01851nas 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/2305.0890401726nas a2200253 4500008004100000022001400041245005000055210005000105260001500155490000600170520104100176100002201217700002201239700001801261700002101279700001601300700001301316700002901329700001801358700002401376700001901400700001601419856003701435 2023 eng d a2375-254800aDigital quantum simulation of NMR experiments0 aDigital quantum simulation of NMR experiments c11/29/20230 v93 aSimulations of nuclear magnetic resonance (NMR) experiments can be an important tool for extracting information about molecular structure and optimizing experimental protocols but are often intractable on classical computers for large molecules such as proteins and for protocols such as zero-field NMR. We demonstrate the first quantum simulation of an NMR spectrum, computing the zero-field spectrum of the methyl group of acetonitrile using four qubits of a trapped-ion quantum computer. We reduce the sampling cost of the quantum simulation by an order of magnitude using compressed sensing techniques. We show how the intrinsic decoherence of NMR systems may enable the zero-field simulation of classically hard molecules on relatively near-term quantum hardware and discuss how the experimentally demonstrated quantum algorithm can be used to efficiently simulate scientifically and technologically relevant solid-state NMR experiments on more mature devices. Our work opens a practical application for quantum computation.
1 aSeetharam, Kushal1 aBiswas, Debopriyo1 aNoel, Crystal1 aRisinger, Andrew1 aZhu, Daiwei1 aKatz, Or1 aChattopadhyay, Sambuddha1 aCetina, Marko1 aMonroe, Christopher1 aDemler, Eugene1 aSels, Dries uhttps://arxiv.org/abs/2109.1329801306nas a2200133 4500008004100000245005800041210005800099260001300157520089200170100002101062700002701083700002501110856003701135 2023 eng d00aError Mitigation Thresholds in Noisy Quantum Circuits0 aError Mitigation Thresholds in Noisy Quantum Circuits c2/8/20233 aExtracting useful information from noisy near-term quantum simulations requires error mitigation strategies. A broad class of these strategies rely on precise characterization of the noise source. We study the performance of such strategies when the noise is imperfectly characterized. We adapt an Imry-Ma argument to predict the existence of an error mitigation threshold for random spatially local circuits in spatial dimensions D≥2: characterization disorder below the threshold rate allows for error mitigation up to times that scale with the number of qubits. For one-dimensional circuits, by contrast, mitigation fails at an O(1) time for any imperfection in the characterization of disorder. We discuss implications for tests of quantum computational advantage, fault-tolerant probes of measurement-induced phase transitions, and quantum algorithms in near-term devices.
1 aNiroula, Pradeep1 aGopalakrishnan, Sarang1 aGullans, Michael, J. uhttps://arxiv.org/abs/2302.0427801229nas a2200157 4500008004100000245007900041210006900120260001300189520074400202100001900946700001700965700001300982700002100995700001801016856003701034 2023 eng d00aEver more optimized simulations of fermionic systems on a quantum computer0 aEver more optimized simulations of fermionic systems on a quantu c3/6/20233 aDespite using a novel model of computation, quantum computers break down programs into elementary gates. Among such gates, entangling gates are the most expensive. In the context of fermionic simulations, we develop a suite of compilation and optimization techniques that massively reduce the entangling-gate counts. We exploit the well-studied non-quantum optimization algorithms to achieve up to 24\% savings over the state of the art for several small-molecule simulations, with no loss of accuracy or hidden costs. Our methodologies straightforwardly generalize to wider classes of near-term simulations of the ground state of a fermionic system or real-time simulations probing dynamical properties of a fermionic system.
1 aWang, Qingfeng1 aCian, Ze-Pei1 aLi, Ming1 aMarkov, Igor, L.1 aNam, Yunseong uhttps://arxiv.org/abs/2303.0346001864nas a2200145 4500008004100000245007100041210006900112260001500181520139900196100001601595700002101611700002401632700002501656856003701681 2023 eng d00aFault-Tolerant Quantum Memory using Low-Depth Random Circuit Codes0 aFaultTolerant Quantum Memory using LowDepth Random Circuit Codes c11/29/20233 aLow-depth random circuit codes possess many desirable properties for quantum error correction but have so far only been analyzed in the code capacity setting where it is assumed that encoding gates and syndrome measurements are noiseless. In this work, we design a fault-tolerant distillation protocol for preparing encoded states of one-dimensional random circuit codes even when all gates and measurements are subject to noise. This is sufficient for fault-tolerant quantum memory since these encoded states can then be used as ancillas for Steane error correction. We show through numerical simulations that our protocol can correct erasure errors up to an error rate of 2%. In addition, we also extend results in the code capacity setting by developing a maximum likelihood decoder for depolarizing noise similar to work by Darmawan et al. As in their work, we formulate the decoding problem as a tensor network contraction and show how to contract the network efficiently by exploiting the low-depth structure. Replacing the tensor network with a so-called ''tropical'' tensor network, we also show how to perform minimum weight decoding. With these decoders, we are able to numerically estimate the depolarizing error threshold of finite-rate random circuit codes and show that this threshold closely matches the hashing bound even when the decoding is sub-optimal.
1 aNelson, Jon1 aBentsen, Gregory1 aFlammia, Steven, T.1 aGullans, Michael, J. uhttps://arxiv.org/abs/2311.1798501577nas a2200145 4500008004100000245006900041210006300110260001400173520112200187100002101309700002101330700001601351700002701367856003701394 2023 eng d00aHamiltonians whose low-energy states require $\Omega(n)$ T gates0 aHamiltonians whose lowenergy states require Omegan T gates c10/2/20233 aThe recent resolution of the NLTS Conjecture [ABN22] establishes a prerequisite to the Quantum PCP (QPCP) Conjecture through a novel use of newly-constructed QLDPC codes [LZ22]. Even with NLTS now solved, there remain many independent and unresolved prerequisites to the QPCP Conjecture, such as the NLSS Conjecture of [GL22]. In this work we focus on a specific and natural prerequisite to both NLSS and the QPCP Conjecture, namely, the existence of local Hamiltonians whose low-energy states all require ω(logn) T gates to prepare. In fact, we prove a stronger result which is not necessarily implied by either conjecture: we construct local Hamiltonians whose low-energy states require Ω(n) T gates. Following a previous work [CCNN23], we further show that our procedure can be applied to the NLTS Hamiltonians of [ABN22] to yield local Hamiltonians whose low-energy states require both Ω(logn)-depth and Ω(n) T gates to prepare. Our results utilize a connection between T-count and stabilizer groups, which was recently applied in the context of learning low T-count states [GIKL23a, GIKL23b, GIKL23c].
1 aCoble, Nolan, J.1 aCoudron, Matthew1 aNelson, Jon1 aNezhadi, Seyed, Sajjad uhttps://arxiv.org/abs/2310.0134701454nas a2200145 4500008004100000245006000041210005900101260001400160520101200174100002101186700002101207700001601228700002701244856003701271 2023 eng d00aLocal Hamiltonians with no low-energy stabilizer states0 aLocal Hamiltonians with no lowenergy stabilizer states c2/28/20233 aThe recently-defined No Low-energy Sampleable States (NLSS) conjecture of Gharibian and Le Gall [GL22] posits the existence of a family of local Hamiltonians where all states of low-enough constant energy do not have succinct representations allowing perfect sampling access. States that can be prepared using only Clifford gates (i.e. stabilizer states) are an example of sampleable states, so the NLSS conjecture implies the existence of local Hamiltonians whose low-energy space contains no stabilizer states. We describe families that exhibit this requisite property via a simple alteration to local Hamiltonians corresponding to CSS codes. Our method can also be applied to the recent NLTS Hamiltonians of Anshu, Breuckmann, and Nirkhe [ABN22], resulting in a family of local Hamiltonians whose low-energy space contains neither stabilizer states nor trivial states. We hope that our techniques will eventually be helpful for constructing Hamiltonians which simultaneously satisfy NLSS and NLTS.
1 aCoble, Nolan, J.1 aCoudron, Matthew1 aNelson, Jon1 aNezhadi, Seyed, Sajjad uhttps://arxiv.org/abs/2302.1475501354nas a2200157 4500008004100000245006100041210005900102260001400161520088700175100002301062700001601085700002301101700002001124700001501144856003701159 2023 eng d00aA quantum central path algorithm for linear optimization0 aquantum central path algorithm for linear optimization c11/7/20233 aWe 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/2311.0397701594nas a2200217 4500008004100000245004000041210004000081260001400121520100000135100002101135700001601156700001501172700002201187700002001209700001901229700001901248700002501267700002201292700002501314856003701339 2023 eng d00aQuantum Sensing with Erasure Qubits0 aQuantum Sensing with Erasure Qubits c10/2/20233 aThe 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, Michael, J.1 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 aComputational 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/2312.0973301745nas a2200181 4500008004100000245006600041210006300107260001300170520118700183100001801370700002301388700002401411700002101435700002001456700002501476700002501501856003701526 2023 eng d00aA sharp phase transition in linear cross-entropy benchmarking0 asharp phase transition in linear crossentropy benchmarking c5/8/20233 aDemonstrations of quantum computational advantage and benchmarks of quantum processors via quantum random circuit sampling are based on evaluating the linear cross-entropy benchmark (XEB). A key question in the theory of XEB is whether it approximates the fidelity of the quantum state preparation. Previous works have shown that the XEB generically approximates the fidelity in a regime where the noise rate per qudit ε satisfies εN≪1 for a system of N qudits and that this approximation breaks down at large noise rates. Here, we show that the breakdown of XEB as a fidelity proxy occurs as a sharp phase transition at a critical value of εN that depends on the circuit architecture and properties of the two-qubit gates, including in particular their entangling power. We study the phase transition using a mapping of average two-copy quantities to statistical mechanics models in random quantum circuit architectures with full or one-dimensional connectivity. We explain the phase transition behavior in terms of spectral properties of the transfer matrix of the statistical mechanics model and identify two-qubit gate sets that exhibit the largest noise robustness.
1 aWare, Brayden1 aDeshpande, Abhinav1 aHangleiter, Dominik1 aNiroula, Pradeep1 aFefferman, Bill1 aGorshkov, Alexey, V.1 aGullans, Michael, J. uhttps://arxiv.org/abs/2305.0495401473nas a2200133 4500008004100000245007900041210006900120260001500189520102500204100002101229700002701250700002501277856003701302 2023 eng d00aThresholds in the Robustness of Error Mitigation in Noisy Quantum Dynamics0 aThresholds in the Robustness of Error Mitigation in Noisy Quantu c10/30/20233 aExtracting useful information from noisy near-term quantum simulations requires error mitigation strategies. A broad class of these strategies rely on precise characterization of the noise source. We study the robustness of such strategies when the noise is imperfectly characterized. We adapt an Imry-Ma argument to predict the existence of a threshold in the robustness of error mitigation for random spatially local circuits in spatial dimensions D≥2: noise characterization disorder below the threshold rate allows for error mitigation up to times that scale with the number of qubits. For one-dimensional circuits, by contrast, mitigation fails at an O(1) time for any imperfection in the characterization of disorder. As a result, error mitigation is only a practical method for sufficiently well-characterized noise. We discuss further implications for tests of quantum computational advantage, fault-tolerant probes of measurement-induced phase transitions, and quantum algorithms in near-term devices.
1 aNiroula, Pradeep1 aGopalakrishnan, Sarang1 aGullans, Michael, J. uhttps://arxiv.org/abs/2302.0427801498nas a2200301 4500008004100000245006800041210006800109260001400177520060600191653002700797653004400824653003100868100001700899700001600916700002500932700001800957700001300975700001800988700001901006700002101025700001401046700002201060700001601082700001901098700001801117700002401135856003701159 2022 eng d00aExperimental Implementation of an Efficient Test of Quantumness0 aExperimental Implementation of an Efficient Test of Quantumness c9/28/20223 aA test of quantumness is a protocol where a classical user issues challenges to a quantum device to determine if it exhibits non-classical behavior, under certain cryptographic assumptions. Recent attempts to implement such tests on current quantum computers rely on either interactive challenges with efficient verification, or non-interactive challenges with inefficient (exponential time) verification. In this paper, we execute an efficient non-interactive test of quantumness on an ion-trap quantum computer. Our results significantly exceed the bound for a classical device's success.
10aFOS: Physical sciences10aOther Condensed Matter (cond-mat.other)10aQuantum Physics (quant-ph)1 aLewis, Laura1 aZhu, Daiwei1 aGheorghiu, Alexandru1 aNoel, Crystal1 aKatz, Or1 aHarraz, Bahaa1 aWang, Qingfeng1 aRisinger, Andrew1 aFeng, Lei1 aBiswas, Debopriyo1 aEgan, Laird1 aVidick, Thomas1 aCetina, Marko1 aMonroe, Christopher uhttps://arxiv.org/abs/2209.1431601849nas a2200181 4500008004100000245006500041210006400106260001400170520120700184653004101391653005301432653005401485653002701539100002001566700002201586700002201608856003701630 2022 eng d00aMachine-assisted discovery of integrable symplectic mappings0 aMachineassisted discovery of integrable symplectic mappings c3/22/20223 aWe present a new automated method for finding integrable symplectic maps of the plane. These dynamical systems possess a hidden symmetry associated with an existence of conserved quantities, i.e. integrals of motion. The core idea of the algorithm is based on the knowledge that the evolution of an integrable system in the phase space is restricted to a lower-dimensional submanifold. Limiting ourselves to polygon invariants of motion, we analyze the shape of individual trajectories thus successfully distinguishing integrable motion from chaotic cases. For example, our method rediscovers some of the famous McMillan-Suris integrable mappings and discrete Painlevé equations. In total, over 100 new integrable families are presented and analyzed; some of them are isolated in the space of parameters, and some of them are families with one parameter (or the ratio of parameters) being continuous or discrete. At the end of the paper, we suggest how newly discovered maps are related to a general 2D symplectic map via an introduction of discrete perturbation theory and propose a method on how to construct smooth near-integrable dynamical systems based on mappings with polygon invariants.
10aAccelerator Physics (physics.acc-ph)10aAdaptation and Self-Organizing Systems (nlin.AO)10aExactly Solvable and Integrable Systems (nlin.SI)10aFOS: Physical sciences1 aZolkin, Timofey1 aKharkov, Yaroslav1 aNagaitsev, Sergei uhttps://arxiv.org/abs/2201.1313302845nas a2200541 4500008004100000245004700041210004700088260001300135520125300148653002701401653004401428653004901472653004201521653002901563653003101592100002501623700002001648700002101668700002501689700002001714700002201734700002001756700002001776700001801796700002101814700002101835700001601856700001801872700001501890700001901905700002101924700002401945700002201969700001801991700001902009700002002028700002402048700002402072700002302096700001902119700002002138700002202158700001802180700002102198700002602219700002102245856003702266 2022 eng d00aQuantum Simulation for High Energy Physics0 aQuantum Simulation for High Energy Physics c4/7/20223 aIt is for the first time that Quantum Simulation for High Energy Physics (HEP) is studied in the U.S. decadal particle-physics community planning, and in fact until recently, this was not considered a mainstream topic in the community. This fact speaks of a remarkable rate of growth of this subfield over the past few years, stimulated by the impressive advancements in Quantum Information Sciences (QIS) and associated technologies over the past decade, and the significant investment in this area by the government and private sectors in the U.S. and other countries. High-energy physicists have quickly identified problems of importance to our understanding of nature at the most fundamental level, from tiniest distances to cosmological extents, that are intractable with classical computers but may benefit from quantum advantage. They have initiated, and continue to carry out, a vigorous program in theory, algorithm, and hardware co-design for simulations of relevance to the HEP mission. This community whitepaper is an attempt to bring this exciting and yet challenging area of research to the spotlight, and to elaborate on what the promises, requirements, challenges, and potential solutions are over the next decade and beyond.
10aFOS: Physical sciences10aHigh Energy Physics - Lattice (hep-lat)10aHigh Energy Physics - Phenomenology (hep-ph)10aHigh Energy Physics - Theory (hep-th)10aNuclear Theory (nucl-th)10aQuantum Physics (quant-ph)1 aBauer, Christian, W.1 aDavoudi, Zohreh1 aBalantekin, Baha1 aBhattacharya, Tanmoy1 aCarena, Marcela1 ade Jong, Wibe, A.1 aDraper, Patrick1 aEl-Khadra, Aida1 aGemelke, Nate1 aHanada, Masanori1 aKharzeev, Dmitri1 aLamm, Henry1 aLi, Ying-Ying1 aLiu, Junyu1 aLukin, Mikhail1 aMeurice, Yannick1 aMonroe, Christopher1 aNachman, Benjamin1 aPagano, Guido1 aPreskill, John1 aRinaldi, Enrico1 aRoggero, Alessandro1 aSantiago, David, I.1 aSavage, Martin, J.1 aSiddiqi, Irfan1 aSiopsis, George1 aVan Zanten, David1 aWiebe, Nathan1 aYamauchi, Yukari1 aYeter-Aydeniz, Kübra1 aZorzetti, Silvia uhttps://arxiv.org/abs/2204.0338102255nas a2200205 4500008004100000245005300041210005000094260001300144520167300157100002001830700002001850700002301870700002101893700001601914700002401930700002501954700001701979700001601996856003702012 2022 eng d00aA single T-gate makes distribution learning hard0 asingle Tgate makes distribution learning hard c7/7/20223 aThe task of learning a probability distribution from samples is ubiquitous across the natural sciences. The output distributions of local quantum circuits form a particularly interesting class of distributions, of key importance both to quantum advantage proposals and a variety of quantum machine learning algorithms. In this work, we provide an extensive characterization of the learnability of the output distributions of local quantum circuits. Our first result yields insight into the relationship between the efficient learnability and the efficient simulatability of these distributions. Specifically, we prove that the density modelling problem associated with Clifford circuits can be efficiently solved, while for depth d=nΩ(1) circuits the injection of a single T-gate into the circuit renders this problem hard. This result shows that efficient simulatability does not imply efficient learnability. Our second set of results provides insight into the potential and limitations of quantum generative modelling algorithms. We first show that the generative modelling problem associated with depth d=nΩ(1) local quantum circuits is hard for any learning algorithm, classical or quantum. As a consequence, one cannot use a quantum algorithm to gain a practical advantage for this task. We then show that, for a wide variety of the most practically relevant learning algorithms -- including hybrid-quantum classical algorithms -- even the generative modelling problem associated with depth d=ω(log(n)) Clifford circuits is hard. This result places limitations on the applicability of near-term hybrid quantum-classical generative modelling algorithms.
1 aHinsche, Marcel1 aIoannou, Marios1 aNietner, Alexander1 aHaferkamp, Jonas1 aQuek, Yihui1 aHangleiter, Dominik1 aSeifert, Jean-Pierre1 aEisert, Jens1 aSweke, Ryan uhttps://arxiv.org/abs/2207.0314001811nas a2200205 4500008004100000245005900041210005900100260001300159490000600172520120100178653002701379653003501406653003101441100001601472700002101488700001501509700001901524700002501543856003701568 2022 eng d00aUniversal scattering with general dispersion relations0 aUniversal scattering with general dispersion relations c4/6/20220 v43 aMany synthetic quantum systems allow particles to have dispersion relations that are neither linear nor quadratic functions. Here, we explore single-particle scattering in general spatial dimension D≥1 when the density of states diverges at a specific energy. To illustrate the underlying principles in an experimentally relevant setting, we focus on waveguide quantum electrodynamics (QED) problems (i.e. D=1) with dispersion relation ϵ(k)=±|d|km, where m≥2 is an integer. For a large class of these problems for any positive integer m, we rigorously prove that when there are no bright zero-energy eigenstates, the S-matrix evaluated at an energy E→0 converges to a universal limit that is only dependent on m. We also give a generalization of a key index theorem in quantum scattering theory known as Levinson's theorem -- which relates the scattering phases to the number of bound states -- to waveguide QED scattering for these more general dispersion relations. We then extend these results to general integer dimensions D≥1, dispersion relations ϵ(k)=|k|a for a D-dimensional momentum vector k with any real positive a, and separable potential scattering.
10aFOS: Physical sciences10aMathematical Physics (math-ph)10aQuantum Physics (quant-ph)1 aWang, Yidan1 aGullans, Michael1 aNa, Xuesen1 aWhitsitt, Seth1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2103.0983001418nas a2200157 4500008004100000245008100041210006900122260001400191490000600205520093500211100001601146700002101162700001501183700002501198856003701223 2022 eng d00aUniversality in one-dimensional scattering with general dispersion relations0 aUniversality in onedimensional scattering with general dispersio c3/17/20210 v43 aMany synthetic quantum systems allow particles to have dispersion relations that are neither linear nor quadratic functions. Here, we explore single-particle scattering in one dimension when the dispersion relation is ϵ(k)=±|d|km, where m≥2 is an integer. We study impurity scattering problems in which a single-particle in a one-dimensional waveguide scatters off of an inhomogeneous, discrete set of sites locally coupled to the waveguide. For a large class of these problems, we rigorously prove that when there are no bright zero-energy eigenstates, the S-matrix evaluated at an energy E→0 converges to a universal limit that is only dependent on m. We also give a generalization of a key index theorem in quantum scattering theory known as Levinson's theorem -- which relates the scattering phases to the number of bound states -- to impurity scattering for these more general dispersion relations.
1 aWang, Yidan1 aGullans, Michael1 aNa, Xuesen1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2103.0983001979nas 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 aPhotocurrent (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/2110.0107901894nas a2200301 4500008004100000245006400041210006300105260001400168520102800182100001601210700001701226700001801243700002101261700002201282700001601304700001701320700002201337700003001359700002201389700001901411700002101430700001801451700001801469700002301487700002101510700002401531856003701555 2021 eng d00aCross-Platform Comparison of Arbitrary Quantum Computations0 aCrossPlatform Comparison of Arbitrary Quantum Computations c7/27/20213 aAs 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/2107.1138702078nas a2200277 4500008004100000245006700041210006600108260001500174520125200189100002201441700001801463700002501481700002101506700002401527700002501551700002101576700002001597700002501617700002601642700001601668700001901684700002301703700001801726700001901744856003701763 2021 eng d00aDevice-independent Randomness Expansion with Entangled Photons0 aDeviceindependent Randomness Expansion with Entangled Photons c01/28/20213 aWith the growing availability of experimental loophole-free Bell tests, it has become possible to implement a new class of device-independent random number generators whose output can be certified to be uniformly random without requiring a detailed model of the quantum devices used. However, all of these experiments require many input bits in order to certify a small number of output bits, and it is an outstanding challenge to develop a system that generates more randomness than is used. Here, we devise a device-independent spot-checking protocol which uses only uniform bits as input. Implemented with a photonic loophole-free Bell test, we can produce 24% more certified output bits (1,181,264,237) than consumed input bits (953,301,640), which is 5 orders of magnitude more efficient than our previous work [arXiv:1812.07786]. The experiment ran for 91.0 hours, creating randomness at an average rate of 3606 bits/s with a soundness error bounded by 5.7×10−7 in the presence of classical side information. Our system will allow for greater trust in public sources of randomness, such as randomness beacons, and the protocols may one day enable high-quality sources of private randomness as the device footprint shrinks.
1 aShalm, Lynden, K.1 aZhang, Yanbao1 aBienfang, Joshua, C.1 aSchlager, Collin1 aStevens, Martin, J.1 aMazurek, Michael, D.1 aAbellán, Carlos1 aAmaya, Waldimar1 aMitchell, Morgan, W.1 aAlhejji, Mohammad, A.1 aFu, Honghao1 aOrnstein, Joel1 aMirin, Richard, P.1 aNam, Sae, Woo1 aKnill, Emanuel uhttps://arxiv.org/abs/1912.1115801622nas a2200145 4500008004100000245008500041210006900126260001400195520114800209100002201357700002101379700002101400700001801421856003701439 2021 eng d00aEfficient quantum programming using EASE gates on a trapped-ion quantum computer0 aEfficient quantum programming using EASE gates on a trappedion q c7/15/20213 aParallel operations in conventional computing have proven to be an essential tool for efficient and practical computation, and the story is not different for quantum computing. Indeed, there exists a large body of works that study advantages of parallel implementations of quantum gates for efficient quantum circuit implementations. Here, we focus on the recently invented efficient, arbitrary, simultaneously entangling (EASE) gates, available on a trapped-ion quantum computer. Leveraging its flexibility in selecting arbitrary pairs of qubits to be coupled with any degrees of entanglement, all in parallel, we show a n-qubit Clifford circuit can be implemented using 6log(n) EASE gates, a n-qubit multiply-controlled NOT gate can be implemented using 3n/2 EASE gates, and a n-qubit permutation can be implemented using six EASE gates. We discuss their implications to near-term quantum chemistry simulations and the state of the art pattern matching algorithm. Given Clifford + multiply-controlled NOT gates form a universal gate set for quantum computing, our results imply efficient quantum computation by EASE gates, in general.
1 aGrzesiak, Nikodem1 aMaksymov, Andrii1 aNiroula, Pradeep1 aNam, Yunseong uhttps://arxiv.org/abs/2107.0759101588nas a2200241 4500008004100000022001400041245008300055210006900138260001400207300001100221490000600232520086600238100002401104700002201128700002101150700001801171700002801189700001401217700002401231700002301255700002101278856004701299 2021 eng d a2058-956500aEntangled quantum cellular automata, physical complexity, and Goldilocks rules0 aEntangled quantum cellular automata physical complexity and Gold c9/29/2021 a0450170 v63 aCellular automata are interacting classical bits that display diverse emergent behaviors, from fractals to random-number generators to Turing-complete computation. We discover that quantum cellular automata (QCA) can exhibit complexity in the sense of the complexity science that describes biology, sociology, and economics. QCA exhibit complexity when evolving under "Goldilocks rules" that we define by balancing activity and stasis. Our Goldilocks rules generate robust dynamical features (entangled breathers), network structure and dynamics consistent with complexity, and persistent entropy fluctuations. Present-day experimental platforms -- Rydberg arrays, trapped ions, and superconducting qubits -- can implement our Goldilocks protocols, making testable the link between complexity science and quantum computation exposed by our QCA.
1 aHillberry, Logan, E1 aJones, Matthew, T1 aVargas, David, L1 aRall, Patrick1 aHalpern, Nicole, Yunger1 aBao, Ning1 aNotarnicola, Simone1 aMontangero, Simone1 aCarr, Lincoln, D uhttp://dx.doi.org/10.1088/2058-9565/ac1c4102349nas a2200313 4500008004100000245007100041210006900112260001400181520145100195100001601646700003401662700001701696700001801713700001301731700001801744700001901762700002101781700001401802700002201816700001601838700002501854700001801879700001901897700002001916700002001936700001801956700002401974856003701998 2021 eng d00aInteractive Protocols for Classically-Verifiable Quantum Advantage0 aInteractive Protocols for ClassicallyVerifiable Quantum Advantag c12/9/20213 aAchieving 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/2112.0515602430nas a2200205 4500008004100000245007100041210006900112260001500181520180900196100002002005700002002025700002302045700002102068700001602089700002402105700002502129700001702154700001602171856003702187 2021 eng d00aLearnability of the output distributions of local quantum circuits0 aLearnability of the output distributions of local quantum circui c10/11/20213 aThere is currently a large interest in understanding the potential advantages quantum devices can offer for probabilistic modelling. In this work we investigate, within two different oracle models, the probably approximately correct (PAC) learnability of quantum circuit Born machines, i.e., the output distributions of local quantum circuits. We first show a negative result, namely, that the output distributions of super-logarithmic depth Clifford circuits are not sample-efficiently learnable in the statistical query model, i.e., when given query access to empirical expectation values of bounded functions over the sample space. This immediately implies the hardness, for both quantum and classical algorithms, of learning from statistical queries the output distributions of local quantum circuits using any gate set which includes the Clifford group. As many practical generative modelling algorithms use statistical queries -- including those for training quantum circuit Born machines -- our result is broadly applicable and strongly limits the possibility of a meaningful quantum advantage for learning the output distributions of local quantum circuits. As a positive result, we show that in a more powerful oracle model, namely when directly given access to samples, the output distributions of local Clifford circuits are computationally efficiently PAC learnable by a classical learner. Our results are equally applicable to the problems of learning an algorithm for generating samples from the target distribution (generative modelling) and learning an algorithm for evaluating its probabilities (density modelling). They provide the first rigorous insights into the learnability of output distributions of local quantum circuits from the probabilistic modelling perspective.
1 aHinsche, Marcel1 aIoannou, Marios1 aNietner, Alexander1 aHaferkamp, Jonas1 aQuek, Yihui1 aHangleiter, Dominik1 aSeifert, Jean-Pierre1 aEisert, Jens1 aSweke, Ryan uhttps://arxiv.org/abs/2110.0551702079nas a2200133 4500008004100000245007300041210006900114260001400183520164800197100002001845700002701865700001601892856003701908 2021 eng d00aNonlocal Games, Compression Theorems, and the Arithmetical Hierarchy0 aNonlocal Games Compression Theorems and the Arithmetical Hierarc c10/9/20213 aWe investigate the connection between the complexity of nonlocal games and the arithmetical hierarchy, a classification of languages according to the complexity of arithmetical formulas defining them. It was recently shown by Ji, Natarajan, Vidick, Wright and Yuen that deciding whether the (finite-dimensional) quantum value of a nonlocal game is 1 or at most 12 is complete for the class Σ1 (i.e., RE). A result of Slofstra implies that deciding whether the commuting operator value of a nonlocal game is equal to 1 is complete for the class Π1 (i.e., coRE). We prove that deciding whether the quantum value of a two-player nonlocal game is exactly equal to 1 is complete for Π2; this class is in the second level of the arithmetical hierarchy and corresponds to formulas of the form "∀x∃yϕ(x,y)". This shows that exactly computing the quantum value is strictly harder than approximating it, and also strictly harder than computing the commuting operator value (either exactly or approximately). We explain how results about the complexity of nonlocal games all follow in a unified manner from a technique known as compression. At the core of our Π2-completeness result is a new "gapless" compression theorem that holds for both quantum and commuting operator strategies. Our compression theorem yields as a byproduct an alternative proof of Slofstra's result that the set of quantum correlations is not closed. We also show how a "gap-preserving" compression theorem for commuting operator strategies would imply that approximating the commuting operator value is complete for Π1.
1 aMousavi, Hamoon1 aNezhadi, Seyed, Sajjad1 aYuen, Henry uhttps://arxiv.org/abs/2110.0465101981nas a2200241 4500008004100000245005400041210005400095260001300149520129500162100002501457700002301482700002001505700002001525700002201545700002201567700001401589700001901603700001801622700001801640700002001658700002401678856003701702 2021 eng d00aObservation of a prethermal discrete time crystal0 aObservation of a prethermal discrete time crystal c2/2/20213 aThe 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 aMany-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/2106.0588101481nas a2200193 4500008004100000245004300041210004200084260001400126300001100140490000800151520095100159100001501110700002001125700002301145700001801168700002001186700001701206856006401223 2021 eng d00aPhase-engineered bosonic quantum codes0 aPhaseengineered bosonic quantum codes c6/29/2021 a0624270 v1033 aContinuous-variable systems protected by bosonic quantum codes have emerged as a promising platform for quantum information. To date, the design of code words has centered on optimizing the state occupation in the relevant basis to generate the distance needed for error correction. Here, we show tuning the phase degree of freedom in the design of code words can affect, and potentially enhance, the protection against Markovian errors that involve excitation exchange with the environment. As illustrations, we first consider phase engineering bosonic codes with uniform spacing in the Fock basis that correct excitation loss with a Kerr unitary and show that these modified codes feature destructive interference between error code words and, with an adapted “two-level” recovery, the error protection is significantly enhanced. We then study protection against energy decay with the presence of mode nonlinearities …
1 aLi, Linshu1 aYoung, Dylan, J1 aAlbert, Victor, V.1 aNoh, Kyungjoo1 aZou, Chang-Ling1 aJiang, Liang uhttps://authors.library.caltech.edu/109764/2/1901.05358.pdf01637nas a2200181 4500008004100000022001400041245010300055210006900158260001300227490000600240520106000246100002201306700002001328700002101348700002401369700002501393856003701418 2021 eng d a2643-156400aProtocols for estimating multiple functions with quantum sensor networks: Geometry and performance0 aProtocols for estimating multiple functions with quantum sensor c5/3/20210 v33 aWe consider the problem of estimating multiple analytic functions of a set of local parameters via qubit sensors in a quantum sensor network. To address this problem, we highlight a generalization of the sensor symmetric performance bounds of Rubio et. al. [J. Phys. A: Math. Theor. 53 344001 (2020)] and develop a new optimized sequential protocol for measuring such functions. We compare the performance of both approaches to one another and to local protocols that do not utilize quantum entanglement, emphasizing the geometric significance of the coefficient vectors of the measured functions in determining the best choice of measurement protocol. We show that, in many cases, especially for a large number of sensors, the optimized sequential protocol results in more accurate measurements than the other strategies. In addition, in contrast to the the sensor symmetric approach, the sequential protocol is known to always be explicitly implementable. The sequential protocol is very general and has a wide range of metrological applications.
1 aBringewatt, Jacob1 aBoettcher, Igor1 aNiroula, Pradeep1 aBienias, Przemyslaw1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2104.0954001237nas a2200253 4500008004100000245004100041210004100082260001300123520055200136100001900688700002400707700002100731700002000752700002700772700001800799700001600817700001700833700002000850700002100870700001900891700001300910700002300923856003700946 2021 eng d00aQuantum Machine Learning for Finance0 aQuantum Machine Learning for Finance c9/9/20213 aQuantum computers are expected to surpass the computational capabilities of classical computers during this decade, and achieve disruptive impact on numerous industry sectors, particularly finance. In fact, finance is estimated to be the first industry sector to benefit from Quantum Computing not only in the medium and long terms, but even in the short term. This review paper presents the state of the art of quantum algorithms for financial applications, with particular focus to those use cases that can be solved via Machine Learning.
1 aPistoia, Marco1 aAhmad, Syed, Farhan1 aAjagekar, Akshay1 aButs, Alexander1 aChakrabarti, Shouvanik1 aHerman, Dylan1 aHu, Shaohan1 aJena, Andrew1 aMinssen, Pierre1 aNiroula, Pradeep1 aRattew, Arthur1 aSun, Yue1 aYalovetzky, Romina uhttps://arxiv.org/abs/2109.0429802275nas 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 aQuantum 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/2102.1178402193nas 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 aThe 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/2004.0415101359nas a2200157 4500008004100000245003200041210003200073260001400105520093200119100002001051700002001071700002701091700002201118700002401140856003701164 2021 eng d00aSynchronous Values of Games0 aSynchronous Values of Games c9/29/20213 aWe study synchronous values of games, especially synchronous games. It is known that a synchronous game has a perfect strategy if and only if it has a perfect synchronous strategy. However, we give examples of synchronous games, in particular graph colouring games, with synchronous value that is strictly smaller than their ordinary value. Thus, the optimal strategy for a synchronous game need not be synchronous. We derive a formula for the synchronous value of an XOR game as an optimization problem over a spectrahedron involving a matrix related to the cost matrix. We give an example of a game such that the synchronous value of repeated products of the game is strictly increasing. We show that the synchronous quantum bias of the XOR of two XOR games is not multiplicative. Finally, we derive geometric and algebraic conditions that a set of projections that yields the synchronous value of a game must satisfy.
1 aHelton, William1 aMousavi, Hamoon1 aNezhadi, Seyed, Sajjad1 aPaulsen, Vern, I.1 aRussell, Travis, B. uhttps://arxiv.org/abs/2109.1474101465nas a2200169 4500008004100000245007200041210006900113260001400182520093400196100002301130700002001153700002501173700002101198700002101219700001801240856003701258 2021 eng d00aTight bounds on the convergence of noisy random circuits to uniform0 aTight bounds on the convergence of noisy random circuits to unif c12/1/20213 aWe study the properties of output distributions of noisy, random circuits. We obtain upper and lower bounds on the expected distance of the output distribution from the uniform distribution. These bounds are tight with respect to the dependence on circuit depth. Our proof techniques also allow us to make statements about the presence or absence of anticoncentration for both noisy and noiseless circuits. We uncover a number of interesting consequences for hardness proofs of sampling schemes that aim to show a quantum computational advantage over classical computation. Specifically, we discuss recent barrier results for depth-agnostic and/or noise-agnostic proof techniques. We show that in certain depth regimes, noise-agnostic proof techniques might still work in order to prove an often-conjectured claim in the literature on quantum computational advantage, contrary to what was thought prior to this work.
1 aDeshpande, Abhinav1 aFefferman, Bill1 aGorshkov, Alexey, V.1 aGullans, Michael1 aNiroula, Pradeep1 aShtanko, Oles uhttps://arxiv.org/abs/2112.0071601577nas a2200157 4500008004100000245006300041210006300104260001300167520107800180100003201258700002401290700002101314700002201335700002501357856003701382 2021 eng d00aUnifying Quantum and Classical Speed Limits on Observables0 aUnifying Quantum and Classical Speed Limits on Observables c8/9/20213 aThe presence of noise or the interaction with an environment can radically change the dynamics of observables of an otherwise isolated quantum system. We derive a bound on the speed with which observables of open quantum systems evolve. This speed limit divides into Mandalestam and Tamm's original time-energy uncertainty relation and a time-information uncertainty relation recently derived for classical systems, generalizing both to open quantum systems. By isolating the coherent and incoherent contributions to the system dynamics, we derive both lower and upper bounds to the speed of evolution. We prove that the latter provide tighter limits on the speed of observables than previously known quantum speed limits, and that a preferred basis of \emph{speed operators} serves to completely characterize the observables that saturate the speed limits. We use this construction to bound the effect of incoherent dynamics on the evolution of an observable and to find the Hamiltonian that gives the maximum coherent speedup to the evolution of an observable.
1 aGarcía-Pintos, Luis, Pedro1 aNicholson, Schuyler1 aGreen, Jason, R.1 adel Campo, Adolfo1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2108.0426101345nas a2200145 4500008004100000245006600041210006200107260001400169490000600183520092300189100001801112700001301130700001901143856003701162 2020 eng d00aApproximate Quantum Fourier Transform with O(nlog(n)) T gates0 aApproximate Quantum Fourier Transform with Onlogn T gates c3/13/20200 v63 aThe ability to implement the Quantum Fourier Transform (QFT) efficiently on a quantum computer enables the advantages offered by a variety of fundamental quantum algorithms, such as those for integer factoring, computing discrete logarithm over Abelian groups, and phase estimation. The standard fault-tolerant implementation of an n-qubit QFT approximates the desired transformation by removing small-angle controlled rotations and synthesizing the remaining ones into Clifford+t gates, incurring the t-count complexity of O(n log2 (n)). In this paper we show how to obtain approximate QFT with the t-count of O(n log(n)). Our approach relies on quantum circuits with measurements and feedforward, and on reusing a special quantum state that induces the phase gradient transformation. We report asymptotic analysis as well as concrete circuits, demonstrating significant advantages in both theory and practice.
1 aNam, Yunseong1 aSu, Yuan1 aMaslov, Dmitri uhttps://arxiv.org/abs/1803.0493302409nas a2200193 4500008004100000245006700041210006700108260001500175490000700190520183800197100002002035700001902055700002302074700001802097700002402115700002002139700001902159856003702178 2020 eng d00aContinuous symmetries and approximate quantum error correction0 aContinuous symmetries and approximate quantum error correction c10/26/20200 v103 aQuantum error correction and symmetry arise in many areas of physics, including many-body systems, metrology in the presence of noise, fault-tolerant computation, and holographic quantum gravity. Here we study the compatibility of these two important principles. If a logical quantum system is encoded into n physical subsystems, we say that the code is covariant with respect to a symmetry group G if a G transformation on the logical system can be realized by performing transformations on the individual subsystems. For a G-covariant code with G a continuous group, we derive a lower bound on the error correction infidelity following erasure of a subsystem. This bound approaches zero when the number of subsystems n or the dimension d of each subsystem is large. We exhibit codes achieving approximately the same scaling of infidelity with n or d as the lower bound. Leveraging tools from representation theory, we prove an approximate version of the Eastin-Knill theorem: If a code admits a universal set of transversal gates and corrects erasure with fixed accuracy, then, for each logical qubit, we need a number of physical qubits per subsystem that is inversely proportional to the error parameter. We construct codes covariant with respect to the full logical unitary group, achieving good accuracy for large d (using random codes) or n (using codes based on W-states). We systematically construct codes covariant with respect to general groups, obtaining natural generalizations of qubit codes to, for instance, oscillators and rotors. In the context of the AdS/CFT correspondence, our approach provides insight into how time evolution in the bulk corresponds to time evolution on the boundary without violating the Eastin-Knill theorem, and our five-rotor code can be stacked to form a covariant holographic code.
1 aFaist, Philippe1 aNezami, Sepehr1 aAlbert, Victor, V.1 aSalton, Grant1 aPastawski, Fernando1 aHayden, Patrick1 aPreskill, John uhttps://arxiv.org/abs/1902.0771401563nas a2200169 4500008004100000245002700041210002700068260001400095300001200109490000700121520114400128100002201272700002401294700001801318700002001336856003701356 2020 eng d00aDiscrete Time Crystals0 aDiscrete Time Crystals c3/10/2020 a467-4990 v113 aExperimental 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/1905.1323201465nas a2200265 4500008004100000245006700041210006500108260001500173490000800188520070100196100001800897700002200915700002500937700002400962700002500986700001801011700002101029700002001050700002501070700001601095700001701111700001501128700001901143856003701162 2020 eng d00aExperimental Low-Latency Device-Independent Quantum Randomness0 aExperimental LowLatency DeviceIndependent Quantum Randomness c12/24/20190 v1243 aApplications of randomness such as private key generation and public randomness beacons require small blocks of certified random bits on demand. Device-independent quantum random number generators can produce such random bits, but existing quantum-proof protocols and loophole-free implementations suffer from high latency, requiring many hours to produce any random bits. We demonstrate device-independent quantum randomness generation from a loophole-free Bell test with a more efficient quantum-proof protocol, obtaining multiple blocks of 512 bits with an average experiment time of less than 5 min per block and with certified error bounded by 2−64≈5.42×10−20.
1 aZhang, Yanbao1 aShalm, Lynden, K.1 aBienfang, Joshua, C.1 aStevens, Martin, J.1 aMazurek, Michael, D.1 aNam, Sae, Woo1 aAbellán, Carlos1 aAmaya, Waldimar1 aMitchell, Morgan, W.1 aFu, Honghao1 aMiller, Carl1 aMink, Alan1 aKnill, Emanuel uhttps://arxiv.org/abs/1812.0778602128nas a2200229 4500008004100000245006400041210006200105260001400167520146400181100001601645700002301661700001801684700002101702700001601723700002201739700002001761700001501781700002301796700001801819700002401837856003701861 2020 eng d00aFault-Tolerant Operation of a Quantum Error-Correction Code0 aFaultTolerant Operation of a Quantum ErrorCorrection Code c9/24/20203 aQuantum 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/2009.1148201576nas a2200157 4500008004100000245010800041210006900149260001400218490000600232520106400238100001701302700001601319700002701335700001901362856003701381 2020 eng d00aOptimal fermion-to-qubit mapping via ternary trees with applications to reduced quantum states learning0 aOptimal fermiontoqubit mapping via ternary trees with applicatio c5/26/20200 v43 aWe introduce a fermion-to-qubit mapping defined on ternary trees, where any single Majorana operator on an n-mode fermionic system is mapped to a multi-qubit Pauli operator acting nontrivially on ⌈log3(2n+1)⌉ qubits. The mapping has a simple structure and is optimal in the sense that it is impossible to construct Pauli operators in any fermion-to-qubit mapping acting nontrivially on less than log3(2n) qubits on average. We apply it to the problem of learning k-fermion reduced density matrix (RDM), a problem relevant in various quantum simulation applications. We show that using the ternary-tree mapping one can determine the elements of all k-fermion RDMs, to precision ϵ, by repeating a single quantum circuit for ≲(2n+1)kϵ−2 times. This result is based on a method we develop here that allows one to determine the elements of all k-qubit RDMs, to precision ϵ, by repeating a single quantum circuit for ≲3kϵ−2 times, independent of the system size. This improves over existing schemes for determining qubit RDMs.
1 aJiang, Zhang1 aKalev, Amir1 aMruczkiewicz, Wojciech1 aNeven, Hartmut uhttps://arxiv.org/abs/1910.1074601620nas a2200193 4500008004100000245006300041210006200104260001400166520106800180100001201248700001401260700001901274700002101293700002101314700001801335700001501353700002101368856003701389 2020 eng d00aProbing many-body localization on a noisy quantum computer0 aProbing manybody localization on a noisy quantum computer c6/22/20203 aA disordered system of interacting particles exhibits localized behavior when the disorder is large compared to the interaction strength. Studying this phenomenon on a quantum computer without error correction is challenging because even weak coupling to a thermal environment destroys most signatures of localization. Fortunately, spectral functions of local operators are known to contain features that can survive the presence of noise. In these spectra, discrete peaks and a soft gap at low frequencies compared to the thermal phase indicate localization. Here, we present the computation of spectral functions on a trapped-ion quantum computer for a one-dimensional Heisenberg model with disorder. Further, we design an error-mitigation technique which is effective at removing the noise from the measurement allowing clear signatures of localization to emerge as the disorder increases. Thus, we show that spectral functions can serve as a robust and scalable diagnostic of many-body localization on the current generation of quantum computers.
1 aZhu, D.1 aJohri, S.1 aNguyen, N., H.1 aAlderete, Huerta1 aLandsman, K., A.1 aLinke, N., M.1 aMonroe, C.1 aMatsuura, A., Y. uhttps://arxiv.org/abs/2006.1235501854nas 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 aThe 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/2001.0787701551nas 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 aThe 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/2002.0253701726nas a2200145 4500008004100000245006100041210006000102260001500162520126300177100002801440700003201468700002201500700002101522856003701543 2020 eng d00aTime-information uncertainty relations in thermodynamics0 aTimeinformation uncertainty relations in thermodynamics c09/21/20203 aPhysical systems that power motion and create structure in a fixed amount of time dissipate energy and produce entropy. Whether living or synthetic, systems performing these dynamic functions must balance dissipation and speed. Here, we show that rates of energy and entropy exchange are subject to a speed limit -- a time-information uncertainty relation -- imposed by the rates of change in the information content of the system. This uncertainty relation bounds the time that elapses before the change in a thermodynamic quantity has the same magnitude as its initial standard deviation. From this general bound, we establish a family of speed limits for heat, work, entropy production, and entropy flow depending on the experimental constraints on the system. In all of these inequalities, the time scale of transient dynamical fluctuations is universally bounded by the Fisher information. Moreover, they all have a mathematical form that mirrors the Mandelstam-Tamm version of the time-energy uncertainty relation in quantum mechanics. These bounds on the speed of arbitrary observables apply to transient systems away from thermodynamic equilibrium, independent of the physical assumptions about the stochastic dynamics or their function.
1 aNicholson, Schuyler, B.1 aGarcía-Pintos, Luis, Pedro1 adel Campo, Adolfo1 aGreen, Jason, R. uhttps://arxiv.org/abs/2001.0541802955nas a2200397 4500008004100000245008600041210006900127260001500196520181200211100002102023700002302044700002002067700001702087700002202104700001702126700002502143700001802168700001902186700001702205700001702222700002702239700001502266700001702281700001802298700001702316700001602333700002002349700001902369700002302388700002502411700002402436700001802460700002002478700002202498856003702520 2019 eng d00aDevelopment of Quantum InterConnects for Next-Generation Information Technologies0 aDevelopment of Quantum InterConnects for NextGeneration Informat c12/13/20193 aJust 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 aQuantum 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/1902.1017102093nas a2200145 4500008004100000245008200041210006900123260001500192490000800207520163800215100002101853700002101874700001501895856003701910 2019 eng d00aLimitations of semidefinite programs for separable states and entangled games0 aLimitations of semidefinite programs for separable states and en c03/04/20190 v3663 aSemidefinite programs (SDPs) are a framework for exact or approximate optimization that have widespread application in quantum information theory. We introduce a new method for using reductions to construct integrality gaps for SDPs. These are based on new limitations on the sum-of-squares (SoS) hierarchy in approximating two particularly important sets in quantum information theory, where previously no ω(1)-round integrality gaps were known: the set of separable (i.e. unentangled) states, or equivalently, the 2→4 norm of a matrix, and the set of quantum correlations; i.e. conditional probability distributions achievable with local measurements on a shared entangled state. In both cases no-go theorems were previously known based on computational assumptions such as the Exponential Time Hypothesis (ETH) which asserts that 3-SAT requires exponential time to solve. Our unconditional results achieve the same parameters as all of these previous results (for separable states) or as some of the previous results (for quantum correlations). In some cases we can make use of the framework of Lee-Raghavendra-Steurer (LRS) to establish integrality gaps for any SDP, not only the SoS hierarchy. Our hardness result on separable states also yields a dimension lower bound of approximate disentanglers, answering a question of Watrous and Aaronson et al. These results can be viewed as limitations on the monogamy principle, the PPT test, the ability of Tsirelson-type bounds to restrict quantum correlations, as well as the SDP hierarchies of Doherty-Parrilo-Spedalieri, Navascues-Pironio-Acin and Berta-Fawzi-Scholz.
1 aHarrow, Aram, W.1 aNatarajan, Anand1 aWu, Xiaodi uhttps://arxiv.org/abs/1612.0930602203nas a2200205 4500008004100000245008000041210006900121260001500190520157300205100002001778700002101798700002401819700001901843700001901862700001801881700002201899700001901921700002001940856003701960 2019 eng d00aQuantum Gravity in the Lab: Teleportation by Size and Traversable Wormholes0 aQuantum Gravity in the Lab Teleportation by Size and Traversable c2019/11/143 aWith the long-term goal of studying quantum gravity in the lab, we propose holographic teleportation protocols that can be readily executed in table-top experiments. These protocols exhibit similar behavior to that seen in recent traversable wormhole constructions: information that is scrambled into one half of an entangled system will, following a weak coupling between the two halves, unscramble into the other half. We introduce the concept of "teleportation by size" to capture how the physics of operator-size growth naturally leads to information transmission. The transmission of a signal through a semi-classical holographic wormhole corresponds to a rather special property of the operator-size distribution we call "size winding". For more general setups (which may not have a clean emergent geometry), we argue that imperfect size winding is a generalization of the traversable wormhole phenomenon. For example, a form of signalling continues to function at high temperature and at large times for generic chaotic systems, even though it does not correspond to a signal going through a geometrical wormhole, but rather to an interference effect involving macroscopically different emergent geometries. Finally, we outline implementations feasible with current technology in two experimental platforms: Rydberg atom arrays and trapped ions.
1 aBrown, Adam, R.1 aGharibyan, Hrant1 aLeichenauer, Stefan1 aLin, Henry, W.1 aNezami, Sepehr1 aSalton, Grant1 aSusskind, Leonard1 aSwingle, Brian1 aWalter, Michael uhttps://arxiv.org/abs/1911.0631402892nas a2200397 4500008004100000245005600041210005500097260001500152520177700167100001701944700002301961700002101984700002202005700001902027700001602046700001902062700002502081700002302106700002002129700002002149700002602169700002302195700002402218700002202242700002302264700001602287700001302303700002002316700002402336700001702360700001902377700001802396700002302414700002002437856003702457 2019 eng d00aQuantum Simulators: Architectures and Opportunities0 aQuantum Simulators Architectures and Opportunities c12/14/20193 aQuantum 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/1912.0693801664nas a2200157 4500008004100000245006600041210006200107260001500169520119400184100001801378700001901396700001701415700001901432700001801451856003701469 2019 eng d00aThe Speed of Quantum Information Spreading in Chaotic Systems0 aSpeed of Quantum Information Spreading in Chaotic Systems c08/19/20193 aWe present a general theory of quantum information propagation in chaotic quantum many-body systems. The generic expectation in such systems is that quantum information does not propagate in localized form; instead, it tends to spread out and scramble into a form that is inaccessible to local measurements. To characterize this spreading, we define an information speed via a quench-type experiment and derive a general formula for it as a function of the entanglement density of the initial state. As the entanglement density varies from zero to one, the information speed varies from the entanglement speed to the butterfly speed. We verify that the formula holds both for a quantum chaotic spin chain and in field theories with an AdS/CFT gravity dual. For the second case, we study in detail the dynamics of entanglement in two-sided Vaidya-AdS-Reissner-Nordstrom black branes. We also show that, with an appropriate decoding process, quantum information can be construed as moving at the information speed, and, in the case of AdS/CFT, we show that a locally detectable signal propagates at the information speed in a spatially local variant of the traversable wormhole setup.
1 aCouch, Josiah1 aEccles, Stefan1 aNguyen, Phuc1 aSwingle, Brian1 aXu, Shenglong uhttps://arxiv.org/abs/1908.0699301624nas a2200193 4500008004100000245009000041210006900131260001500200520100400215100001701219700002401236700001801260700001601278700002301294700002401317700002401341700002801365856003701393 2019 eng d00aToward convergence of effective field theory simulations on digital quantum computers0 aToward convergence of effective field theory simulations on digi c04/18/20193 aWe report results for simulating an effective field theory to compute the binding energy of the deuteron nucleus using a hybrid algorithm on a trapped-ion quantum computer. Two increasingly complex unitary coupled-cluster ansaetze have been used to compute the binding energy to within a few percent for successively more complex Hamiltonians. By increasing the complexity of the Hamiltonian, allowing more terms in the effective field theory expansion and calculating their expectation values, we present a benchmark for quantum computers based on their ability to scalably calculate the effective field theory with increasing accuracy. Our result of E4=−2.220±0.179MeV may be compared with the exact Deuteron ground-state energy −2.224MeV. We also demonstrate an error mitigation technique using Richardson extrapolation on ion traps for the first time. The error mitigation circuit represents a record for deepest quantum circuit on a trapped-ion quantum computer.
1 aShehab, Omar1 aLandsman, Kevin, A.1 aNam, Yunseong1 aZhu, Daiwei1 aLinke, Norbert, M.1 aKeesan, Matthew, J.1 aPooser, Raphael, C.1 aMonroe, Christopher, R. uhttps://arxiv.org/abs/1904.0433801295nas a2200169 4500008004100000245008000041210006900121260001500190490000600205520078500211100001800996700001901014700001301033700002301046700001901069856003701088 2018 eng d00aAutomated optimization of large quantum circuits with continuous parameters0 aAutomated optimization of large quantum circuits with continuous c2017/10/190 v43 aWe develop and implement automated methods for optimizing quantum circuits of the size and type expected in quantum computations that outperform classical computers. We show how to handle continuous gate parameters and report a collection of fast algorithms capable of optimizing large-scale quantum circuits. For the suite of benchmarks considered, we obtain substantial reductions in gate counts. In particular, we provide better optimization in significantly less time than previous approaches, while making minimal structural changes so as to preserve the basic layout of the underlying quantum algorithms. Our results help bridge the gap between the computations that can be run on existing hardware and those that are expected to outperform classical computers.
1 aNam, Yunseong1 aRoss, Neil, J.1 aSu, Yuan1 aChilds, Andrew, M.1 aMaslov, Dmitri uhttps://arxiv.org/abs/1710.0734501252nas a2200133 4500008004100000245006000041210005600101260001500157520084400172100002201016700002401038700001901062856003701081 2018 eng d00aAn autonomous single-piston engine with a quantum rotor0 aautonomous singlepiston engine with a quantum rotor c2018/02/153 aPistons 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/1802.0548605095nas 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 aSuperconductivity 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/1803.0411301662nas a2200217 4500008004100000245004200041210004000083260001500123300001200138490000600150520105500156100002101211700002201232700002101254700002201275700002301297700001601320700001901336700001601355856007301371 2018 eng d00aElectro-mechano-optical NMR detection0 aElectromechanooptical NMR detection c2018/02/01 a152-1580 v53 aSignal 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-5-2-15201648nas a2200169 4500008004100000245006500041210006400106260001500170300000700185520110300192100001701295700002101312700002601333700002501359700001901384856007501403 2018 eng d00aEntanglement of purification: from spin chains to holography0 aEntanglement of purification from spin chains to holography c2018/01/22 a983 aPurification is a powerful technique in quantum physics whereby a mixed quantum state is extended to a pure state on a larger system. This process is not unique, and in systems composed of many degrees of freedom, one natural purification is the one with minimal entanglement. Here we study the entropy of the minimally entangled purification, called the entanglement of purification, in three model systems: an Ising spin chain, conformal field theories holographically dual to Einstein gravity, and random stabilizer tensor networks. We conjecture values for the entanglement of purification in all these models, and we support our conjectures with a variety of numerical and analytical results. We find that such minimally entangled purifications have a number of applications, from enhancing entanglement-based tensor network methods for describing mixed states to elucidating novel aspects of the emergence of geometry from entanglement in the AdS/CFT correspondence.
1 aNguyen, Phuc1 aDevakul, Trithep1 aHalbasch, Matthew, G.1 aZaletel, Michael, P.1 aSwingle, Brian uhttps://link.springer.com/article/10.1007%2FJHEP01%282018%29098#citeas02638nas a2200265 4500008004100000245009500041210006900136260001500205300001200220490000800232520186000240100002102100700001902121700001802140700001802158700001502176700002002191700001902211700001602230700002502246700001802271700002402289700002202313856003702335 2018 eng d00aExperimentally Generated Randomness Certified by the Impossibility of Superluminal Signals0 aExperimentally Generated Randomness Certified by the Impossibili c2018/04/11 a223-2260 v5563 aFrom dice to modern complex circuits, there have been many attempts to build increasingly better devices to generate random numbers. Today, randomness is fundamental to security and cryptographic systems, as well as safeguarding privacy. A key challenge with random number generators is that it is hard to ensure that their outputs are unpredictable. For a random number generator based on a physical process, such as a noisy classical system or an elementary quantum measurement, a detailed model describing the underlying physics is required to assert unpredictability. Such a model must make a number of assumptions that may not be valid, thereby compromising the integrity of the device. However, it is possible to exploit the phenomenon of quantum nonlocality with a loophole-free Bell test to build a random number generator that can produce output that is unpredictable to any adversary limited only by general physical principles. With recent technological developments, it is now possible to carry out such a loophole-free Bell test. Here we present certified randomness obtained from a photonic Bell experiment and extract 1024 random bits uniform to within 10−12. These random bits could not have been predicted within any physical theory that prohibits superluminal signaling and allows one to make independent measurement choices. To certify and quantify the randomness, we describe a new protocol that is optimized for apparatuses characterized by a low per-trial violation of Bell inequalities. We thus enlisted an experimental result that fundamentally challenges the notion of determinism to build a system that can increase trust in random sources. In the future, random number generators based on loophole-free Bell tests may play a role in increasing the security and trust of our cryptographic systems and infrastructure.
1 aBierhorst, Peter1 aKnill, Emanuel1 aGlancy, Scott1 aZhang, Yanbao1 aMink, Alan1 aJordan, Stephen1 aRommal, Andrea1 aLiu, Yi-Kai1 aChristensen, Bradley1 aNam, Sae, Woo1 aStevens, Martin, J.1 aShalm, Lynden, K. uhttps://arxiv.org/abs/1803.0621901224nas a2200145 4500008004100000245008400041210006900125520074800194100001700942700001900959700001800978700002900996700001601025856003701041 2018 eng d00aMore is Less: Perfectly Secure Oblivious Algorithms in the Multi-Server Setting0 aMore is Less Perfectly Secure Oblivious Algorithms in the MultiS3 aThe problem of Oblivious RAM (ORAM) has traditionally been studied in a single-server setting, but more recently the multi-server setting has also been considered. Yet it is still unclear whether the multi-server setting has any inherent advantages, e.g., whether the multi-server setting can be used to achieve stronger security goals or provably better efficiency than is possible in the single-server case. In this work, we construct a perfectly secure 3-server ORAM scheme that outperforms the best known single-server scheme by a logarithmic factor. In the process, we also show, for the first time, that there exist specific algorithms for which multiple servers can overcome known lower bounds in the single-server setting.
1 aChan, Hubert1 aKatz, Jonathan1 aNayak, Kartik1 aPolychroniadou, Antigoni1 aShi, Elaine uhttps://arxiv.org/abs/1809.0082501252nas a2200157 4500008004100000245003400041210002700075260000900102490000800111520082700119100001900946700002300965700002300988700002101011856006201032 2018 eng d00aOn the need for soft dressing0 aneed for soft dressing c20180 v1213 aIn order to deal with IR divergences arising in QED or perturbative quantum gravity scattering processes, one can either calculate inclusive quantities or use dressed asymptotic states. We consider incoming superpositions of momentum eigenstates and show that in calculations of cross-sections these two approaches yield different answers: in the inclusive formalism no interference occurs for incoming finite superpositions and wavepackets do not scatter at all, while the dressed formalism yields the expected interference terms. This suggests that rather than Fock space states, one should use Faddeev-Kulish-type dressed states to correctly describe physical processes involving incoming superpositions. We interpret this in terms of selection rules due to large U(1) gauge symmetries and BMS supertranslations.
1 aCarney, Daniel1 aChaurette, Laurent1 aNeuenfeld, Dominik1 aSemenoff, Gordon uhttps://www.quics.umd.edu/publications/need-soft-dressing02023nas 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 aBound 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/359/6377/78301599nas a2200133 4500008004100000245006800041210006800109520117300177100001801350700002001368700002001388700002001408856003701428 2018 eng d00aQuantum Supremacy and the Complexity of Random Circuit Sampling0 aQuantum Supremacy and the Complexity of Random Circuit Sampling3 aA critical milestone on the path to useful quantum computers is quantum supremacy - a demonstration of a quantum computation that is prohibitively hard for classical computers. A leading near-term candidate, put forth by the Google/UCSB team, is sampling from the probability distributions of randomly chosen quantum circuits, which we call Random Circuit Sampling (RCS). In this paper we study both the hardness and verification of RCS. While RCS was defined with experimental realization in mind, we show complexity theoretic evidence of hardness that is on par with the strongest theoretical proposals for supremacy. Specifically, we show that RCS satisfies an average-case hardness condition - computing output probabilities of typical quantum circuits is as hard as computing them in the worst-case, and therefore #P-hard. Our reduction exploits the polynomial structure in the output amplitudes of random quantum circuits, enabled by the Feynman path integral. In addition, it follows from known results that RCS satisfies an anti-concentration property, making it the first supremacy proposal with both average-case hardness and anti-concentration.
1 aBouland, Adam1 aFefferman, Bill1 aNirkhe, Chinmay1 aVazirani, Umesh uhttps://arxiv.org/abs/1803.0440201648nas a2200169 4500008004100000245006100041210006100102300001400163490000900177520116300186100002301349700001901372700001801391700001901409700001301428856003701441 2018 eng d00aToward the first quantum simulation with quantum speedup0 aToward the first quantum simulation with quantum speedup a9456-94610 v115 3 aWith quantum computers of significant size now on the horizon, we should understand how to best exploit their initially limited abilities. To this end, we aim to identify a practical problem that is beyond the reach of current classical computers, but that requires the fewest resources for a quantum computer. We consider quantum simulation of spin systems, which could be applied to understand condensed matter phenomena. We synthesize explicit circuits for three leading quantum simulation algorithms, using diverse techniques to tighten error bounds and optimize circuit implementations. Quantum signal processing appears to be preferred among algorithms with rigorous performance guarantees, whereas higher-order product formulas prevail if empirical error estimates suffice. Our circuits are orders of magnitude smaller than those for the simplest classically infeasible instances of factoring and quantum chemistry, bringing practical quantum computation closer to reality.
1 aChilds, Andrew, M.1 aMaslov, Dmitri1 aNam, Yunseong1 aRoss, Neil, J.1 aSu, Yuan uhttps://arxiv.org/abs/1711.1098002145nas a2200205 4500008004100000245005800041210005700099260001500156300001100171490000700182520152100189100002301710700002101733700002201754700002101776700002501797700002101822700002701843856006901870 2017 eng d00aEmergent equilibrium in many-body optical bistability0 aEmergent equilibrium in manybody optical bistability c2017/04/17 a0438260 v953 aMany-body systems constructed of quantum-optical building blocks can now be realized in experimental platforms ranging from exciton-polariton fluids to ultracold gases of Rydberg atoms, establishing a fascinating interface between traditional many-body physics and the driven-dissipative, non-equilibrium setting of cavity-QED. At this interface, the standard techniques and intuitions of both fields are called into question, obscuring issues as fundamental as the role of fluctuations, dimensionality, and symmetry on the nature of collective behavior and phase transitions. Here, we study the driven-dissipative Bose-Hubbard model, a minimal description of numerous atomic, optical, and solid-state systems in which particle loss is countered by coherent driving. Despite being a lattice version of optical bistability---a foundational and patently non-equilibrium model of cavity-QED---the steady state possesses an emergent equilibrium description in terms of a classical Ising model. We establish this picture by identifying a limit in which the quantum dynamics is asymptotically equivalent to non-equilibrium Langevin equations, which support a phase transition described by model A of the Hohenberg-Halperin classification. Numerical simulations of the Langevin equations corroborate this picture, producing results consistent with the behavior of a finite-temperature Ising model.
1 aFoss-Feig, Michael1 aNiroula, Pradeep1 aYoung, Jeremy, T.1 aHafezi, Mohammad1 aGorshkov, Alexey, V.1 aWilson, Ryan, M.1 aMaghrebi, Mohammad, F. uhttps://journals.aps.org/pra/abstract/10.1103/PhysRevA.95.04382601575nas a2200217 4500008004100000245010100041210006900142260001500211520089600226100002101122700001901143700001801162700001501180700002401195700001901219700001601238700002501254700001801279700002201297856003801319 2017 eng d00aExperimentally Generated Random Numbers Certified by the Impossibility of Superluminal Signaling0 aExperimentally Generated Random Numbers Certified by the Impossi c2017/02/163 aRandom numbers are an important resource for applications such as numerical simulation and secure communication. However, it is difficult to certify whether a physical random number generator is truly unpredictable. Here, we exploit the phenomenon of quantum nonlocality in a loophole-free photonic Bell test experiment for the generation of randomness that cannot be predicted within any physical theory that allows one to make independent measurement choices and prohibits superluminal signaling. To certify and quantify the randomness, we describe a new protocol that performs well in an experimental regime characterized by low violation of Bell inequalities. Applying an extractor function to our data, we obtained 256 new random bits, uniform to within 0.001.
1 aBierhorst, Peter1 aKnill, Emanuel1 aGlancy, Scott1 aMink, Alan1 aJordan, Stephen, P.1 aRommal, Andrea1 aLiu, Yi-Kai1 aChristensen, Bradley1 aNam, Sae, Woo1 aShalm, Lynden, K. uhttps://arxiv.org/abs/1702.05178#14878nas a2200157 45000080041000000220014000412450074000552100069001292600015001983000008002134900007002215201439400228100001814622700001614640856006414656 2017 eng d a1573-133200aOptimal length of decomposition sequences composed of imperfect gates0 aOptimal length of decomposition sequences composed of imperfect c2017/03/24 a1230 v163 aQuantum error correcting circuitry is both a resource for correcting errors and a source for generating errors. A balance has to be struck between these two aspects. Perfect quantum gates do not exist in nature. Therefore, it is important to investigate how flaws in the quantum hardware affect quantum computing performance. We do this in two steps. First, in the presence of realistic, faulty quantum hardware, we establish how quantum error correction circuitry achieves reduction in the extent of quantum information corruption. Then, we investigate fault-tolerant gate sequence techniques that result in an approximate phase rotation gate, and establish the existence of an optimal length of the length L of the decomposition sequence. The existence of is due to the competition between the increase in gate accuracy with increasing L, but the decrease in gate performance due to the diffusive proliferation of gate errors due to faulty basis gates. We present an analytical formula for the gate fidelity as a function of L that is in satisfactory agreement with the results of our simulations and allows the determination of via the solution of a transcendental equation. Our result is universally applicable since gate sequence approximations also play an important role, e.g., in atomic and molecular physics and in nuclear magnetic resonance.
1 aNam, Yunseong1 aBlümel, R. uhttps://link.springer.com/article/10.1007/s11128-017-1571-502646nas a2200241 4500008004100000245008200041210006900123260001500192520190700207100002902114700002302143700001802166700002302184700001502207700002002222700002702242700002402269700001902293700002002312700001702332700001802349856003702367 2017 eng d00aOn the readiness of quantum optimization machines for industrial applications0 areadiness of quantum optimization machines for industrial applic c2017/08/313 aThere have been multiple attempts to demonstrate that quantum annealing and, in particular, quantum annealing on quantum annealing machines, has the potential to outperform current classical optimization algorithms implemented on CMOS technologies. The benchmarking of these devices has been controversial. Initially, random spin-glass problems were used, however, these were quickly shown to be not well suited to detect any quantum speedup. Subsequently, benchmarking shifted to carefully crafted synthetic problems designed to highlight the quantum nature of the hardware while (often) ensuring that classical optimization techniques do not perform well on them. Even worse, to date a true sign of improved scaling with the number problem variables remains elusive when compared to classical optimization techniques. Here, we analyze the readiness of quantum annealing machines for real-world application problems. These are typically not random and have an underlying structure that is hard to capture in synthetic benchmarks, thus posing unexpected challenges for optimization techniques, both classical and quantum alike. We present a comprehensive computational scaling analysis of fault diagnosis in digital circuits, considering architectures beyond D-wave quantum annealers. We find that the instances generated from real data in multiplier circuits are harder than other representative random spin-glass benchmarks with a comparable number of variables. Although our results show that transverse-field quantum annealing is outperformed by state-of-the-art classical optimization algorithms, these benchmark instances are hard and small in the size of the input, therefore representing the first industrial application ideally suited for near-term quantum annealers.
1 aPerdomo-Ortiz, Alejandro1 aFeldman, Alexander1 aOzaeta, Asier1 aIsakov, Sergei, V.1 aZhu, Zheng1 aO'Gorman, Bryan1 aKatzgraber, Helmut, G.1 aDiedrich, Alexander1 aNeven, Hartmut1 ade Kleer, Johan1 aLackey, Brad1 aBiswas, Rupak uhttps://arxiv.org/abs/1708.0978000962nas a2200121 4500008004100000245007400041210006900115260001500184520054100199100001900740700001800759856006300777 2017 eng d00aUse of global interactions in efficient quantum circuit constructions0 aUse of global interactions in efficient quantum circuit construc c2017/12/213 aIn this paper we study the ways to use a global entangling operator to efficiently implement circuitry common to a selection of important quantum algorithms. In particular, we focus on the circuits composed with global Ising entangling gates and arbitrary addressable single-qubit gates. We show that under certain circumstances the use of global operations can substantially improve the entangling gate count.
1 aMaslov, Dmitri1 aNam, Yunseong uhttp://iopscience.iop.org/article/10.1088/1367-2630/aaa39801247nas a2200169 4500008004100000245005400041210005400095260001500149300001200164520072500176100002400901700002000925700002100945700001600966700001800982856007701000 2016 eng d00aHigh resolution adaptive imaging of a single atom0 aHigh resolution adaptive imaging of a single atom c2016/07/18 a606-6103 aWe report the optical imaging of a single atom with nanometer resolution using an adaptive optical alignment technique that is applicable to general optical microscopy. By decomposing the image of a single laser-cooled atom, we identify and correct optical aberrations in the system and realize an atomic position sensitivity of ≈ 0.5 nm/Hz−−−√ with a minimum uncertainty of 1.7 nm, allowing the direct imaging of atomic motion. This is the highest position sensitivity ever measured for an isolated atom, and opens up the possibility of performing out-of-focus 3D particle tracking, imaging of atoms in 3D optical lattices or sensing forces at the yoctonewton (10−24 N) scale.
1 aWong-Campos, J., D.1 aJohnson, K., G.1 aNeyenhuis, Brian1 aMizrahi, J.1 aMonroe, Chris uhttps://www.nature.com/nphoton/journal/v10/n9/full/nphoton.2016.136.html01583nas a2200145 4500008004100000245006900041210006900110260001500179300001100194490000900205520112300214100002301337700002301360856005401383 2016 eng d00aLattice Laughlin states on the torus from conformal field theory0 aLattice Laughlin states on the torus from conformal field theory c2016/01/28 a0131020 v20163 aConformal field theory has turned out to be a powerful tool to derive two-dimensional lattice models displaying fractional quantum Hall physics. So far most of the work has been for lattices with open boundary conditions in at least one of the two directions, but it is desirable to also be able to handle the case of periodic boundary conditions. Here, we take steps in this direction by deriving analytical expressions for a family of conformal field theory states on the torus that is closely related to the family of bosonic and fermionic Laughlin states. We compute how the states transform when a particle is moved around the torus and when the states are translated or rotated, and we provide numerical evidence in particular cases that the states become orthonormal up to a common factor for large lattices. We use these results to find the S -matrix of the states, which turns out to be the same as for the continuum Laughlin states. Finally, we show that when the states are defined on a square lattice with suitable lattice spacing they practically coincide with the Laughlin states restricted to a lattice.1 aDeshpande, Abhinav1 aNielsen, Anne, E B uhttp://stacks.iop.org/1742-5468/2016/i=1/a=01310202166nas 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 aWhen 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/1508.07026v102050nas a2200205 4500008004100000245008900041210006900130260001500199520143900214100001801653700001401671700001601685700001401701700001701715700001701732700001801749700002501767700001501792856003701807 2016 eng d00a{O}bservation of {P}rethermalization in {L}ong-{R}ange {I}nteracting {S}pin {C}hains0 aO bservation of P rethermalization in L ong R ange I nteracting c2016/08/023 aStatistical mechanics can predict thermal equilibrium states for most classical systems, but for an isolated quantum system there is no general understanding on how equilibrium states dynamically emerge from the microscopic Hamiltonian. For instance, quantum systems that are near-integrable usually fail to thermalize in an experimentally realistic time scale and, instead, relax to quasi-stationary prethermal states that can be described by statistical mechanics when approximately conserved quantities are appropriately included in a generalized Gibbs ensemble (GGE). Here we experimentally study the relaxation dynamics of a chain of up to 22 spins evolving under a long-range transverse field Ising Hamiltonian following a sudden quench. For sufficiently long-ranged interactions the system relaxes to a new type of prethermal state that retains a strong memory of the initial conditions. In this case, the prethermal state cannot be described by a GGE, but rather arises from an emergent double-well potential felt by the spin excitations. This result shows that prethermalization occurs in a significantly broader context than previously thought, and reveals new challenges for a generic understanding of the thermalization of quantum systems, particularly in the presence of long-range interactions.
1 aNeyenhuis, B.1 aSmith, J.1 aLee, A., C.1 aZhang, J.1 aRicherme, P.1 aHess, P., W.1 aGong, Z., -X.1 aGorshkov, Alexey, V.1 aMonroe, C. uhttps://arxiv.org/abs/1608.0068121161nas a2200205 45000080041000000200022000410220014000632450069000772100068001462600015002143000016002294900007002455202053400252100002020786700002420806700002420830700002220854700002520876856005420901 2016 eng d a978-3-95977-013-2 a1868-896900aSpace-Efficient Error Reduction for Unitary Quantum Computations0 aSpaceEfficient Error Reduction for Unitary Quantum Computations c2016/04/27 a14:1--14:140 v553 aThis paper develops general space-efficient methods for error reduction for unitary quantum computation. Consider a polynomial-time quantum computation with completeness
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/1602.0097900877nas a2200181 4500008004100000245002200041210002200063260001500085300001200100490000700112520044800119100002300567700001800590700001800608700001800626700001400644856003700658 2015 eng d00aMomentum switches0 aMomentum switches c2015/05/01 a601-6210 v153 a Certain continuous-time quantum walks can be viewed as scattering processes. These processes can perform quantum computations, but it is challenging to design graphs with desired scattering behavior. In this paper, we study and construct momentum switches, graphs that route particles depending on their momenta. We also give an example where there is no exact momentum switch, although we construct an arbitrarily good approximation. 1 aChilds, Andrew, M.1 aGosset, David1 aNagaj, Daniel1 aRaha, Mouktik1 aWebb, Zak uhttp://arxiv.org/abs/1406.4510v101328nas 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/1412.8473v101151nas a2200145 4500008004100000245005800041210005700099260001300156490000800169520073200177100002500909700001700934700001700951856003700968 2013 eng d00aDissipative Many-body Quantum Optics in Rydberg Media0 aDissipative Manybody Quantum Optics in Rydberg Media c2013/4/90 v1103 a We develop a theoretical framework for the dissipative propagation of quantized light in interacting optical media under conditions of electromagnetically induced transparency (EIT). The theory allows us to determine the peculiar spatiotemporal structure of the output of two complementary Rydberg-EIT-based light-processing modules: the recently demonstrated single-photon filter and the recently proposed single-photon subtractor, which, respectively, let through and absorb a single photon. In addition to being crucial for applications of these and other optical quantum devices, the theory opens the door to the study of exotic dissipative many-body dynamics of strongly interacting photons in nonlinear nonlocal media. 1 aGorshkov, Alexey, V.1 aNath, Rejish1 aPohl, Thomas uhttp://arxiv.org/abs/1211.7060v101021nas a2200169 4500008004100000245009300041210006900134260001500203300001200218490000700230520048600237100002400723700002400747700001800771700002500789856003700814 2012 eng d00aAchieving perfect completeness in classical-witness quantum Merlin-Arthur proof systems0 aAchieving perfect completeness in classicalwitness quantum Merli c2012/05/01 a461-4710 v123 a This paper proves that classical-witness quantum Merlin-Arthur proof systems can achieve perfect completeness. That is, QCMA = QCMA1. This holds under any gate set with which the Hadamard and arbitrary classical reversible transformations can be exactly implemented, e.g., {Hadamard, Toffoli, NOT}. The proof is quantumly nonrelativizing, and uses a simple but novel quantum technique that additively adjusts the success probability, which may be of independent interest. 1 aJordan, Stephen, P.1 aKobayashi, Hirotada1 aNagaj, Daniel1 aNishimura, Harumichi uhttp://arxiv.org/abs/1111.5306v201519nas a2200217 4500008004100000245008300041210006900124260001400193490000800207520087700215100002001092700002101112700002201133700001201155700002101167700002301188700002001211700002101231700001201252856003701264 2012 eng d00aLong-lived dipolar molecules and Feshbach molecules in a 3D optical lattice 0 aLonglived dipolar molecules and Feshbach molecules in a 3D optic c2012/2/230 v1083 a We have realized long-lived ground-state polar molecules in a 3D optical lattice, with a lifetime of up to 25 s, which is limited only by off-resonant scattering of the trapping light. Starting from a 2D optical lattice, we observe that the lifetime increases dramatically as a small lattice potential is added along the tube-shaped lattice traps. The 3D optical lattice also dramatically increases the lifetime for weakly bound Feshbach molecules. For a pure gas of Feshbach molecules, we observe a lifetime of >20 s in a 3D optical lattice; this represents a 100-fold improvement over previous results. This lifetime is also limited by off-resonant scattering, the rate of which is related to the size of the Feshbach molecule. Individually trapped Feshbach molecules in the 3D lattice can be converted to pairs of K and Rb atoms and back with nearly 100% efficiency. 1 aChotia, Amodsen1 aNeyenhuis, Brian1 aMoses, Steven, A.1 aYan, Bo1 aCovey, Jacob, P.1 aFoss-Feig, Michael1 aRey, Ana, Maria1 aJin, Deborah, S.1 aYe, Jun uhttp://arxiv.org/abs/1110.4420v101592nas a2200205 4500008004100000245012500041210006900166260001500235520091800250100001801168700002001186700002601206700002001232700001901252700001901271700001801290700002101308700002001329856003701349 2012 eng d00aPhotonic quantum simulation of ground state configurations of Heisenberg square and checkerboard lattice spin systems 0 aPhotonic quantum simulation of ground state configurations of He c2012/05/123 a Photonic quantum simulators are promising candidates for providing insight into other small- to medium-sized quantum systems. The available photonic quantum technology is reaching the state where significant advantages arise for the quantum simulation of interesting questions in Heisenberg spin systems. Here we experimentally simulate such spin systems with single photons and linear optics. The effective Heisenberg-type interactions among individual single photons are realized by quantum interference at the tunable direction coupler followed by the measurement process. The effective interactions are characterized by comparing the entanglement dynamics using pairwise concurrence of a four-photon quantum system. We further show that photonic quantum simulations of generalized Heisenberg interactions on a four-site square lattice and a six-site checkerboard lattice are in reach of current technology. 1 aMa, Xiao-song1 aDakic, Borivoje1 aKropatsche, Sebastian1 aNaylor, William1 aChan, Yang-hao1 aGong, Zhe-Xuan1 aDuan, Lu-ming1 aZeilinger, Anton1 aWalther, Philip uhttp://arxiv.org/abs/1205.2801v101526nas a2200157 4500008004100000245005100041210005000092260001500142520108300157100002201240700001901262700001701281700001601298700001701314856003701331 2011 eng d00aContinuous-variable quantum compressed sensing0 aContinuousvariable quantum compressed sensing c2011/11/033 a We significantly extend recently developed methods to faithfully reconstruct unknown quantum states that are approximately low-rank, using only a few measurement settings. Our new method is general enough to allow for measurements from a continuous family, and is also applicable to continuous-variable states. As a technical result, this work generalizes quantum compressed sensing to the situation where the measured observables are taken from a so-called tight frame (rather than an orthonormal basis) --- hence covering most realistic measurement scenarios. As an application, we discuss the reconstruction of quantum states of light from homodyne detection and other types of measurements, and we present simulations that show the advantage of the proposed compressed sensing technique over present methods. Finally, we introduce a method to construct a certificate which guarantees the success of the reconstruction with no assumption on the state, and we show how slightly more measurements give rise to "universal" state reconstruction that is highly robust to noise. 1 aOhliger, Matthias1 aNesme, Vincent1 aGross, David1 aLiu, Yi-Kai1 aEisert, Jens uhttp://arxiv.org/abs/1111.0853v301407nas 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/1011.5616v201416nas a2200145 4500008004100000245014100041210006900182260001400251490000700265520088800272100002801160700002501188700002001213856003701233 2011 eng d00aLight storage in an optically thick atomic ensemble under conditions of electromagnetically induced transparency and four-wave mixing 0 aLight storage in an optically thick atomic ensemble under condit c2011/6/200 v833 a We study the modification of a traditional electromagnetically induced transparency (EIT) stored light technique that includes both EIT and four-wave mixing (FWM) in an ensemble of hot Rb atoms. The standard treatment of light storage involves the coherent and reversible mapping of one photonic mode onto a collective spin coherence. It has been shown that unwanted, competing processes such as four-wave mixing are enhanced by EIT and can significantly modify the signal optical pulse propagation. We present theoretical and experimental evidence to indicate that while a Stokes field is indeed detected upon retrieval of the signal field, any information originally encoded in a seeded Stokes field is not independently preserved during the storage process. We present a simple model that describes the propagation dynamics of the fields and the impact of FWM on the spin wave. 1 aPhillips, Nathaniel, B.1 aGorshkov, Alexey, V.1 aNovikova, Irina uhttp://arxiv.org/abs/1103.2131v102052nas 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/1009.2267v100539nas a2200133 4500008004100000245014600041210006900187300000900256490000700265100001900272700002500291700001600316856007300332 2009 eng d00aSlow light propagation and amplification via electromagnetically induced transparency and four-wave mixing in an optically dense atomic vapor0 aSlow light propagation and amplification via electromagnetically a19160 v561 aPhillips, N, B1 aGorshkov, Alexey, V.1 aNovikova, I uhttp://www.informaworld.com/smpp/content db=all content=a91354540501341nas a2200145 4500008004100000245004200041210004200083260001300125490000700138520094000145100002801085700002501113700002001138856003701158 2008 eng d00aOptimal light storage in atomic vapor0 aOptimal light storage in atomic vapor c2008/8/10 v783 a We study procedures for the optimization of efficiency of light storage and retrieval based on the dynamic form of electromagnetically induced transparency (EIT) in warm Rb vapor. We present a detailed analysis of two recently demonstrated optimization protocols: a time-reversal-based iteration procedure, which finds the optimal input signal pulse shape for any given control field, and a procedure based on the calculation of an optimal control field for any given signal pulse shape. We verify that the two procedures are consistent with each other, and that they both independently achieve the maximum memory efficiency for any given optical depth. We observe good agreement with theoretical predictions for moderate optical depths (<25), while at higher optical depths the experimental efficiency falls below the theoretically predicted values. We identify possible effects responsible for this reduction in memory efficiency. 1 aPhillips, Nathaniel, B.1 aGorshkov, Alexey, V.1 aNovikova, Irina uhttp://arxiv.org/abs/0805.3348v100956nas a2200145 4500008004100000245005600041210005600097260001400153490000700167520052600174100002000700700002800720700002500748856003700773 2008 eng d00aOptimal light storage with full pulse shape control0 aOptimal light storage with full pulse shape control c2008/8/200 v783 a We experimentally demonstrate optimal storage and retrieval of light pulses of arbitrary shape in atomic ensembles. By shaping auxiliary control pulses, we attain efficiencies approaching the fundamental limit and achieve precise retrieval into any predetermined temporal profile. Our techniques, demonstrated in warm Rb vapor, are applicable to a wide range of systems and protocols. As an example, we present their potential application to the creation of optical time-bin qubits and to controlled partial retrieval. 1 aNovikova, Irina1 aPhillips, Nathaniel, B.1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/0805.1927v100417nas a2200133 4500008004100000245005600041210005500097300001400152490000700166100001600173700001900189700002500208856005000233 2008 eng d00aOptimal light storage with full pulse-shape control0 aOptimal light storage with full pulseshape control a021802(R)0 v781 aNovikova, I1 aPhillips, N, B1 aGorshkov, Alexey, V. uhttp://link.aps.org/abstract/PRA/v78/e021802/00824nas a2200205 4500008004100000245007200041210006900113300001100182490000900193100001300202700001200215700002500227700001600252700001600268700001900284700001900303700001600322700002000338856026000358 2008 eng d00aOptimizing Slow and Stored Light for Multidisciplinary Applications0 aOptimizing Slow and Stored Light for Multidisciplinary Applicati a69040C0 v69041 aKlein, M1 aXiao, Y1 aGorshkov, Alexey, V.1 aHohensee, M1 aLeung, C, D1 aBrowning, M, R1 aPhillips, D, F1 aNovikova, I1 aWalsworth, R, L uhttp://spie.org/x648.xml?product_id=772216&Search_Origin=QuickSearch&Search_Results_URL=http://spie.org/x1636.xml&Alternate_URL=http://spie.org/x18509.xml&Alternate_URL_Name=timeframe&Alternate_URL_Value=Exhibitors&UseJavascript=1&Please_Wait_URL=http://s01063nas 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/0707.2963v201051nas 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/0607140v200706nas a2200181 4500008004100000245009700041210006900138300001100207490000900218100001500227700001800242700001700260700002500277700001700302700001700319700001600336856017200352 2007 eng d00aMulti-photon Entanglement: From Quantum Curiosity to Quantum Computing and Quantum Repeaters0 aMultiphoton Entanglement From Quantum Curiosity to Quantum Compu a66640G0 v66641 aWalther, P1 aEisaman, M, D1 aNemiroski, A1 aGorshkov, Alexey, V.1 aZibrov, A, S1 aZeilinger, A1 aLukin, M, D uhttp://spiedigitallibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PSISDG00666400000166640G000001&idtype=cvips&gifs=Yes&bproc=volrange&scode=6600%20-%20669900984nas a2200181 4500008004100000245005700041210005700098260001400155490000700169520043900176100002000615700002500635700002400660700002500684700002300709700002600732856004400758 2007 eng d00aOptimal control of light pulse storage and retrieval0 aOptimal control of light pulse storage and retrieval c2007/6/150 v983 a We demonstrate experimentally a procedure to obtain the maximum efficiency for the storage and retrieval of light pulses in atomic media. The procedure uses time reversal to obtain optimal input signal pulse-shapes. Experimental results in warm Rb vapor are in good agreement with theoretical predictions and demonstrate a substantial improvement of efficiency. This optimization procedure is applicable to a wide range of systems. 1 aNovikova, Irina1 aGorshkov, Alexey, V.1 aPhillips, David, F.1 aSorensen, Anders, S.1 aLukin, Mikhail, D.1 aWalsworth, Ronald, L. uhttp://arxiv.org/abs/quant-ph/0702266v100624nas a2200169 4500008004100000245005800041210005800099300001100157490000900168100001600177700002500193700001900218700001200237700001300249700002000262856017200282 2007 eng d00aOptimization of slow and stored light in atomic vapor0 aOptimization of slow and stored light in atomic vapor a64820M0 v64821 aNovikova, I1 aGorshkov, Alexey, V.1 aPhillips, D, F1 aXiao, Y1 aKlein, M1 aWalsworth, R, L uhttp://spiedigitallibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PSISDG00648200000164820M000001&idtype=cvips&gifs=Yes&bproc=volrange&scode=6400%20-%20649901341nas a2200145 4500008004100000245007700041210006900118260001400187490000700201520087300208100002301081700002201104700002501126856004401151 2005 eng d00aUnified derivations of measurement-based schemes for quantum computation0 aUnified derivations of measurementbased schemes for quantum comp c2005/3/170 v713 a We present unified, systematic derivations of schemes in the two known measurement-based models of quantum computation. The first model (introduced by Raussendorf and Briegel [Phys. Rev. Lett., 86, 5188 (2001)]) uses a fixed entangled state, adaptive measurements on single qubits, and feedforward of the measurement results. The second model (proposed by Nielsen [Phys. Lett. A, 308, 96 (2003)] and further simplified by Leung [Int. J. Quant. Inf., 2, 33 (2004)]) uses adaptive two-qubit measurements that can be applied to arbitrary pairs of qubits, and feedforward of the measurement results. The underlying principle of our derivations is a variant of teleportation introduced by Zhou, Leung, and Chuang [Phys. Rev. A, 62, 052316 (2000)]. Our derivations unify these two measurement-based models of quantum computation and provide significantly simpler schemes. 1 aChilds, Andrew, M.1 aLeung, Debbie, W.1 aNielsen, Michael, A. uhttp://arxiv.org/abs/quant-ph/0404132v201386nas 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/0405097v100715nas a2200145 4500008004100000245006300041210006300104260001500167490000700182520026200189100002300451700002600474700002500500856004400525 2003 eng d00aLower bounds on the complexity of simulating quantum gates0 aLower bounds on the complexity of simulating quantum gates c2003/11/180 v683 a We give a simple proof of a formula for the minimal time required to simulate a two-qubit unitary operation using a fixed two-qubit Hamiltonian together with fast local unitaries. We also note that a related lower bound holds for arbitrary n-qubit gates. 1 aChilds, Andrew, M.1 aHaselgrove, Henry, L.1 aNielsen, Michael, A. uhttp://arxiv.org/abs/quant-ph/0307190v101113nas a2200169 4500008004100000245006000041210006000101260001400161490000700175520059300182100002500775700002500800700002300825700002300848700002800871856004400899 2002 eng d00aUniversal simulation of Hamiltonian dynamics for qudits0 aUniversal simulation of Hamiltonian dynamics for qudits c2002/8/300 v663 a What interactions are sufficient to simulate arbitrary quantum dynamics in a composite quantum system? Dodd et al. (quant-ph/0106064) provided a partial solution to this problem in the form of an efficient algorithm to simulate any desired two-body Hamiltonian evolution using any fixed two-body entangling N-qubit Hamiltonian, and local unitaries. We extend this result to the case where the component systems have D dimensions. As a consequence we explain how universal quantum computation can be performed with any fixed two-body entangling N-qudit Hamiltonian, and local unitaries. 1 aNielsen, Michael, A.1 aBremner, Michael, J.1 aDodd, Jennifer, L.1 aChilds, Andrew, M.1 aDawson, Christopher, M. uhttp://arxiv.org/abs/quant-ph/0109064v2