve computational power for particular tasks. A number of physical systems, spanning much of modern physics, are being developed for this task---ranging from single particles of light to superconducting circuits---and it is not yet clear which, if any, will ultimately prove successful. Here we describe the latest developments for each of the leading approaches and explain what the major challenges are for the future. 1 aLadd, Thaddeus, D.1 aJelezko, Fedor1 aLaflamme, Raymond1 aNakamura, Yasunobu1 aMonroe, Christopher1 aO'Brien, Jeremy, L. uhttp://arxiv.org/abs/1009.2267v101474nas a2200133 4500008004100000245009500041210006900136260001500205490000700220520103800227100001401265700002401279856003701303 2009 eng d00aProtocol for Hybrid Entanglement Between a Trapped Atom and a Semiconductor Quantum Dot 0 aProtocol for Hybrid Entanglement Between a Trapped Atom and a Se c2009/12/300 v803 a We propose a quantum optical interface between an atomic and solid state system. We show that quantum states in a single trapped atom can be entangled with the states of a semiconductor quantum dot through their common interaction with a classical laser field. The interference and detection of the resulting scattered photons can then herald the entanglement of the disparate atomic and solid-state quantum bits. We develop a protocol that can succeed despite a significant mismatch in the radiative characteristics of the two matter-based qubits. We study in detail a particular case of this interface applied to a single trapped \Yb ion and a cavity-coupled InGaAs semiconductor quantum dot. Entanglement fidelity and success rates are found to be robust to a broad range of experimental nonideal effects such as dispersion mismatch, atom recoil, and multi-photon scattering. We conclude that it should be possible to produce highly entangled states of these complementary qubit systems under realistic experimental conditions. 1 aWaks, Edo1 aMonroe, Christopher uhttp://arxiv.org/abs/0907.0444v1