01538nas a2200169 4500008004100000022001400041245006400055210006400119260001400183300000900197490000600206520105300212100002201265700002401287700002001311856003701331 2024 eng d a2521-327X00aRandomized measurement protocols for lattice gauge theories0 aRandomized measurement protocols for lattice gauge theories c3/20/2024 a13000 v83 a

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

1 aBringewatt, Jacob1 aKunjummen, Jonathan1 aMueller, Niklas uhttps://arxiv.org/abs/2303.1551901429nas a2200157 4500008004100000245005600041210005600097260001300153520097200166100001801138700002301156700001801179700002101197700001601218856003701234 2023 eng d00aRandom Pulse Sequences for Qubit Noise Spectroscopy0 aRandom Pulse Sequences for Qubit Noise Spectroscopy c3/2/20233 a

Qubit noise spectroscopy is an important tool for the experimental investigation of open quantum systems. However, conventional techniques for implementing noise spectroscopy are time-consuming, because they require multiple measurements of the noise spectral density at different frequencies. Here we describe an alternative method for quickly characterizing the spectral density. Our method utilizes random pulse sequences, with carefully-controlled correlations among the pulses, to measure arbitrary linear functionals of the noise spectrum. Such measurements allow us to estimate k'th-order moments of the noise spectrum, as well as to reconstruct sparse noise spectra via compressed sensing. Our simulations of the performance of the random pulse sequences on a realistic physical system, self-assembled quantum dots, reveal a speedup of an order of magnitude in extracting the noise spectrum compared to conventional dynamical decoupling approaches.

1 aHuang, Kaixin1 aFarfurnik, Demitry1 aSeif, Alireza1 aHafezi, Mohammad1 aLiu, Yi-Kai uhttps://arxiv.org/abs/2303.0090901560nas a2200181 4500008004100000245006500041210005800106260001500164520103400179100001701213700002101230700002201251700002301273700002001296700001801316700002301334856002101357 2023 eng d00aOn the Rational Degree of Boolean Functions and Applications0 aRational Degree of Boolean Functions and Applications c10/12/20233 a

We study a natural complexity measure of Boolean functions known as the (exact) rational degree. For total functions f, it is conjectured that rdeg(f) is polynomially related to deg(f), where deg(f) is the Fourier degree. Towards this conjecture, we show that symmetric functions have rational degree at least deg(f)/2 and monotone functions have rational degree at least deg(f)−−−−−√. We observe that both of these lower bounds are tight. In addition, we show that all read-once depth-d Boolean formulae have rational degree at least Ω(deg(f)1/d). Furthermore, we show that almost every Boolean function on n variables has rational degree at least n/2−O(n−−√).
In contrast to total functions, we exhibit partial functions that witness unbounded separations between rational and approximate degree, in both directions. As a consequence, we show that for quantum computers, post-selection and bounded-error are incomparable resources in the black-box model.

1 aIyer, Vishnu1 aJain, Siddhartha1 aKovacs-Deak, Matt1 aKumar, Vinayak, M.1 aSchaeffer, Luke1 aWang, Daochen1 aWhitmeyer, Michael uarXiv:2310.0800401441nas a2200193 4500008004100000245006200041210006200103260001300165520087300178100001601051700001901067700001501086700001701101700002501118700002001143700002701163700002001190856003701210 2023 eng d00aRealization of 1D Anyons with Arbitrary Statistical Phase0 aRealization of 1D Anyons with Arbitrary Statistical Phase c6/2/20233 a

Low-dimensional quantum systems can host anyons, particles with exchange statistics that are neither bosonic nor fermionic. Despite indications of a wealth of exotic phenomena, the physics of anyons in one dimension (1D) remains largely unexplored. Here, we realize Abelian anyons in 1D with arbitrary exchange statistics using ultracold atoms in an optical lattice, where we engineer the statistical phase via a density-dependent Peierls phase. We explore the dynamical behavior of two anyons undergoing quantum walks, and observe the anyonic Hanbury Brown-Twiss effect, as well as the formation of bound states without on-site interactions. Once interactions are introduced, we observe spatially asymmetric transport in contrast to the symmetric dynamics of bosons and fermions. Our work forms the foundation for exploring the many-body behavior of 1D anyons.

1 aKwan, Joyce1 aSegura, Perrin1 aLi, Yanfei1 aKim, Sooshin1 aGorshkov, Alexey, V.1 aEckardt, André1 aBakkali-Hassani, Brice1 aGreiner, Markus uhttps://arxiv.org/abs/2306.0173701714nas a2200181 4500008004100000245004400041210004400085260001500129490000800144520120900152100002801361700002801389700002101417700002001438700001701458700002001475856003701495 2022 eng d00aResource theory of quantum uncomplexity0 aResource theory of quantum uncomplexity c12/19/20220 v1063 a

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

1 aHalpern, Nicole, Yunger1 aKothakonda, Naga, B. T.1 aHaferkamp, Jonas1 aMunson, Anthony1 aEisert, Jens1 aFaist, Philippe uhttps://arxiv.org/abs/2110.1137101565nas a2200169 4500008004100000245004300041210004200084260001400126520108300140100003001223700002001253700002101273700002501294700002101319700001801340856003701358 2021 eng d00aRainbow Scars: From Area to Volume Law0 aRainbow Scars From Area to Volume Law c7/12/20213 a

Quantum many-body scars (QMBS) constitute a new quantum dynamical regime in which rare "scarred" eigenstates mediate weak ergodicity breaking. One open question is to understand the most general setting in which these states arise. In this work, we develop a generic construction that embeds a new class of QMBS, rainbow scars, into the spectrum of an arbitrary Hamiltonian. Unlike other examples of QMBS, rainbow scars display extensive bipartite entanglement entropy while retaining a simple entanglement structure. Specifically, the entanglement scaling is volume-law for a random bipartition, while scaling for a fine-tuned bipartition is sub-extensive. When internal symmetries are present, the construction leads to multiple, and even towers of rainbow scars revealed through distinctive non-thermal dynamics. To this end, we provide an experimental road map for realizing rainbow scar states in a Rydberg-atom quantum simulator, leading to coherent oscillations distinct from the strictly sub-volume-law QMBS previously realized in the same system. 

1 aLanglett, Christopher, M.1 aYang, Zhi-Cheng1 aWildeboer, Julia1 aGorshkov, Alexey, V.1 aIadecola, Thomas1 aXu, Shenglong uhttps://arxiv.org/abs/2107.0341602275nas a2200193 4500008004100000245007200041210006900113260001500182490000600197520168200203100002401885700002101909700002601930700002301956700002301979700002302002700001902025856003702044 2021 eng d00aRay-based framework for state identification in quantum dot devices0 aRaybased framework for state identification in quantum dot devic c06/17/20210 v23 a

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

1 aZwolak, Justyna, P.1 aMcJunkin, Thomas1 aKalantre, Sandesh, S.1 aNeyens, Samuel, F.1 aMacQuarrie, E., R.1 aEriksson, Mark, A.1 aTaylor, J., M. uhttps://arxiv.org/abs/2102.1178401780nas a2200181 4500008004100000245006700041210006600108260001500174520113500189653002701324653003101351653004701382653005201429100002201481700003201503700002601535856003701561 2021 eng d00aRelaxation of non-integrable systems and correlation functions0 aRelaxation of nonintegrable systems and correlation functions c12/17/20213 a

We investigate early-time equilibration rates of observables in closed many-body quantum systems and compare them to those of two correlation functions, first introduced by Kubo and Srednicki. We explore whether these different rates coincide at a universal value that sets the timescales of processes at a finite energy density. We find evidence for this coincidence when the initial conditions are sufficiently generic, or typical. We quantify this with the effective dimension of the state and with a state-observable effective dimension, which estimate the number of energy levels that participate in the dynamics. Our findings are confirmed by proving that these different timescales coincide for dynamics generated by Haar-random Hamiltonians. This also allows to quantitatively understand the scope of previous theoretical results on equilibration timescales and on random matrix formalisms. We approach this problem with exact, full spectrum diagonalization. The numerics are carried out in a non-integrable Heisenberg-like Hamiltonian, and the dynamics are investigated for several pairs of observables and states.

10aFOS: Physical sciences10aQuantum Physics (quant-ph)10aStatistical Mechanics (cond-mat.stat-mech)10aStrongly Correlated Electrons (cond-mat.str-el)1 aRiddell, Jonathon1 aGarcía-Pintos, Luis, Pedro1 aAlhambra, Álvaro, M. uhttps://arxiv.org/abs/2112.0947501694nas a2200169 4500008004100000245004400041210004400085260001500129520120900144100002801353700002801381700002101409700002001430700001701450700002001467856003701487 2021 eng d00aResource theory of quantum uncomplexity0 aResource theory of quantum uncomplexity c10/21/20213 a

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

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

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

1 aWang, Qingfeng1 aLi, Ming1 aMonroe, Christopher1 aNam, Yunseong uhttps://arxiv.org/abs/2004.0415101478nas a2200277 4500008004100000245005400041210005300095260001400148300001100162490000800173520078100181100001300962700001300975700001600988700001901004700001401023700001801037700001401055700001601069700001401085700001101099700001701110700001801127700001801145856003701163 2021 eng d00aRobust Self-Testing of Multiparticle Entanglement0 aRobust SelfTesting of Multiparticle Entanglement c12/7/2021 a2305030 v1273 a

Quantum self-testing is a device-independent way to certify quantum states and measurements using only the input-output statistics, with minimal assumptions about the quantum devices. Due to the high demand on tolerable noise, however, experimental self-testing was limited to two-photon systems. Here, we demonstrate the first robust self-testing for multi-particle quantum entanglement. We prepare two examples of four-photon graph states, the Greenberger-Horne-Zeilinger (GHZ) states with a fidelity of 0.957(2) and the linear cluster states with a fidelity of 0.945(2). Based on the observed input-output statistics, we certify the genuine four-photon entanglement and further estimate their qualities with respect to realistic noise in a device-independent manner.

1 aWu, Dian1 aZhao, Qi1 aGu, Xue-Mei1 aZhong, Han-Sen1 aZhou, You1 aPeng, Li-Chao1 aQin, Jian1 aLuo, Yi-Han1 aChen, Kai1 aLi, Li1 aLe Liu, Nai-1 aLu, Chao-Yang1 aPan, Jian-Wei uhttps://arxiv.org/abs/2105.1029801423nas a2200145 4500008004100000245005800041210005300099260001400152520098400166100001801150700003701168700001601205700001901221856003701240 2021 eng d00aRPPLNS: Pay-per-last-N-shares with a Randomised Twist0 aRPPLNS PayperlastNshares with a Randomised Twist c2/15/20213 a

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

1 aLazos, Philip1 aMarmolejo-Cossío, Francisco, J.1 aZhou, Xinyu1 aKatz, Jonathan uhttps://arxiv.org/abs/2102.0768101387nas a2200157 4500008004100000245002900041210002900070260001300099490000600112520096500118100002501083700003201108700003201140700002001172856003701192 2020 eng d00aRandom Quantum Batteries0 aRandom Quantum Batteries c5/5/20200 v23 a

Quantum nano-devices are fundamental systems in quantum thermodynamics that have been the subject of profound interest in recent years. Among these, quantum batteries play a very important role. In this paper we lay down a theory of random quantum batteries and provide a systematic way of computing the average work and work fluctuations in such devices by investigating their typical behavior. We show that the performance of random quantum batteries exhibits typicality and depends only on the spectral properties of the time evolving operator, the initial state and the measuring Hamiltonian. At given revival times a random quantum battery features a quantum advantage over classical random batteries. Our method is particularly apt to be used both for exactly solvable models like the Jaynes-Cummings model or in perturbation theory, e.g., systems subject to harmonic perturbations. We also study the setting of quantum adiabatic random batteries.

1 aCaravelli, Francesco1 aDe Wit, Ghislaine, Coulter-1 aGarcía-Pintos, Luis, Pedro1 aHamma, Alioscia uhttps://arxiv.org/abs/1908.0806401689nas a2200145 4500008004100000245002500041210002500066260001400091520132300105100002101428700001601449700002001465700002101485856003701506 2020 eng d00aRaw Image Deblurring0 aRaw Image Deblurring c12/8/20203 a

Deep learning-based blind image deblurring plays an essential role in solving image blur since all existing kernels are limited in modeling the real world blur. Thus far, researchers focus on powerful models to handle the deblurring problem and achieve decent results. For this work, in a new aspect, we discover the great opportunity for image enhancement (e.g., deblurring) directly from RAW images and investigate novel neural network structures benefiting RAW-based learning. However, to the best of our knowledge, there is no available RAW image deblurring dataset. Therefore, we built a new dataset containing both RAW images and processed sRGB images and design a new model to utilize the unique characteristics of RAW images. The proposed deblurring model, trained solely from RAW images, achieves the state-of-art performance and outweighs those trained on processed sRGB images. Furthermore, with fine-tuning, the proposed model, trained on our new dataset, can generalize to other sensors. Additionally, by a series of experiments, we demonstrate that existing deblurring models can also be improved by training on the RAW images in our new dataset. Ultimately, we show a new venue for further opportunities based on the devised novel raw-based deblurring method and the brand-new Deblur-RAW dataset.

1 aLiang, Chih-Hung1 aChen, Yu-An1 aLiu, Yueh-Cheng1 aHsu, Winston, H. uhttps://arxiv.org/abs/2012.0426401423nas a2200157 4500008004100000245006500041210006300106260001400169520093400183100002401117700002601141700002101167700002101188700001901209856003701228 2020 eng d00aRay-based classification framework for high-dimensional data0 aRaybased classification framework for highdimensional data c10/1/20203 a

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

1 aZwolak, Justyna, P.1 aKalantre, Sandesh, S.1 aMcJunkin, Thomas1 aWeber, Brian, J.1 aTaylor, J., M. uhttps://arxiv.org/abs/2010.0050001634nas a2200157 4500008004100000245007000041210006900111260001400180520114300194100001601337700001901353700002401372700001801396700002501414856003701439 2020 eng d00aRealizing and Probing Baryonic Excitations in Rydberg Atom Arrays0 aRealizing and Probing Baryonic Excitations in Rydberg Atom Array c7/14/20203 a

We propose a realization of mesonic and baryonic quasiparticle excitations in Rydberg atom arrays with programmable interactions. Recent experiments have shown that such systems possess a Z3-ordered crystalline phase whose low-energy quasiparticles are defects in the crystalline order. By engineering a Z3-translational-symmetry breaking field on top of the Rydberg-blockaded Hamiltonian, we show that different types of defects experience confinement, and as a consequence form mesonic or baryonic quasiparticle excitations. We illustrate the formation of these quasiparticles by studying a quantum chiral clock model related to the Rydberg Hamiltonian. We then propose an experimental protocol involving out-of-equilibrium dynamics to directly probe the spectrum of the confined excitations. We show that the confined quasiparticle spectrum can limit quantum information spreading in this system. This proposal is readily applicable to current Rydberg experiments, and the method can be easily generalized to more complex confined excitations (e.g. `tetraquarks', `pentaquarks') in phases with Zq order for q>3. 

1 aLiu, Fangli1 aWhitsitt, Seth1 aBienias, Przemyslaw1 aLundgren, Rex1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2007.0725801558nas a2200217 4500008004100000245008100041210006900122260001500191520086200206100002301068700001601091700002401107700002101131700003001152700002801182700002401210700001801234700002601252700002501278856003701303 2020 eng d00aResonant enhancement of three-body loss between strongly interacting photons0 aResonant enhancement of threebody loss between strongly interact c10/19/20203 a

Rydberg polaritons provide an example of a rare type of system where three-body interactions can be as strong or even stronger than two-body interactions. The three-body interactions can be either dispersive or dissipative, with both types possibly giving rise to exotic, strongly-interacting, and topological phases of matter. Despite past theoretical and experimental studies of the regime with dispersive interaction, the dissipative regime is still mostly unexplored. Using a renormalization group technique to solve the three-body Schrödinger equation, we show how the shape and strength of dissipative three-body forces can be universally enhanced for Rydberg polaritons. We demonstrate how these interactions relate to the transmission through a single-mode cavity, which can be used as a probe of the three-body physics in current experiment

1 aKalinowski, Marcin1 aWang, Yidan1 aBienias, Przemyslaw1 aGullans, Michael1 aOrnelas-Huerta, Dalia, P.1 aCraddock, Alexander, N.1 aRolston, Steven, L.1 aPorto, J., V.1 aBüchler, Hans, Peter1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2010.0977201214nas a2200145 4500008004100000245004500041210004500086260001300131490000700144520081700151100002300968700002100991700001901012856003701031 2020 eng d00aRobust Encoding of a Qubit in a Molecule0 aRobust Encoding of a Qubit in a Molecule c9/1/20200 v103 a

We construct quantum error-correcting codes that embed a finite-dimensional code space in the infinite-dimensional Hilbert space of rotational states of a rigid body. These codes, which protect against both drift in the body’s orientation and small changes in its angular momentum, may be well suited for robust storage and coherent processing of quantum information using rotational states of a polyatomic molecule. Extensions of such codes to rigid bodies with a symmetry axis are compatible with rotational states of diatomic molecules as well as nuclear states of molecules and atoms. We also describe codes associated with general non-Abelian groups and develop orthogonality relations for coset spaces, laying the groundwork for quantum information processing with exotic configuration spaces.

1 aAlbert, Victor, V.1 aCovey, Jacob, P.1 aPreskill, John uhttps://arxiv.org/abs/1911.0009901837nas a2200157 4500008004100000245006500041210006400106260001500170520136000185100002001545700001601565700001901581700002501600700001701625856003701642 2019 eng d00aReal-time dynamics of string breaking in quantum spin chains0 aRealtime dynamics of string breaking in quantum spin chains c2019/11/263 a

String breaking is a central dynamical process in theories featuring confinement, where a string connecting two charges decays at the expense of the creation of new particle-antiparticle pairs. Here, we show that this process can also be observed in quantum Ising chains where domain walls get confined either by a symmetry-breaking field or by long-range interactions. We find that string breaking occurs, in general, as a two-stage process: First, the initial charges remain essentially static and stable. The connecting string, however, can become a dynamical object. We develop an effective description of this motion, which we find is strongly constrained. In the second stage, which can be severely delayed due to these dynamical constraints, the string finally breaks. We observe that the associated time scale can depend crucially on the initial separation between domain walls and can grow by orders of magnitude by changing the distance by just a few lattice sites. We discuss how our results generalize to one-dimensional confining gauge theories and how they can be made accessible in quantum simulator experiments such as Rydberg atoms or trapped ions.

1 aVerdel, Roberto1 aLiu, Fangli1 aWhitsitt, Seth1 aGorshkov, Alexey, V.1 aHeyl, Markus uhttps://arxiv.org/abs/1911.1138201498nas a2200121 4500008004100000245007200041210006900113260001300182520109600195100002501291700002301316856003701339 2019 eng d00aRefining the Structure of Neural Networks Using Matrix Conditioning0 aRefining the Structure of Neural Networks Using Matrix Condition c8/6/20193 a

Deep learning models have proven to be exceptionally useful in performing many machine learning tasks. However, for each new dataset, choosing an effective size and structure of the model can be a time-consuming process of trial and error. While a small network with few neurons might not be able to capture the intricacies of a given task, having too many neurons can lead to overfitting and poor generalization. Here, we propose a practical method that employs matrix conditioning to automatically design the structure of layers of a feed-forward network, by first adjusting the proportion of neurons among the layers of a network and then scaling the size of network up or down. Results on sample image and non-image datasets demonstrate that our method results in small networks with high accuracies. Finally, guided by matrix conditioning, we provide a method to effectively squeeze models that are already trained. Our techniques reduce the human cost of designing deep learning models and can also reduce training time and the expense of using neural networks for applications.

1 aYousefzadeh, Roozbeh1 aO'Leary, Dianne, P uhttps://arxiv.org/abs/1908.0240001259nas a2200145 4500008004100000245005700041210005600098490000800154520083800162100001701000700002101017700001701038700002101055856003701076 2019 eng d00aReQWIRE: Reasoning about Reversible Quantum Circuits0 aReQWIRE Reasoning about Reversible Quantum Circuits0 v2873 a

Common quantum algorithms make heavy use of ancillae: scratch qubits that are initialized at some state and later returned to that state and discarded. Existing quantum circuit languages let programmers assert that a qubit has been returned to the |0> state before it is discarded, allowing for a range of optimizations. However, existing languages do not provide the tools to verify these assertions, introducing a potential source of errors. In this paper we present methods for verifying that ancillae are discarded in the desired state, and use these methods to implement a verified compiler from classical functions to quantum oracles.

1 aRand, Robert1 aPaykin, Jennifer1 aLee, Dong-Ho1 aZdancewic, Steve uhttps://arxiv.org/abs/1901.1011802223nas a2200121 4500008004100000245007400041210006900115260001500184520183100199100001402030700002002044856003702064 2019 eng d00aResource theory of asymmetric distinguishability for quantum channels0 aResource theory of asymmetric distinguishability for quantum cha c07/15/20193 a

This paper develops the resource theory of asymmetric distinguishability for quantum channels, generalizing the related resource theory for states [arXiv:1006.0302, arXiv:1905.11629]. The key constituents of the channel resource theory are quantum channel boxes, consisting of a pair of quantum channels, which can be manipulated for free by means of an arbitrary quantum superchannel (the most general physical transformation of a quantum channel). One main question of the resource theory is the approximate channel box transformation problem, in which the goal is to transform an initial channel box (or boxes) to a final channel box (or boxes), while allowing for an asymmetric error in the transformation. The channel resource theory is richer than its counterpart for states because there is a wider variety of ways in which this question can be framed, either in the one-shot or n-shot regimes, with the latter having parallel and sequential variants. As in [arXiv:1905.11629], we consider two special cases of the general channel box transformation problem, known as distinguishability distillation and dilution. For the one-shot case, we find that the optimal values of the various tasks are equal to the non-smooth or smooth channel min- or max-relative entropies, thus endowing all of these quantities with operational interpretations. In the asymptotic sequential setting, we prove that the exact distinguishability cost is equal to channel max-relative entropy and the distillable distinguishability is equal to the amortized channel relative entropy of [arXiv:1808.01498]. This latter result can also be understood as a solution to Stein's lemma for quantum channels in the sequential setting. Finally, the theory simplifies significantly for environment-seizable and classical--quantum channel boxes.

1 aWang, Xin1 aWilde, Mark, M. uhttps://arxiv.org/abs/1907.0630601752nas a2200145 4500008004100000245006700041210006700108260001500175520130600190100001901496700002001515700001401535700002001549856003701569 2019 eng d00aResource theory of entanglement for bipartite quantum channels0 aResource theory of entanglement for bipartite quantum channels c07/08/20193 a

The traditional perspective in quantum resource theories concerns how to use free operations to convert one resourceful quantum state to another one. For example, a fundamental and well known question in entanglement theory is to determine the distillable entanglement of a bipartite state, which is equal to the maximum rate at which fresh Bell states can be distilled from many copies of a given bipartite state by employing local operations and classical communication for free. It is the aim of this paper to take this kind of question to the next level, with the main question being: What is the best way of using free channels to convert one resourceful quantum channel to another? Here we focus on the the resource theory of entanglement for bipartite channels and establish several fundamental tasks and results regarding it. In particular, we establish bounds on several pertinent information processing tasks in channel entanglement theory, and we define several entanglement measures for bipartite channels, including the logarithmic negativity and the κ-entanglement. We also show that the max-Rains information of [Bäuml et al., Physical Review Letters, 121, 250504 (2018)] has a divergence interpretation, which is helpful for simplifying the results of this earlier work. 

1 aBäuml, Stefan1 aDas, Siddhartha1 aWang, Xin1 aWilde, Mark, M. uhttps://arxiv.org/abs/1907.0418102434nas a2200205 4500008004100000245006200041210006200103260001500165300001100180490000800191520186900199100001502068700001902083700001902102700001602121700001702137700001702154700002002171856003702191 2018 eng d00aRecovering quantum gates from few average gate fidelities0 aRecovering quantum gates from few average gate fidelities c2018/03/01 a1705020 v1213 a

Characterising quantum processes is a key task in and constitutes a challenge for the development of quantum technologies, especially at the noisy intermediate scale of today's devices. One method for characterising processes is randomised benchmarking, which is robust against state preparation and measurement (SPAM) errors, and can be used to benchmark Clifford gates. A complementing approach asks for full tomographic knowledge. Compressed sensing techniques achieve full tomography of quantum channels essentially at optimal resource efficiency. So far, guarantees for compressed sensing protocols rely on unstructured random measurements and can not be applied to the data acquired from randomised benchmarking experiments. It has been an open question whether or not the favourable features of both worlds can be combined. In this work, we give a positive answer to this question. For the important case of characterising multi-qubit unitary gates, we provide a rigorously guaranteed and practical reconstruction method that works with an essentially optimal number of average gate fidelities measured respect to random Clifford unitaries. Moreover, for general unital quantum channels we provide an explicit expansion into a unitary 2-design, allowing for a practical and guaranteed reconstruction also in that case. As a side result, we obtain a new statistical interpretation of the unitarity -- a figure of merit that characterises the coherence of a process. In our proofs we exploit recent representation theoretic insights on the Clifford group, develop a version of Collins' calculus with Weingarten functions for integration over the Clifford group, and combine this with proof techniques from compressed sensing.

1 aRoth, Ingo1 aKueng, Richard1 aKimmel, Shelby1 aLiu, Yi-Kai1 aGross, David1 aEisert, Jens1 aKliesch, Martin uhttps://arxiv.org/abs/1803.0057201111nas a2200109 4500008004100000245004900041210004900090520079100139100001900930700001500949856003700964 2018 eng d00aRecovery Map for Fermionic Gaussian Channels0 aRecovery Map for Fermionic Gaussian Channels3 a

A recovery map effectively cancels the action of a quantum operation to a partial or full extent. We study the Petz recovery map in the case where the quantum channel and input states are fermionic and Gaussian. Gaussian states are convenient because they are totally determined by their covariance matrix and because they form a closed set under so-called Gaussian channels. Using a Grassmann representation of fermionic Gaussian maps, we show that the Petz recovery map is also Gaussian and determine it explicitly in terms of the covariance matrix of the reference state and the data of the channel. As a by-product, we obtain a formula for the fidelity between two fermionic Gaussian states. We also discuss subtleties arising from the singularities of the involved matrices.

1 aSwingle, Brian1 aWang, Yixu uhttps://arxiv.org/abs/1811.0495601416nas a2200133 4500008004100000245004200041210004200083260001500125490000600140520105200146100001901198700002801217856003701245 2018 eng d00aResilience of scrambling measurements0 aResilience of scrambling measurements c2018/06/180 vA3 a

Most experimental protocols for measuring scrambling require time evolution with a Hamiltonian and with the Hamiltonian's negative counterpart (backwards time evolution). Engineering controllable quantum many-body systems for which such forward and backward evolution is possible is a significant experimental challenge. Furthermore, if the system of interest is quantum-chaotic, one might worry that any small errors in the time reversal will be rapidly amplified, obscuring the physics of scrambling. This paper undermines this expectation: We exhibit a renormalization protocol that extracts nearly ideal out-of-time-ordered-correlator measurements from imperfect experimental measurements. We analytically and numerically demonstrate the protocol's effectiveness, up to the scrambling time, in a variety of models and for sizable imperfections. The scheme extends to errors from decoherence by an environment.

1 aSwingle, Brian1 aHalpern, Nicole, Yunger uhttps://arxiv.org/abs/1802.0158701439nas a2200205 4500008004100000245005100041210005100092260001500143300001200158490000800170520087500178100001801053700002201071700001301093700001601106700001901122700001901141700001801160856005501178 2018 eng d00aResonantly driven CNOT gate for electron spins0 aResonantly driven CNOT gate for electron spins c2018/01/26 a439-4420 v3593 a

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

1 aZajac, D., M.1 aSigillito, A., J.1 aRuss, M.1 aBorjans, F.1 aTaylor, J., M.1 aBurkard, Guido1 aPetta, J., R. uhttp://science.sciencemag.org/content/359/6374/43901532nas a2200193 4500008004100000245009300041210006900134260001500203300001100218490000800229520089100237100002101128700002401149700002201173700002301195700002401218700002301242856007301265 2018 eng d00aRobust two-qubit gates in a linear ion crystal using a frequency-modulated driving force0 aRobust twoqubit gates in a linear ion crystal using a frequencym c2018/01/09 a0205010 v1203 a

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

1 aLeung, Pak, Hong1 aLandsman, Kevin, A.1 aFiggatt, Caroline1 aLinke, Norbert, M.1 aMonroe, Christopher1 aBrown, Kenneth, R. uhttps://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.02050101545nas a2200145 4500008004100000245006100041210006100102260001500163300001400178490000700192520113000199100001701329700001601346856003701362 2017 eng d00aRandomness in nonlocal games between mistrustful players0 aRandomness in nonlocal games between mistrustful players c2017/06/15 a0595-06100 v173 a

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

1 aMiller, Carl1 aShi, Yaoyun uhttps://arxiv.org/abs/1706.0498401278nas a2200133 4500008004100000245005800041210005700099260001500156520087600171100001501047700001701062700001601079856004901095 2017 eng d00aRaz-McKenzie simulation with the inner product gadget0 aRazMcKenzie simulation with the inner product gadget c2017/01/283 a

In this note we show that the Raz-McKenzie simulation algorithm which lifts deterministic query lower bounds to deterministic communication lower bounds can be implemented for functions f composed with the Inner Product gadget 1ip(x, y) = P i xiyi mod 2 of logarithmic size. In other words, given a function f : {0, 1} n → {0, 1} with deterministic query complexity D(f), we show that the deterministic communication complexity of the composed function f ◦ 1 n ip is Θ(D(f) log n), where f ◦ 1 n ip(x, y) = f(1ip(x 1 , y 1 ), . . . , 1ip(x n , y n )) where x = (x 1 , . . . , x n ), y = (y 1 , . . . , y n ) and each x i and y i are O(log n) bit strings. In [RM97] and [GPW15], the simulation algorithm is implemented for functions composed with the Indexing gadget, where the size of the gadget is polynomial in the input length of the outer function f.

1 aWu, Xiaodi1 aYao, Penghui1 aYuen, Henry uhttps://eccc.weizmann.ac.il/report/2017/010/02646nas 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 a

There 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/1708.0978001315nas a2200145 4500008004100000245004100041210004100082260001500123300001100138490000600149520091300155100001601068700001701084856006801101 2017 eng d00aRigidity of the magic pentagram game0 aRigidity of the magic pentagram game c2017/11/02 a0150020 v33 a

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

1 aKalev, Amir1 aMiller, Carl uhttp://iopscience.iop.org/article/10.1088/2058-9565/aa931d/meta01605nas a2200121 4500008004100000245006800041210006800109260001500177520121600192100001901408700001901427856003701446 2017 eng d00aRobust entanglement renormalization on a noisy quantum computer0 aRobust entanglement renormalization on a noisy quantum computer c2017/11/203 a

A method to study strongly interacting quantum many-body systems at and away from criticality is proposed. The method is based on a MERA-like tensor network that can be efficiently and reliably contracted on a noisy quantum computer using a number of qubits that is much smaller than the system size. We prove that the outcome of the contraction is stable to noise and that the estimated energy upper bounds the ground state energy. The stability, which we numerically substantiate, follows from the positivity of operator scaling dimensions under renormalization group flow. The variational upper bound follows from a particular assignment of physical qubits to different locations of the tensor network plus the assumption that the noise model is local. We postulate a scaling law for how well the tensor network can approximate ground states of lattice regulated conformal field theories in d spatial dimensions and provide evidence for the postulate. Under this postulate, a O(logd (1/δ))-qubit quantum computer can prepare a valid quantum-mechanical state with energy density δ above the ground state. In the presence of noise, δ = O( logd+1(1/)) can be achieved, where  is the noise strength.

1 aKim, Isaac, H.1 aSwingle, Brian uhttps://arxiv.org/abs/1711.0750001353nas a2200181 4500008004100000245006400041210006200105260001500167490000700182520077900189100002700968700001900995700002401014700002301038700001701061700002501078856006801103 2016 eng d00aRealizing Exactly Solvable SU(N) Magnets with Thermal Atoms0 aRealizing Exactly Solvable SUN Magnets with Thermal Atoms c2016/05/060 v933 a

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

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

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

10akey distribution10anonlocal games10aprivacy10aquantum cryptography10arandom-number generation10auntrusted device1 aMiller, Carl1 aShi, Yaoyun uhttp://doi.acm.org/10.1145/288549301534nas a2200157 4500008004100000245007200041210006900113260001500182300001100197490000700208520106200215100001901277700002001296700002401316856003601340 2015 eng d00aRobust Single-Qubit Process Calibration via Robust Phase Estimation0 aRobust SingleQubit Process Calibration via Robust Phase Estimati c2015/12/08 a0623150 v923 a An important step in building a quantum computer is calibrating experimentally implemented quantum gates to produce operations that are close to ideal unitaries. The calibration step involves estimating the error in gates and then using controls to correct the implementation. Quantum process tomography is a standard technique for estimating these errors, but is both time consuming, (when one only wants to learn a few key parameters), and requires resources, like perfect state preparation and measurement, that might not be available. With the goal of efficiently estimating specific errors using minimal resources, we develop a parameter estimation technique, which can gauge two key parameters (amplitude and off-resonance errors) in a single-qubit gate with provable robustness and efficiency. In particular, our estimates achieve the optimal efficiency, Heisenberg scaling. Our main theorem making this possible is a robust version of the phase estimation procedure of Higgins et al. [B. L. Higgins, New J. Phys. 11, 073023 (2009)]. 1 aKimmel, Shelby1 aLow, Guang, Hao1 aYoder, Theodore, J. uhttp://arxiv.org/abs/1502.0267701095nas a2200157 4500008004100000245009500041210007100136260001500207300001100222490000700233520056700240100001600807700002300823700002300846856006800869 2014 eng d00aRemote tomography and entanglement swapping via von Neumann–Arthurs–Kelly interaction 0 aRemote tomography and entanglement swapping via von Neumann–Arth c2014/05/09 a0521070 v893 aWe propose an interaction-based method for remote tomography and entanglement swapping. Alice arranges a von Neumann-Arthurs-Kelly interaction between a system particle P and two apparatus particles A1,A2, and then transports the latter to Bob. Bob can reconstruct the unknown initial state of particle P not received by him by quadrature measurements on A1,A2. Further, if another particle P′ in Alice's hands is EPR entangled with P, it will be EPR entangled with the distant pair A1,A2. This method will be contrasted with the usual teleportation protocols.1 aRoy, S., M.1 aDeshpande, Abhinav1 aSakharwade, Nitica uhttp://journals.aps.org/pra/abstract/10.1103/PhysRevA.89.05210701337nas a2200169 4500008004100000245007700041210006900118260001400187490000600201520082000207100001901027700002501046700001901071700002301090700001701113856003701130 2014 eng d00aRobust Extraction of Tomographic Information via Randomized Benchmarking0 aRobust Extraction of Tomographic Information via Randomized Benc c2014/3/250 v43 a We describe how randomized benchmarking can be used to reconstruct the unital part of any trace-preserving quantum map, which in turn is sufficient for the full characterization of any unitary evolution, or more generally, any unital trace-preserving evolution. This approach inherits randomized benchmarking's robustness to preparation and measurement imperfections, therefore avoiding systematic errors caused by these imperfections. We also extend these techniques to efficiently estimate the average fidelity of a quantum map to unitary maps outside of the Clifford group. The unitaries we consider include operations commonly used to achieve universal quantum computation in a fault-tolerant setting. In addition, we rigorously bound the time and sampling complexities of randomized benchmarking procedures. 1 aKimmel, Shelby1 ada Silva, Marcus, P.1 aRyan, Colm, A.1 aJohnson, Blake, R.1 aOhki, Thomas uhttp://arxiv.org/abs/1306.2348v101351nas a2200181 4500008004100000245006100041210006100102260001400163490000800177520081800185100002001003700002501023700002301048700002601071700001201097700002301109856003701132 2013 eng d00aRealizing Fractional Chern Insulators with Dipolar Spins0 aRealizing Fractional Chern Insulators with Dipolar Spins c2013/4/290 v1103 a Strongly correlated quantum systems can exhibit exotic behavior controlled by topology. We predict that the \nu=1/2 fractional Chern insulator arises naturally in a two-dimensional array of driven, dipolar-interacting spins. As a specific implementation, we analyze how to prepare and detect synthetic gauge potentials for the rotational excitations of ultra-cold polar molecules trapped in a deep optical lattice. While the orbital motion of the molecules is pinned, at finite densities, the rotational excitations form a fractional Chern insulator. We present a detailed experimental blueprint for KRb, and demonstrate that the energetics are consistent with near-term capabilities. Prospects for the realization of such phases in solid-state dipolar systems are discussed as are their possible applications. 1 aYao, Norman, Y.1 aGorshkov, Alexey, V.1 aLaumann, Chris, R.1 aLäuchli, Andreas, M.1 aYe, Jun1 aLukin, Mikhail, D. uhttp://arxiv.org/abs/1212.4839v101080nas a2200193 4500008004100000245003200041210002800073260001400101490000800115520060900123100001600732700001300748700001900761700001900780700001100799700002000810700001900830856003700849 2013 eng d00aThe Resonant Exchange Qubit0 aResonant Exchange Qubit c2013/7/310 v1113 aWe introduce a solid-state qubit in which exchange interactions among confined electrons provide both the static longitudinal field and the oscillatory transverse field, allowing rapid and full qubit control via rf gate-voltage pulses. We demonstrate two-axis control at a detuning sweet-spot, where leakage due to hyperfine coupling is suppressed by the large exchange gap. A {\pi}/2-gate time of 2.5 ns and a coherence time of 19 {\mu}s, using multi-pulse echo, are also demonstrated. Model calculations that include effects of hyperfine noise are in excellent quantitative agreement with experiment. 1 aMedford, J.1 aBeil, J.1 aTaylor, J., M.1 aRashba, E., I.1 aLu, H.1 aGossard, A., C.1 aMarcus, C., M. uhttp://arxiv.org/abs/1304.3413v201124nas a2200181 4500008004100000245005300041210005300094260001500147300001100162490000700173520063000180100001800810700001800828700002400846700002100870700001400891856003700905 2012 eng d00aRank Reduction for the Local Consistency Problem0 aRank Reduction for the Local Consistency Problem c2012/02/09 a0222020 v533 a We address the problem of how simple a solution can be for a given quantum local consistency instance. More specifically, we investigate how small the rank of the global density operator can be if the local constraints are known to be compatible. We prove that any compatible local density operators can be satisfied by a low rank global density operator. Then we study both fermionic and bosonic versions of the N-representability problem as applications. After applying the channel-state duality, we prove that any compatible local channels can be obtained through a global quantum channel with small Kraus rank. 1 aChen, Jianxin1 aJi, Zhengfeng1 aKlyachko, Alexander1 aKribs, David, W.1 aZeng, Bei uhttp://arxiv.org/abs/1106.3235v200674nas a2200193 4500008004100000245006100041210005900102260001500161520012900176100001700305700001900322700001800341700001700359700001600376700001600392700001800408700001700426856003700443 2012 eng d00aReply to Comment on "Space-Time Crystals of Trapped Ions0 aReply to Comment on SpaceTime Crystals of Trapped Ions c2012/10/153 a This is a reply to the comment from Patrick Bruno (arXiv:1211.4792) on our paper (Phys. Rev. Lett. 109, 163001 (2012)). 1 aLi, Tongcang1 aGong, Zhe-Xuan1 aYin, Zhang-qi1 aQuan, H., T.1 aYin, Xiaobo1 aZhang, Peng1 aDuan, L., -M.1 aZhang, Xiang uhttp://arxiv.org/abs/1212.6959v201195nas a2200157 4500008004100000245006200041210006200103260001300165490000700178520072500185100002200910700001900932700002600951700002300977856003701000 2012 eng d00aResonant control of polar molecules in an optical lattice0 aResonant control of polar molecules in an optical lattice c2012/2/80 v853 a We study the resonant control of two nonreactive polar molecules in an optical lattice site, focussing on the example of RbCs. Collisional control can be achieved by tuning bound states of the intermolecular dipolar potential, by varying the applied electric field or trap frequency. We consider a wide range of electric fields and trapping geometries, showing that a three-dimensional optical lattice allows for significantly wider avoided crossings than free space or quasi-two dimensional geometries. Furthermore, we find that dipolar confinement induced resonances can be created with reasonable trapping frequencies and electric fields, and have widths that will enable useful control in forthcoming experiments. 1 aHanna, Thomas, M.1 aTiesinga, Eite1 aMitchell, William, F.1 aJulienne, Paul, S. uhttp://arxiv.org/abs/1111.0227v101287nas a2200181 4500008004100000245007300041210006900114260001400183490000800197520074600205100002000951700001400971700002600985700002501011700001201036700002001048856003701068 2011 eng d00aResolved atomic interaction sidebands in an optical clock transition0 aResolved atomic interaction sidebands in an optical clock transi c2011/6/220 v1063 a We report the observation of resolved atomic interaction sidebands (ISB) in the ${}^{87}$Sr optical clock transition when atoms at microkelvin temperatures are confined in a two-dimensional (2D) optical lattice. The ISB are a manifestation of the strong interactions that occur between atoms confined in a quasi-one-dimensional geometry and disappear when the confinement is relaxed along one dimension. The emergence of ISB is linked to the recently observed suppression of collisional frequency shifts in [1]. At the current temperatures, the ISB can be resolved but are broad. At lower temperatures, ISB are predicted to be substantially narrower and usable as powerful spectroscopic tools in strongly interacting alkaline-earth gases. 1 aBishof, Michael1 aLin, Yige1 aSwallows, Matthew, D.1 aGorshkov, Alexey, V.1 aYe, Jun1 aRey, Ana, Maria uhttp://arxiv.org/abs/1102.1016v201404nas a2200193 4500008004100000245006800041210006800109260001400177490000800191520083700199100002001036700001701056700002501073700001901098700001501117700001801132700002301150856003701173 2011 eng d00aRobust Quantum State Transfer in Random Unpolarized Spin Chains0 aRobust Quantum State Transfer in Random Unpolarized Spin Chains c2011/1/270 v1063 a We propose and analyze a new approach for quantum state transfer between remote spin qubits. Specifically, we demonstrate that coherent quantum coupling between remote qubits can be achieved via certain classes of random, unpolarized (infinite temperature) spin chains. Our method is robust to coupling strength disorder and does not require manipulation or control over individual spins. In principle, it can be used to attain perfect state transfer over arbitrarily long range via purely Hamiltonian evolution and may be particularly applicable in a solid-state quantum information processor. As an example, we demonstrate that it can be used to attain strong coherent coupling between Nitrogen-Vacancy centers separated by micrometer distances at room temperature. Realistic imperfections and decoherence effects are analyzed. 1 aYao, Norman, Y.1 aJiang, Liang1 aGorshkov, Alexey, V.1 aGong, Zhe-Xuan1 aZhai, Alex1 aDuan, L., -M.1 aLukin, Mikhail, D. uhttp://arxiv.org/abs/1011.2762v201937nas a2200133 4500008004100000245007500041210006600116260001500182300001400197490000800211520152400219100002301743856003701766 2010 eng d00aOn the relationship between continuous- and discrete-time quantum walk0 arelationship between continuous and discretetime quantum walk c2009/10/10 a581 - 6030 v2943 a Quantum walk is one of the main tools for quantum algorithms. Defined by analogy to classical random walk, a quantum walk is a time-homogeneous quantum process on a graph. Both random and quantum walks can be defined either in continuous or discrete time. But whereas a continuous-time random walk can be obtained as the limit of a sequence of discrete-time random walks, the two types of quantum walk appear fundamentally different, owing to the need for extra degrees of freedom in the discrete-time case. In this article, I describe a precise correspondence between continuous- and discrete-time quantum walks on arbitrary graphs. Using this correspondence, I show that continuous-time quantum walk can be obtained as an appropriate limit of discrete-time quantum walks. The correspondence also leads to a new technique for simulating Hamiltonian dynamics, giving efficient simulations even in cases where the Hamiltonian is not sparse. The complexity of the simulation is linear in the total evolution time, an improvement over simulations based on high-order approximations of the Lie product formula. As applications, I describe a continuous-time quantum walk algorithm for element distinctness and show how to optimally simulate continuous-time query algorithms of a certain form in the conventional quantum query model. Finally, I discuss limitations of the method for simulating Hamiltonians with negative matrix elements, and present two problems that motivate attempting to circumvent these limitations. 1 aChilds, Andrew, M. uhttp://arxiv.org/abs/0810.0312v301343nas a2200193 4500008004100000245007300041210006900114260001300183490000700196520075700203100001400960700002500974700002100999700002601020700002001046700002301066700002301089856003701112 2009 eng d00aRealization of Coherent Optically Dense Media via Buffer-Gas Cooling0 aRealization of Coherent Optically Dense Media via BufferGas Cool c2009/1/60 v793 a We demonstrate that buffer-gas cooling combined with laser ablation can be used to create coherent optical media with high optical depth and low Doppler broadening that offers metastable states with low collisional and motional decoherence. Demonstration of this generic technique opens pathways to coherent optics with a large variety of atoms and molecules. We use helium buffer gas to cool 87Rb atoms to below 7 K and slow atom diffusion to the walls. Electromagnetically induced transparency (EIT) in this medium allows for 50% transmission in a medium with initial OD >70 and for slow pulse propagation with large delay-bandwidth products. In the high-OD regime, we observe high-contrast spectrum oscillations due to efficient four-wave mixing. 1 aHong, Tao1 aGorshkov, Alexey, V.1 aPatterson, David1 aZibrov, Alexander, S.1 aDoyle, John, M.1 aLukin, Mikhail, D.1 aPrentiss, Mara, G. uhttp://arxiv.org/abs/0805.1416v201375nas a2200181 4500008004100000245008800041210006900129260001400198490000700212520082100219100001901040700001801059700002001077700001501097700001901112700001801131856004401149 2007 eng d00aRelaxation, dephasing, and quantum control of electron spins in double quantum dots0 aRelaxation dephasing and quantum control of electron spins in do c2007/7/130 v763 aRecent experiments have demonstrated quantum manipulation of two-electron spin states in double quantum dots using electrically controlled exchange interactions. Here, we present a detailed theory for electron spin dynamics in two-electron double dot systems that was used to guide these experiments and analyze experimental results. The theory treats both charge and spin degrees of freedom on an equal basis. Specifically, we analyze the relaxation and dephasing mechanisms that are relevant to experiments and discuss practical approaches for quantum control of two-electron system. We show that both charge and spin dephasing play important roles in the dynamics of the two-spin system, but neither represents a fundamental limit for electrical control of spin degrees of freedom in semiconductor quantum bits. 1 aTaylor, J., M.1 aPetta, J., R.1 aJohnson, A., C.1 aYacoby, A.1 aMarcus, C., M.1 aLukin, M., D. uhttp://arxiv.org/abs/cond-mat/0602470v201193nas a2200145 4500008004100000245012200041210006900163260001400232490000700246520068300253100002200936700002300958700002300981856004301004 2004 eng d00aRelativistic many-body calculations of electric-dipole matrix elements, lifetimes and polarizabilities in rubidium 0 aRelativistic manybody calculations of electricdipole matrix elem c2004/2/270 v693 a Electric-dipole matrix elements for ns-n'p, nd-n'p, and 6d-4f transitions in Rb are calculated using a relativistic all-order method. A third-order calculation is also carried out for these matrix elements to evaluate the importance of the high-order many-body perturbation theory contributions. The all-order matrix elements are used to evaluate lifetimes of ns and np levels with n=6, 7, 8 and nd levels with n=4, 5, 6 for comparison with experiment and to provide benchmark values for these lifetimes. The dynamic polarizabilities are calculated for ns states of rubidium. The resulting lifetime and polarizability values are compared with available theory and experiment. 1 aSafronova, M., S.1 aWilliams, Carl, J.1 aClark, Charles, W. uhttp://arxiv.org/abs/physics/0307057v101270nas a2200157 4500008004100000245006000041210006000101260001500161300001600176490000700192520080600199100002301005700002201028700001801050856004401068 2004 eng d00aReversible simulation of bipartite product Hamiltonians0 aReversible simulation of bipartite product Hamiltonians c2004/06/01 a1189 - 11970 v503 a Consider two quantum systems A and B interacting according to a product Hamiltonian H = H_A x H_B. We show that any two such Hamiltonians can be used to simulate each other reversibly (i.e., without efficiency losses) with the help of local unitary operations and local ancillas. Accordingly, all non-local features of a product Hamiltonian -- including the rate at which it can be used to produce entanglement, transmit classical or quantum information, or simulate other Hamiltonians -- depend only upon a single parameter. We identify this parameter and use it to obtain an explicit expression for the entanglement capacity of all product Hamiltonians. Finally, we show how the notion of simulation leads to a natural formulation of measures of the strength of a nonlocal Hamiltonian. 1 aChilds, Andrew, M.1 aLeung, Debbie, W.1 aVidal, Guifre uhttp://arxiv.org/abs/quant-ph/0303097v101006nas a2200145 4500008004100000245005300041210005300094260001400147490000700161520058100168100002300749700002200772700002200794856004400816 2001 eng d00aRealization of quantum process tomography in NMR0 aRealization of quantum process tomography in NMR c2001/6/130 v643 a Quantum process tomography is a procedure by which the unknown dynamical evolution of an open quantum system can be fully experimentally characterized. We demonstrate explicitly how this procedure can be implemented with a nuclear magnetic resonance quantum computer. This allows us to measure the fidelity of a controlled-not logic gate and to experimentally investigate the error model for our computer. Based on the latter analysis, we test an important assumption underlying nearly all models of quantum error correction, the independence of errors on different qubits. 1 aChilds, Andrew, M.1 aChuang, Isaac, L.1 aLeung, Debbie, W. uhttp://arxiv.org/abs/quant-ph/0012032v100767nas a2200145 4500008004100000245004800041210004800089260001500137490000700152520035800159100002300517700001800540700001900558856004400577 2001 eng d00aRobustness of adiabatic quantum computation0 aRobustness of adiabatic quantum computation c2001/12/140 v653 a We study the fault tolerance of quantum computation by adiabatic evolution, a quantum algorithm for solving various combinatorial search problems. We describe an inherent robustness of adiabatic computation against two kinds of errors, unitary control errors and decoherence, and we study this robustness using numerical simulations of the algorithm. 1 aChilds, Andrew, M.1 aFarhi, Edward1 aPreskill, John uhttp://arxiv.org/abs/quant-ph/0108048v100462nas a2200121 4500008004100000245007000041210006900111300001200180490000700192100001500199700001700214856010900231 1999 eng d00aRanders surfaces whose Laplacians have completely positive symbol0 aRanders surfaces whose Laplacians have completely positive symbo a27–400 v381 aBao, David1 aLackey, Brad uhttps://www.quics.umd.edu/publications/randers-surfaces-whose-laplacians-have-completely-positive-symbol00707nas a2200133 4500008004100000245010200041210006900143260001500212520024500227100001700472700001700489700002300506856004400529 1999 eng d00aRevised Proof of the Uniqueness Theorem for 'No Collapse' Interpretations of Quantum Mechanics 0 aRevised Proof of the Uniqueness Theorem for No Collapse Interpre c1999/10/223 a We show that the Bub-Clifton uniqueness theorem for 'no collapse' interpretations of quantum mechanics (Studies in the History and Philosophy of Modern Physics 27, 181-219 (1996)) can be proved without the 'weak separability' assumption. 1 aBub, Jeffrey1 aClifton, Rob1 aGoldstein, Sheldon uhttp://arxiv.org/abs/quant-ph/9910097v1