TY - JOUR T1 - The maximum refractive index of an atomic crystal - from quantum optics to quantum chemistry Y1 - 2023 A1 - Francesco Andreoli A1 - Bennet Windt A1 - Stefano Grava A1 - Gian Marcello Andolina A1 - Michael J. Gullans A1 - Alexander A. High A1 - Darrick E. Chang AB -

All known optical materials have an index of refraction of order unity. Despite the tremendous implications that an ultrahigh index could have for optical technologies, little research has been done on why the refractive index of materials is universally small, and whether this observation is fundamental. Here, we investigate the index of an ordered arrangement of atoms, as a function of atomic density. At dilute densities, this problem falls into the realm of quantum optics, where atoms do not interact with one another except via the scattering of light. On the other hand, when the lattice constant becomes comparable to the Bohr radius, the electronic orbitals begin to overlap, giving rise to quantum chemistry. We present a minimal model that allows for a unifying theory of index spanning these two regimes. A key aspect is the treatment of multiple light scattering, which can be highly non-perturbative over a large density range, and which is the reason that conventional theories of the index break down. In the quantum optics regime, we show that ideal light-matter interactions can have a single-mode nature, allowing for a purely real refractive index that grows with density as (N/V)1/3. At the onset of quantum chemistry, we show how two physical mechanisms (excited electron tunneling dynamics and the buildup of electronic density-density correlations) can open up inelastic or spatial multi-mode light scattering processes, which ultimately reduce the index back to order unity while introducing absorption. Around the onset of chemistry, our theory predicts that ultrahigh index (n∼30), low-loss materials could in principle be allowed by the laws of nature. 

UR - https://arxiv.org/abs/2303.10998 ER - TY - JOUR T1 - Microwave signal processing using an analog quantum reservoir computer Y1 - 2023 A1 - Alen Senanian A1 - Sridhar Prabhu A1 - Vladimir Kremenetski A1 - Saswata Roy A1 - Yingkang Cao A1 - Jeremy Kline A1 - Tatsuhiro Onodera A1 - Logan G. Wright A1 - Xiaodi Wu A1 - Valla Fatemi A1 - Peter L. McMahon AB -

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

UR - https://arxiv.org/abs/2312.16166 ER - TY - JOUR T1 - Minimum-entanglement protocols for function estimation JF - Physical Review Research Y1 - 2023 A1 - Adam Ehrenberg A1 - Jacob Bringewatt A1 - Alexey V. Gorshkov AB -

We derive a family of optimal protocols, in the sense of saturating the quantum Cramér-Rao bound, for measuring a linear combination of d field amplitudes with quantum sensor networks, a key subprotocol of general quantum sensor network applications. We demonstrate how to select different protocols from this family under various constraints. Focusing primarily on entanglement-based constraints, we prove the surprising result that highly entangled states are not necessary to achieve optimality in many cases. Specifically, we prove necessary and sufficient conditions for the existence of optimal protocols using at most k-partite entanglement. We prove that the protocols which satisfy these conditions use the minimum amount of entanglement possible, even when given access to arbitrary controls and ancilla. Our protocols require some amount of time-dependent control, and we show that a related class of time-independent protocols fail to achieve optimal scaling for generic functions.

VL - 5 UR - https://arxiv.org/abs/2110.07613 U5 - 10.1103/physrevresearch.5.033228 ER - TY - JOUR T1 - Machine-assisted discovery of integrable symplectic mappings Y1 - 2022 A1 - Zolkin, Timofey A1 - Kharkov, Yaroslav A1 - Nagaitsev, Sergei KW - Accelerator Physics (physics.acc-ph) KW - Adaptation and Self-Organizing Systems (nlin.AO) KW - Exactly Solvable and Integrable Systems (nlin.SI) KW - FOS: Physical sciences AB -

We 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.

UR - https://arxiv.org/abs/2201.13133 U5 - 10.48550/ARXIV.2201.13133 ER - TY - JOUR T1 - Mana and thermalization: Probing the feasibility of near-Clifford Hamiltonian simulation JF - Physical Review B Y1 - 2022 A1 - Troy J. Sewell A1 - Christopher David White AB -

Quantum hydrodynamics is the emergent classical dynamics governing transport of conserved quantities in generic strongly-interacting quantum systems. Recent matrix product operator methods have made simulations of quantum hydrodynamics in 1+1d tractable, but they do not naturally generalize to 2+1d or higher, and they offer limited guidance as to the difficulty of simulations on quantum computers. Near-Clifford simulation algorithms are not limited to one dimension, and future error-corrected quantum computers will likely be bottlenecked by non-Clifford operations. We therefore investigate the non-Clifford resource requirements for simulation of quantum hydrodynamics using ``mana'', a resource theory of non-Clifford operations. For infinite-temperature starting states we find that the mana of subsystems quickly approaches zero, while for starting states with energy above some threshold the mana approaches a nonzero value. Surprisingly, in each case the finite-time mana is governed by the subsystem entropy, not the thermal state mana; we argue that this is because mana is a sensitive diagnostic of finite-time deviations from canonical typicality.

VL - 106 UR - https://arxiv.org/abs/2201.12367 U5 - 10.1103/physrevb.106.125130 ER - TY - JOUR T1 - Many-Body Quantum Teleportation via Operator Spreading in the Traversable Wormhole Protocol JF - Physical Review X Y1 - 2022 A1 - Thomas Schuster A1 - Bryce Kobrin A1 - Ping Gao A1 - Iris Cong A1 - Emil T. Khabiboulline A1 - Norbert M. Linke A1 - Mikhail D. Lukin A1 - Christopher Monroe A1 - Beni Yoshida A1 - Norman Y. Yao AB -

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

VL - 12 UR - https://arxiv.org/abs/2102.00010 U5 - 10.1103/physrevx.12.031013 ER - TY - JOUR T1 - The Mathematics of Quantum Coin-Flipping JF - Notices of the American Mathematical Society Y1 - 2022 A1 - Carl Miller VL - 69 U4 - 1908-1917 UR - https://www.ams.org/notices/202211/rnoti-p1908.pdf CP - 11 J1 - Notices Amer. Math. Soc. U5 - https://doi.org/10.1090/noti2575 ER - TY - JOUR T1 - Modular commutator in gapped quantum many-body systems JF - Physical Review B Y1 - 2022 A1 - Isaac H. Kim A1 - Bowen Shi A1 - Kohtaro Kato A1 - Victor V. Albert AB -

In arXiv:2110.06932, we argued that the chiral central charge -- a topologically protected quantity characterizing the edge theory of a gapped (2+1)-dimensional system -- can be extracted from the bulk by using an order parameter called the modular commutator. In this paper, we reveal general properties of the modular commutator and strengthen its relationship with the chiral central charge. First, we identify connections between the modular commutator and conditional mutual information, time reversal, and modular flow. Second, we prove, within the framework of the entanglement bootstrap program, that two topologically ordered media connected by a gapped domain wall must have the same modular commutator in their respective bulk. Third, we numerically calculate the value of the modular commutator for a bosonic lattice Laughlin state for finite sizes and extrapolate to the infinite-volume limit. The result of this extrapolation is consistent with the proposed formula up to an error of about 0.7%.

VL - 106 UR - https://arxiv.org/abs/2110.10400 U5 - 10.1103/physrevb.106.075147 ER - TY - JOUR T1 - Monitoring-induced Entanglement Entropy and Sampling Complexity Y1 - 2022 A1 - Van Regemortel, Mathias A1 - Shtanko, Oles A1 - García-Pintos, Luis Pedro A1 - Deshpande, Abhinav A1 - Dehghani, Hossein A1 - Alexey V. Gorshkov A1 - Hafezi, Mohammad KW - FOS: Physical sciences KW - Quantum Physics (quant-ph) AB -

The dynamics of open quantum systems is generally described by a master equation, which describes the loss of information into the environment. By using a simple model of uncoupled emitters, we illustrate how the recovery of this information depends on the monitoring scheme applied to register the decay clicks. The dissipative dynamics, in this case, is described by pure-state stochastic trajectories and we examine different unravelings of the same master equation. More precisely, we demonstrate how registering the sequence of clicks from spontaneously emitted photons through a linear optical interferometer induces entanglement in the trajectory states. Since this model consists of an array of single-photon emitters, we show a direct equivalence with Fock-state boson sampling and link the hardness of sampling the outcomes of the quantum jumps with the scaling of trajectory entanglement.

UR - https://arxiv.org/abs/2201.12672 U5 - 10.48550/ARXIV.2201.12672 ER - TY - JOUR T1 - Multi-Angle QAOA Does Not Always Need All Its Angles Y1 - 2022 A1 - Shi, Kaiyan A1 - Herrman, Rebekah A1 - Shaydulin, Ruslan A1 - Chakrabarti, Shouvanik A1 - Pistoia, Marco A1 - Larson, Jeffrey KW - FOS: Physical sciences KW - Quantum Physics (quant-ph) AB -

Introducing additional tunable parameters to quantum circuits is a powerful way of improving performance without increasing hardware requirements. A recently introduced multi-angle extension of the quantum approximate optimization algorithm (ma-QAOA) significantly improves the solution from QAOA by allowing the parameters for each term in the Hamiltonian to vary independently. However, prior results suggest that there is considerable redundancy in parameters, the removal of which would reduce the cost of parameter optimization. In this work, we show numerically that problem symmetries can be used to reduce the number of parameters used by ma-QAOA without decreasing the solution quality. We study MaxCut on all 7,565 connected, non-isomorphic 8-node graphs with a non-trivial symmetry group and show numerically that in 67.4\% of these graphs, symmetry can be used to reduce the number of parameters with no decrease in the objective, with the average ratio of parameters reduced by 28.1\%. Moreover, we show that in 35.9\% of the graphs this can be achieved by simply using the largest symmetry. For the graphs where reducing the number of parameters leads to a decrease in the objective, the largest symmetry can be used to reduce the parameter count by 37.1\% at the cost of only a 6.1\% decrease in the objective.

UR - https://arxiv.org/abs/2209.11839 U5 - 10.48550/ARXIV.2209.11839 ER - TY - JOUR T1 - Machine learning outperforms thermodynamics in measuring how well a many-body system learns a drive JF - Scientific Reports Y1 - 2021 A1 - Zhong, Weishun A1 - Gold, Jacob M. A1 - Marzen, Sarah A1 - England, Jeremy L. A1 - Nicole Yunger Halpern AB -

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

VL - 11 UR - https://arxiv.org/abs/2004.03604 U5 - https://doi.org/10.1038/s41598-021-88311-7 ER - TY - JOUR T1 - Machine-learning enhanced dark soliton detection in Bose-Einstein condensates JF - Mach. Learn.: Sci. Technol. Y1 - 2021 A1 - Shangjie Guo A1 - Amilson R. Fritsch A1 - Craig Greenberg A1 - I. B. Spielman A1 - Justyna P. Zwolak AB -

Most data in cold-atom experiments comes from images, the analysis of which is limited by our preconceptions of the patterns that could be present in the data. We focus on the well-defined case of detecting dark solitons -- appearing as local density depletions in a BEC -- using a methodology that is extensible to the general task of pattern recognition in images of cold atoms. Studying soliton dynamics over a wide range of parameters requires the analysis of large datasets, making the existing human-inspection-based methodology a significant bottleneck. Here we describe an automated classification and positioning system for identifying localized excitations in atomic Bose-Einstein condensates (BECs) utilizing deep convolutional neural networks to eliminate the need for human image examination. Furthermore, we openly publish our labeled dataset of dark solitons, the first of its kind, for further machine learning research.

VL - 2 U4 - 035020 UR - https://arxiv.org/abs/2101.05404 U5 - https://doi.org/10.1088/2632-2153/abed1e ER - TY - JOUR T1 - Magic State Distillation from Entangled States Y1 - 2021 A1 - Ning Bao A1 - ChunJun Cao A1 - Vincent Paul Su AB -

Magic can be distributed non-locally in many-body entangled states, such as the low energy states of condensed matter systems. Using the Bravyi-Kitaev magic state distillation protocol, we find that non-local magic is distillable and can improve the distillation outcome. We analyze a few explicit examples and show that spin squeezing can be used to convert non-distillable states into distillable ones.
Our analysis also suggests that the conventional product input states assumed by magic distillation protocols are extremely atypical among general states with distillable magic. It further justifies the need for studying a diverse range of entangled inputs that yield magic states with high probability.

UR - https://arxiv.org/abs/2106.12591 ER - TY - JOUR T1 - Maximum Refractive Index of an Atomic Medium JF - Physical Review X Y1 - 2021 A1 - Andreoli, Francesco A1 - Michael Gullans A1 - High, Alexander A. A1 - Browaeys, Antoine A1 - Chang, Darrick E. AB -

It is interesting to observe that all optical materials with a positive refractive index have a value of index that is of order unity. Surprisingly, though, a deep understanding of the mechanisms that lead to this universal behavior seems to be lacking. Moreover, this observation is difficult to reconcile with the fact that a single, isolated atom is known to have a giant optical response, as characterized by a resonant scattering cross section that far exceeds its physical size. Here, we theoretically and numerically investigate the evolution of the optical properties of an ensemble of ideal atoms as a function of density, starting from the dilute gas limit, including the effects of multiple scattering and near-field interactions. Interestingly, despite the giant response of an isolated atom, we find that the maximum index does not indefinitely grow with increasing density, but rather reaches a limiting value n≈1.7. We propose an explanation based upon strong-disorder renormalization group theory, in which the near-field interaction combined with random atomic positions results in an inhomogeneous broadening of atomic resonance frequencies. This mechanism ensures that regardless of the physical atomic density, light at any given frequency only interacts with at most a few near-resonant atoms per cubic wavelength, thus limiting the maximum index attainable. Our work is a promising first step to understand the limits of refractive index from a bottom-up, atomic physics perspective, and also introduces renormalization group as a powerful tool to understand the generally complex problem of multiple scattering of light overall.

VL - 11 UR - https://arxiv.org/abs/2006.01680 CP - 1 J1 - Phys. Rev. X U5 - 10.1103/PhysRevX.11.011026 ER - TY - JOUR T1 - The membership problem for constant-sized quantum correlations is undecidable Y1 - 2021 A1 - Honghao Fu A1 - Carl Miller A1 - William Slofstra AB -

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

UR - https://arxiv.org/abs/2101.11087 ER - TY - JOUR T1 - Meta Hamiltonian Learning Y1 - 2021 A1 - Przemyslaw Bienias A1 - Alireza Seif A1 - Mohammad Hafezi AB -

Efficient characterization of quantum devices is a significant challenge critical for the development of large scale quantum computers. We consider an experimentally motivated situation, in which we have a decent estimate of the Hamiltonian, and its parameters need to be characterized and fine-tuned frequently to combat drifting experimental variables. We use a machine learning technique known as meta-learning to learn a more efficient optimizer for this task. We consider training with the nearest-neighbor Ising model and study the trained model's generalizability to other Hamiltonian models and larger system sizes. We observe that the meta-optimizer outperforms other optimization methods in average loss over test samples. This advantage follows from the meta-optimizer being less likely to get stuck in local minima, which highly skews the distribution of the final loss of the other optimizers. In general, meta-learning decreases the number of calls to the experiment and reduces the needed classical computational resources.

UR - https://arxiv.org/abs/2104.04453 ER - TY - JOUR T1 - Machine learning the thermodynamic arrow of time JF - Nat. Phys. Y1 - 2020 A1 - Alireza Seif A1 - Mohammad Hafezi A1 - Christopher Jarzynski AB -

The mechanism by which thermodynamics sets the direction of time's arrow has long fascinated scientists. Here, we show that a machine learning algorithm can learn to discern the direction of time's arrow when provided with a system's microscopic trajectory as input. The performance of our algorithm matches fundamental bounds predicted by nonequilibrium statistical mechanics. Examination of the algorithm's decision-making process reveals that it discovers the underlying thermodynamic mechanism and the relevant physical observables. Our results indicate that machine learning techniques can be used to study systems out of equilibrium, and ultimately to uncover physical principles.

U4 - 1-9 UR - https://arxiv.org/abs/1909.12380 U5 - https://doi.org/10.1038/s41567-020-1018-2 ER - TY - JOUR T1 - Many-Body Dephasing in a Trapped-Ion Quantum Simulator JF - Phys. Rev. Lett. Y1 - 2020 A1 - Harvey B. Kaplan A1 - Lingzhen Guo A1 - Wen Lin Tan A1 - Arinjoy De A1 - Florian Marquardt A1 - Guido Pagano A1 - Christopher Monroe AB -

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

VL - 125 UR - https://arxiv.org/abs/2001.02477 CP - 120605 U5 - https://doi.org/10.1103/PhysRevLett.125.120605 ER - TY - JOUR T1 - Mechanical Quantum Sensing in the Search for Dark Matter Y1 - 2020 A1 - D. Carney A1 - G. Krnjaic A1 - D. C. Moore A1 - C. A. Regal A1 - G. Afek A1 - S. Bhave A1 - B. Brubaker A1 - T. Corbitt A1 - J. Cripe A1 - N. Crisosto A1 - A.Geraci A1 - S. Ghosh A1 - J. G. E. Harris A1 - A. Hook A1 - E. W. Kolb A1 - J. Kunjummen A1 - R. F. Lang A1 - T. Li A1 - T. Lin A1 - Z. Liu A1 - J. Lykken A1 - L. Magrini A1 - J. Manley A1 - N. Matsumoto A1 - A. Monte A1 - F. Monteiro A1 - T. Purdy A1 - C. J. Riedel A1 - R. Singh A1 - S. Singh A1 - K. Sinha A1 - J. M. Taylor A1 - J. Qin A1 - D. J. Wilson A1 - Y. Zhao AB -

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

UR - https://arxiv.org/abs/2008.06074 ER - TY - JOUR T1 - Minimal model for fast scrambling JF - Phys. Rev. Lett. Y1 - 2020 A1 - Ron Belyansky A1 - Przemyslaw Bienias A1 - Yaroslav A. Kharkov A1 - Alexey V. Gorshkov A1 - Brian Swingle AB -

We study quantum information scrambling in spin models with both long-range all-to-all and short-range interactions. We argue that a simple global, spatially homogeneous interaction together with local chaotic dynamics is sufficient to give rise to fast scrambling, which describes the spread of quantum information over the entire system in a time that is logarithmic in the system size. This is illustrated in two exactly solvable models: (1) a random circuit with Haar random local unitaries and a global interaction and (2) a classical model of globally coupled non-linear oscillators. We use exact numerics to provide further evidence by studying the time evolution of an out-of-time-order correlator and entanglement entropy in spin chains of intermediate sizes. Our results can be verified with state-of-the-art quantum simulators.

VL - 125 UR - https://arxiv.org/abs/2005.05362 CP - 130601 U5 - https://doi.org/10.1103/PhysRevLett.125.130601 ER - TY - JOUR T1 - More of the Bulk from Extremal Area Variations JF - Classical and Quantum Gravity Y1 - 2020 A1 - Ning Bao A1 - ChunJun Cao A1 - Sebastian Fischetti A1 - Jason Pollack A1 - Yibo Zhong AB -

It was shown recently, building on work of Alexakis, Balehowksy, and Nachman that the geometry of (some portion of) a manifold with boundary is uniquely fixed by the areas of a foliation of two-dimensional disk-shaped surfaces anchored to the boundary. In the context of AdS/CFT, this implies that (a portion of) a four-dimensional bulk geometry can be fixed uniquely from the entanglement entropies of disk-shaped boundary regions, subject to several constraints. In this Note, we loosen some of these constraints, in particular allowing for the bulk foliation of extremal surfaces to be local and removing the constraint of disk topology; these generalizations ensure uniqueness of more of the deep bulk geometry by allowing for e.g. surfaces anchored on disconnected asymptotic boundaries, or HRT surfaces past a phase transition. We also explore in more depth the generality of the local foliation requirement, showing that even in a highly dynamical geometry like AdS-Vaidya it is satisfied.

VL - 38 U4 - 047001 UR - https://arxiv.org/abs/2009.07850 CP - 4 U5 - https://iopscience.iop.org/article/10.1088/1361-6382/abcfd0/pdf ER - TY - JOUR T1 - Momentum-space entanglement after a quench in one-dimensional disordered fermionic systems Y1 - 2019 A1 - Rex Lundgren A1 - Fangli Liu A1 - Pontus Laurell A1 - Gregory A. Fiete AB -

We numerically investigate the momentum-space entanglement entropy and entanglement spectrum of the random-dimer model and its generalizations, which circumvent Anderson localization, after a quench in the Hamiltonian parameters. The type of dynamics that occurs depends on whether or not the Fermi level of the initial state is near the energy of the delocalized states present in these models. If the Fermi level of the initial state is near the energy of the delocalized states, we observe an interesting slow logarithmic-like growth of the momentum-space entanglement entropy followed by an eventual saturation. Otherwise, the momentum-space entanglement entropy is found to rapidly saturate. We also find that the momentum-space entanglement spectrum reveals the presence of delocalized states in these models for long times after the quench and the many-body entanglement gap decays logarithmically in time when the Fermi level is near the energy of the delocalized states.

UR - https://arxiv.org/abs/1909.05140 ER - TY - JOUR T1 - Machine learning assisted readout of trapped-ion qubits JF - J. Phys. B: At. Mol. Opt. Phys. Y1 - 2018 A1 - Alireza Seif A1 - Kevin A. Landsman A1 - Norbert M. Linke A1 - Caroline Figgatt A1 - C. Monroe A1 - Mohammad Hafezi AB -

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

VL - 51 UR - https://arxiv.org/abs/1804.07718 U5 - https://doi.org/10.1088/1361-6455/aad62b ER - TY - JOUR T1 - Mathematical methods for resource-based type theories Y1 - 2018 A1 - Aarthi Sundaram A1 - Brad Lackey AB -

With the wide range of quantum programming languages on offer now, efficient program verification and type checking for these languages presents a challenge -- especially when classical debugging techniques may affect the states in a quantum program. In this work, we make progress towards a program verification approach using the formalism of operational quantum mechanics and resource theories. We present a logical framework that captures two mathematical approaches to resource theory based on monoids (algebraic) and monoidal categories (categorical). We develop the syntax of this framework as an intuitionistic sequent calculus, and prove soundness and completeness of an algebraic and categorical semantics that recover these approaches. We also provide a cut-elimination theorem, normal form, and analogue of Lambek's lifting theorem for polynomial systems over the logics. Using these approaches along with the Curry-Howard-Lambek correspondence for programs, proofs and categories, this work lays the mathematical groundwork for a type checker for some resource theory based frameworks, with the possibility of extending it other quantum programming languages.

UR - https://arxiv.org/abs/1812.08726 ER - TY - JOUR T1 - Measurement Contextuality and Planck's Constant JF - New Journal of Physics Y1 - 2018 A1 - Lucas Kocia A1 - Peter Love AB -

Contextuality is a necessary resource for universal quantum computation and non-contextual quantum mechanics can be simulated efficiently by classical computers in many cases. Orders of Planck's constant, ℏ, can also be used to characterize the classical-quantum divide by expanding quantities of interest in powers of ℏ---all orders higher than ℏ0 can be interpreted as quantum corrections to the order ℏ0 term. We show that contextual measurements in finite-dimensional systems have formulations within the Wigner-Weyl-Moyal (WWM) formalism that require higher than order ℏ0 terms to be included in order to violate the classical bounds on their expectation values. As a result, we show that contextuality as a resource is equivalent to orders of ℏ as a resource within the WWM formalism. This explains why qubits can only exhibit state-independent contextuality under Pauli observables as in the Peres-Mermin square while odd-dimensional qudits can also exhibit state-dependent contextuality. In particular, we find that qubit Pauli observables lack an order ℏ0 contribution in their Weyl symbol and so exhibit contextuality regardless of the state being measured. On the other hand, odd-dimensional qudit observables generally possess non-zero order ℏ0 terms, and higher, in their WWM formulation, and so exhibit contextuality depending on the state measured: odd-dimensional qudit states that exhibit measurement contextuality have an order ℏ1 contribution that allows for the violation of classical bounds while states that do not exhibit measurement contextuality have insufficiently large order ℏ1 contributions.

VL - 20 U4 - 073020 UR - https://arxiv.org/abs/1711.08066 CP - 7 U5 - https://doi.org/10.1088/1367-2630/aacef2 ER - TY - JOUR T1 - More is Less: Perfectly Secure Oblivious Algorithms in the Multi-Server Setting Y1 - 2018 A1 - Hubert Chan A1 - Jonathan Katz A1 - Kartik Nayak A1 - Antigoni Polychroniadou A1 - Elaine Shi AB -

The 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. 

UR - https://arxiv.org/abs/1809.00825 ER - TY - JOUR T1 - Morphisms in categories of nonlocal games Y1 - 2018 A1 - Brad Lackey A1 - Nishant Rodrigues AB -

Synchronous correlations provide a class of nonlocal games that behave like functions between finite sets. In this work we examine categories whose morphisms are games with synchronous classical, quantum, or general nonsignaling correlations. In particular, we characterize when morphisms in these categories are monic, epic, sections, or retractions.

UR - https://arxiv.org/abs/1810.10074 ER - TY - JOUR T1 - Multiparty quantum data hiding with enhanced security and remote deletion Y1 - 2018 A1 - Xingyao Wu A1 - Jianxin Chen AB -

One of the applications of quantum technology is to use quantum states and measurements to communicate which offers more reliable security promises. Quantum data hiding, which gives the source party the ability of sharing data among multiple receivers and revealing it at a later time depending on his/her will, is one of the promising information sharing schemes which may address practical security issues. In this work, we propose a novel quantum data hiding protocol. By concatenating different subprotocols which apply to rather symmetric hiding scenarios, we cover a variety of more general hiding scenarios. We provide the general requirements for constructing such protocols and give explicit examples of encoding states for five parties. We also proved the security of the protocol in sense that the achievable information by unauthorized operations asymptotically goes to zero. In addition, due to the capability of the sender to manipulate his/her subsystem, the sender is able to abort the protocol remotely at any time before he/she reveals the information.

U4 - 5 UR - https://arxiv.org/abs/1804.01982 ER - TY - JOUR T1 - Machine Learning techniques for state recognition and auto-tuning in quantum dots Y1 - 2017 A1 - Sandesh S. Kalantre A1 - Justyna P. Zwolak A1 - Stephen Ragole A1 - Xingyao Wu A1 - Neil M. Zimmerman A1 - M. D. Stewart A1 - J. M. Taylor AB -

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

UR - https://arxiv.org/abs/1712.04914 ER - TY - JOUR T1 - Modulus of continuity eigenvalue bounds for homogeneous graphs and convex subgraphs with applications to quantum Hamiltonians JF - Journal of Mathematical Analysis and Applications Y1 - 2017 A1 - Michael Jarret A1 - Stephen P. Jordan AB -

We adapt modulus of continuity estimates to the study of spectra of combinatorial graph Laplacians, as well as the Dirichlet spectra of certain weighted Laplacians. The latter case is equivalent to stoquastic Hamiltonians and is of current interest in both condensed matter physics and quantum computing. In particular, we introduce a new technique which bounds the spectral gap of such Laplacians (Hamiltonians) by studying the limiting behavior of the oscillations of their eigenvectors when introduced into the heat equation. Our approach is based on recent advances in the PDE literature, which include a proof of the fundamental gap theorem by Andrews and Clutterbuck.

VL - 452 U4 - 1269-1290 UR - http://www.sciencedirect.com/science/article/pii/S0022247X1730272X CP - 2 U5 - 10.1016/j.jmaa.2017.03.030 ER - TY - JOUR T1 - Multicritical behavior in dissipative Ising models JF - Physical Review A Y1 - 2017 A1 - Vincent R. Overbeck A1 - Mohammad F. Maghrebi A1 - Alexey V. Gorshkov A1 - Hendrik Weimer AB -

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

VL - 95 U4 - 042133 UR - https://journals.aps.org/pra/abstract/10.1103/PhysRevA.95.042133 U5 - doi.org/10.1103/PhysRevA.95.042133 ER - TY - JOUR T1 - Many-body decoherence dynamics and optimised operation of a single-photon switch JF - New Journal of Physics Y1 - 2016 A1 - Callum R. Murray A1 - Alexey V. Gorshkov A1 - Thomas Pohl AB -

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

VL - 18 U4 - 092001 UR - http://iopscience.iop.org/article/10.1088/1367-2630/18/9/092001 U5 - 10.1088/1367-2630/18/9/092001 ER - TY - JOUR T1 - Many-body localization in a quantum simulator with programmable random disorder JF - Nature Physics Y1 - 2016 A1 - Jacob Smith A1 - Aaron Lee A1 - Philip Richerme A1 - Brian Neyenhuis A1 - Paul W. Hess A1 - Philipp Hauke A1 - Markus Heyl A1 - David A. Huse A1 - Christopher Monroe AB -

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

UR - http://arxiv.org/abs/1508.07026v1 U5 - 10.1038/nphys3783 ER - TY - JOUR T1 - Mapping constrained optimization problems to quantum annealing with application to fault diagnosis Y1 - 2016 A1 - Bian, Zhengbing A1 - Chudak, Fabian A1 - Israel, Robert A1 - Lackey, Brad A1 - Macready, William G A1 - Roy, Aidan AB - Current quantum annealing (QA) hardware suffers from practical limitations such as finite temperature, sparse connectivity, small qubit numbers, and control error. We propose new algorithms for mapping boolean constraint satisfaction problems (CSPs) onto QA hardware mitigating these limitations. In particular we develop a new embedding algorithm for mapping a CSP onto a hardware Ising model with a fixed sparse set of interactions, and propose two new decomposition algorithms for solving problems too large to map directly into hardware. The mapping technique is locally-structured, as hardware compatible Ising models are generated for each problem constraint, and variables appearing in different constraints are chained together using ferromagnetic couplings. In contrast, global embedding techniques generate a hardware independent Ising model for all the constraints, and then use a minor-embedding algorithm to generate a hardware compatible Ising model. We give an example of a class of CSPs for which the scaling performance of D-Wave's QA hardware using the local mapping technique is significantly better than global embedding. We validate the approach by applying D-Wave's hardware to circuit-based fault-diagnosis. For circuits that embed directly, we find that the hardware is typically able to find all solutions from a min-fault diagnosis set of size N using 1000N samples, using an annealing rate that is 25 times faster than a leading SAT-based sampling method. Further, we apply decomposition algorithms to find min-cardinality faults for circuits that are up to 5 times larger than can be solved directly on current hardware. UR - http://arxiv.org/abs/1603.03111 ER - TY - JOUR T1 - Mapping contrained optimization problems to quantum annealing with application to fault diagnosis JF - Frontiers in ICT Y1 - 2016 A1 - Bian, Zhengbing A1 - Chudak, Fabian A1 - Robert Brian Israel A1 - Brad Lackey A1 - Macready, William G A1 - Aiden Roy AB -

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

VL - 3 U4 - 14 UR - http://journal.frontiersin.org/article/10.3389/fict.2016.00014/full ER - TY - JOUR T1 - Measurement Protocol for the Entanglement Spectrum of Cold Atoms JF - Phys. Rev. X Y1 - 2016 A1 - Hannes Pichler A1 - Guanyu Zhu A1 - Alireza Seif A1 - Peter Zoller A1 - Mohammad Hafezi AB -

Entanglement, and, in particular the entanglement spectrum, plays a major role in characterizing many-body quantum systems. While there has been a surge of theoretical works on the subject, no experimental measurement has been performed to date because of the lack of an implementable measurement scheme. Here, we propose a measurement protocol to access the entanglement spectrum of many-body states in experiments with cold atoms in optical lattices. Our scheme effectively performs a Ramsey spectroscopy of the entanglement Hamiltonian and is based on the ability to produce several copies of the state under investigation together with the possibility to perform a global swap gate between two copies conditioned on the state of an auxiliary qubit. We show how the required conditional swap gate can be implemented with cold atoms, either by using Rydberg interactions or coupling the atoms to a cavity mode. We illustrate these ideas on a simple (extended) Bose-Hubbard model where such a measurement protocol reveals topological features of the Haldane phase. 

VL - 6(4) UR - https://arxiv.org/abs/1605.08624 CP - 041033 U5 - https://doi.org/10.1103/PhysRevX.6.041033 ER - TY - JOUR T1 - Multiple scattering dynamics of fermions at an isolated p-wave resonance JF - Nature Communications Y1 - 2016 A1 - Ryan Thomas A1 - Kris O. Roberts A1 - Eite Tiesinga A1 - Andrew C.J. Wade A1 - P. Blair Blakie A1 - Amita B. Deb A1 - Niels Kjærgaard AB -

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

VL - 7 U4 - 12069 UR - http://www.nature.com/articles/ncomms12069 U5 - 10.1038/ncomms12069 ER - TY - JOUR T1 - The Measurement Problem from the Perspective of an Information Theoretic Interpretation of Quantum Mechanics JF - Entropy Y1 - 2015 A1 - Jeffrey Bub AB - The aim of this paper is to consider the consequences of an information-theoretic interpretation of quantum mechanics for the measurement problem. The motivating idea of the interpretation is that the relation between quantum mechanics and the structure of information is analogous to the relation between special relativity and the structure of space-time. Insofar as quantum mechanics deals with a class of probabilistic correlations that includes correlations structurally different from classical correlations, the theory is about the structure of information: the possibilities for representing, manipulating, and communicating information in a genuinely indeterministic quantum world in which measurement outcomes are intrinsically random are different than we thought. Part of the measurement problem is deflated as a pseudo-problem on this view, and the theory has the resources to deal with the remaining part, given certain idealizations in the treatment of macrosystems. VL - 17 U4 - 7374-7386 UR - http://www.mdpi.com/1099-4300/17/11/7374 CP - 11 U5 - 10.3390/e17117374 ER - TY - JOUR T1 - The Minimum Size of Unextendible Product Bases in the Bipartite Case (and Some Multipartite Cases) JF - Communications in Mathematical Physics Y1 - 2015 A1 - Jianxin Chen A1 - Nathaniel Johnston AB - A long-standing open question asks for the minimum number of vectors needed to form an unextendible product basis in a given bipartite or multipartite Hilbert space. A partial solution was found by Alon and Lovasz in 2001, but since then only a few other cases have been solved. We solve all remaining bipartite cases, as well as a large family of multipartite cases. VL - 333 U4 - 351 - 365 UR - http://arxiv.org/abs/1301.1406v1 CP - 1 J1 - Commun. Math. Phys. U5 - 10.1007/s00220-014-2186-7 ER - TY - JOUR T1 - Momentum switches JF - Quantum Information and Computation Y1 - 2015 A1 - Andrew M. Childs A1 - David Gosset A1 - Daniel Nagaj A1 - Mouktik Raha A1 - Zak Webb AB - 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. VL - 15 U4 - 601-621 UR - http://arxiv.org/abs/1406.4510v1 CP - 7-8 J1 - Quantum Information and Computation 15 ER - TY - JOUR T1 - Many-body dynamics of dipolar molecules in an optical lattice JF - Physical Review Letters Y1 - 2014 A1 - Kaden R. A. Hazzard A1 - Bryce Gadway A1 - Michael Foss-Feig A1 - Bo Yan A1 - Steven A. Moses A1 - Jacob P. Covey A1 - Norman Y. Yao A1 - Mikhail D. Lukin A1 - Jun Ye A1 - Deborah S. Jin A1 - Ana Maria Rey AB - Understanding the many-body dynamics of isolated quantum systems is one of the central challenges in modern physics. To this end, the direct experimental realization of strongly correlated quantum systems allows one to gain insights into the emergence of complex phenomena. Such insights enable the development of theoretical tools that broaden our understanding. Here, we theoretically model and experimentally probe with Ramsey spectroscopy the quantum dynamics of disordered, dipolar-interacting, ultracold molecules in a partially filled optical lattice. We report the capability to control the dipolar interaction strength, and we demonstrate that the many-body dynamics extends well beyond a nearest-neighbor or mean-field picture, and cannot be quantitatively described using previously available theoretical tools. We develop a novel cluster expansion technique and demonstrate that our theoretical method accurately captures the measured dependence of the spin dynamics on molecule number and on the dipolar interaction strength. In the spirit of quantum simulation, this agreement simultaneously benchmarks the new theoretical method and verifies our microscopic understanding of the experiment. Our findings pave the way for numerous applications in quantum information science, metrology, and condensed matter physics. VL - 113 UR - http://arxiv.org/abs/1402.2354v1 CP - 19 J1 - Phys. Rev. Lett. U5 - 10.1103/PhysRevLett.113.195302 ER - TY - JOUR T1 - Multilingual Summarization: Dimensionality Reduction and a Step Towards Optimal Term Coverage JF - MultiLing (Workshop on Multilingual Multi-document Summarization) Y1 - 2013 A1 - John M. Conroy A1 - Sashka T. Davis A1 - Jeff Kubina A1 - Yi-Kai Liu A1 - Dianne P. O'Leary A1 - Judith D. Schlesinger AB - In this paper we present three term weighting approaches for multi-lingual document summarization and give results on the DUC 2002 data as well as on the 2013 Multilingual Wikipedia feature articles data set. We introduce a new intervalbounded nonnegative matrix factorization. We use this new method, latent semantic analysis (LSA), and latent Dirichlet allocation (LDA) to give three term-weighting methods for multi-document multi-lingual summarization. Results on DUC and TAC data, as well as on the MultiLing 2013 data, demonstrate that these methods are very promising, since they achieve oracle coverage scores in the range of humans for 6 of the 10 test languages. Finally, we present three term weighting approaches for the MultiLing13 single document summarization task on the Wikipedia featured articles. Our submissions signifi- cantly outperformed the baseline in 19 out of 41 languages. U4 - 55-63 UR - http://aclweb.org/anthology/W/W13/W13-3108.pdf ER - TY - JOUR T1 - Minimum Entangling Power is Close to Its Maximum Y1 - 2012 A1 - Jianxin Chen A1 - Zhengfeng Ji A1 - David W Kribs A1 - Bei Zeng AB - Given a quantum gate $U$ acting on a bipartite quantum system, its maximum (average, minimum) entangling power is the maximum (average, minimum) entanglement generation with respect to certain entanglement measure when the inputs are restricted to be product states. In this paper, we mainly focus on the 'weakest' one, i.e., the minimum entangling power, among all these entangling powers. We show that, by choosing von Neumann entropy of reduced density operator or Schmidt rank as entanglement measure, even the 'weakest' entangling power is generically very close to its maximal possible entanglement generation. In other words, maximum, average and minimum entangling powers are generically close. We then study minimum entangling power with respect to other Lipschitiz-continuous entanglement measures and generalize our results to multipartite quantum systems. As a straightforward application, a random quantum gate will almost surely be an intrinsically fault-tolerant entangling device that will always transform every low-entangled state to near-maximally entangled state. UR - http://arxiv.org/abs/1210.1296v1 ER - TY - JOUR T1 - Matrix pencils and entanglement classification JF - Journal of Mathematical Physics Y1 - 2010 A1 - Chitambar, Eric A1 - Carl Miller A1 - Shi, Yaoyun AB -

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

VL - 51 U4 - 072205 UR - http://scitation.aip.org/content/aip/journal/jmp/51/7/10.1063/1.3459069 CP - 7 J1 - J. Math. Phys. U5 - 10.1063/1.3459069 ER - TY - JOUR T1 - Many-Body Treatment of the Collisional Frequency Shift in Fermionic Atoms JF - Phys. Rev. Lett. Y1 - 2009 A1 - Rey, A M A1 - Alexey V. Gorshkov A1 - Rubbo, C VL - 103 U4 - 260402 UR - http://link.aps.org/abstract/PRL/v103/e260402/ ER - TY - JOUR T1 - Multi-channel modelling of the formation of vibrationally cold polar KRb molecules JF - New Journal of Physics Y1 - 2009 A1 - Svetlana Kotochigova A1 - Eite Tiesinga A1 - Paul S. Julienne AB - We describe the theoretical advances that influenced the experimental creation of vibrationally and translationally cold polar $^{40}$K$^{87}$Rb molecules \cite{nphys08,science08}. Cold molecules were created from very-weakly bound molecules formed by magnetic field sweeps near a Feshbach resonance in collisions of ultra-cold $^{40}$K and $^{87}$Rb atoms. Our analysis include the multi-channel bound-state calculations of the hyperfine and Zeeman mixed X$^1\Sigma^+$ and a$^3\Sigma^+$ vibrational levels. We find excellent agreement with the hyperfine structure observed in experimental data. In addition, we studied the spin-orbit mixing in the intermediate state of the Raman transition. This allowed us to investigate its effect on the vibrationally-averaged transition dipole moment to the lowest ro-vibrational level of the X$^1\Sigma^+$ state. Finally, we obtained an estimate of the polarizability of the initial and final ro-vibrational states of the Raman transition near frequencies relevant for optical trapping of the molecules. VL - 11 U4 - 055043 UR - http://arxiv.org/abs/0901.1486v1 CP - 5 J1 - New J. Phys. U5 - 10.1088/1367-2630/11/5/055043 ER - TY - JOUR T1 - Multilevel effects in the Rabi oscillations of a Josephson phase qubit JF - Physical Review B Y1 - 2008 A1 - S. K. Dutta A1 - Frederick W. Strauch A1 - R. M. Lewis A1 - Kaushik Mitra A1 - Hanhee Paik A1 - T. A. Palomaki A1 - Eite Tiesinga A1 - J. R. Anderson A1 - Alex J. Dragt A1 - C. J. Lobb A1 - F. C. Wellstood AB - We present Rabi oscillation measurements of a Nb/AlOx/Nb dc superconducting quantum interference device (SQUID) phase qubit with a 100 um^2 area junction acquired over a range of microwave drive power and frequency detuning. Given the slightly anharmonic level structure of the device, several excited states play an important role in the qubit dynamics, particularly at high power. To investigate the effects of these levels, multiphoton Rabi oscillations were monitored by measuring the tunneling escape rate of the device to the voltage state, which is particularly sensitive to excited state population. We compare the observed oscillation frequencies with a simplified model constructed from the full phase qubit Hamiltonian and also compare time-dependent escape rate measurements with a more complete density-matrix simulation. Good quantitative agreement is found between the data and simulations, allowing us to identify a shift in resonance (analogous to the ac Stark effect), a suppression of the Rabi frequency, and leakage to the higher excited states. VL - 78 UR - http://arxiv.org/abs/0806.4711v2 CP - 10 J1 - Phys. Rev. B U5 - 10.1103/PhysRevB.78.104510 ER - TY - JOUR T1 - Multi-photon Entanglement: From Quantum Curiosity to Quantum Computing and Quantum Repeaters JF - Proc. SPIE Y1 - 2007 A1 - Walther, P A1 - Eisaman, M D A1 - Nemiroski, A A1 - Alexey V. Gorshkov A1 - Zibrov, A S A1 - Zeilinger, A A1 - Lukin, M D VL - 6664 U4 - 66640G UR - http://spiedigitallibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PSISDG00666400000166640G000001&idtype=cvips&gifs=Yes&bproc=volrange&scode=6600%20-%206699 ER - TY - JOUR T1 - Mean-field treatment of the damping of the oscillations of a 1D Bose gas in an optical lattice JF - Physical Review A Y1 - 2006 A1 - Julio Gea-Banacloche A1 - Ana Maria Rey A1 - Guido Pupillo A1 - Carl J. Williams A1 - Charles W. Clark AB - We present a theoretical treatment of the surprisingly large damping observed recently in one-dimensional Bose-Einstein atomic condensates in optical lattices. We show that time-dependent Hartree-Fock-Bogoliubov (HFB) calculations can describe qualitatively the main features of the damping observed over a range of lattice depths. We also derive a formula of the fluctuation-dissipation type for the damping, based on a picture in which the coherent motion of the condensate atoms is disrupted as they try to flow through the random local potential created by the irregular motion of noncondensate atoms. We expect this irregular motion to result from the well-known dynamical instability exhibited by the mean-field theory for these systems. When parameters for the characteristic strength and correlation times of the fluctuations, obtained from the HFB calculations, are substituted in the damping formula, we find very good agreement with the experimentally-observed damping, as long as the lattice is shallow enough for the fraction of atoms in the Mott insulator phase to be negligible. We also include, for completeness, the results of other calculations based on the Gutzwiller ansatz, which appear to work better for the deeper lattices. VL - 73 UR - http://arxiv.org/abs/cond-mat/0410677v4 CP - 1 J1 - Phys. Rev. A U5 - 10.1103/PhysRevA.73.013605 ER - TY - JOUR T1 - Multichannel quantum-defect theory for slow atomic collisions JF - Physical Review A Y1 - 2005 A1 - Bo Gao A1 - Eite Tiesinga A1 - Carl J. Williams A1 - Paul S. Julienne AB - We present a multichannel quantum-defect theory for slow atomic collisions that takes advantages of the analytic solutions for the long-range potential, and both the energy and the angular-momentum insensitivities of the short-range parameters. The theory provides an accurate and complete account of scattering processes, including shape and Feshbach resonances, in terms of a few parameters such as the singlet and the triplet scattering lengths. As an example, results for $^{23}$Na-$^{23}$Na scattering are presented and compared close-coupling calculations. VL - 72 UR - http://arxiv.org/abs/physics/0508060v1 CP - 4 J1 - Phys. Rev. A U5 - 10.1103/PhysRevA.72.042719 ER - TY - JOUR T1 - Maxwell's demon and the thermodynamics of computation Y1 - 2002 A1 - J. Bub AB - It is generally accepted, following Landauer and Bennett, that the process of measurement involves no minimum entropy cost, but the erasure of information in resetting the memory register of a computer to zero requires dissipating heat into the environment. This thesis has been challenged recently in a two-part article by Earman and Norton. I review some relevant observations in the thermodynamics of computation and argue that Earman and Norton are mistaken: there is in principle no entropy cost to the acquisition of information, but the destruction of information does involve an irreducible entropy cost. UR - http://arxiv.org/abs/quant-ph/0203017v1 J1 - Studies in History and Philosophy of Modern Physics 32 ER - TY - JOUR T1 - Metric Equivalence of Path Spaces JF - Nonlinear Studies Y1 - 2000 A1 - Brad Lackey AB - Local equivalence and the invariants of systems of second order differential equations were studied in a series of papers by Kosambi, Cartan, and Chern. The resulting theory, deemed KCC-theory, is a rich geometric study which in many ways generalizes Riemannian and Finsler geometry. Yet, in many applications one requires a metric structure in addition to the systems of second order differential equations. We pose a geometry which is equipped with both of these structures, and solve the problem of local equivalence and thus determining a preferred connection and finding a generating set for all the invariants of the theory. VL - 7 CP - 2 ER - TY - JOUR T1 - A model of trophodynamics JF - Nonlinear Analysis: Theory, Methods & Applications Y1 - 1999 A1 - Brad Lackey PB - Pergamon VL - 35 U4 - 37–57 U5 - 10.1016/S0362-546X(98)00097-2 ER -