01846nas a2200337 4500008004100000245008100041210006900122260001500191520083900206100002401045700002201069700001801091700001801109700002001127700002301147700002301170700002301193700002301216700002301239700002101262700001801283700002201301700002401323700001701347700002501364700002101389700002301410700002101433700001701454856003701471 2023 eng d00aData Needs and Challenges of Quantum Dot Devices Automation: Workshop Report0 aData Needs and Challenges of Quantum Dot Devices Automation Work c12/21/20233 a

Gate-defined quantum dots are a promising candidate system to realize scalable, coupled qubit systems and serve as a fundamental building block for quantum computers. However, present-day quantum dot devices suffer from imperfections that must be accounted for, which hinders the characterization, tuning, and operation process. Moreover, with an increasing number of quantum dot qubits, the relevant parameter space grows sufficiently to make heuristic control infeasible. Thus, it is imperative that reliable and scalable autonomous tuning approaches are developed. In this report, we outline current challenges in automating quantum dot device tuning and operation with a particular focus on datasets, benchmarking, and standardization. We also present ideas put forward by the quantum dot community on how to overcome them.

1 aZwolak, Justyna, P.1 aTaylor, Jacob, M.1 aAndrews, Reed1 aBenson, Jared1 aBryant, Garnett1 aButerakos, Donovan1 aChatterjee, Anasua1 aSarma, Sankar, Das1 aEriksson, Mark, A.1 aGreplová, Eliška1 aGullans, Michael1 aHader, Fabian1 aKovach, Tyler, J.1 aMundada, Pranav, S.1 aRamsey, Mick1 aRasmussen, Torbjoern1 aSeverin, Brandon1 aSigillito, Anthony1 aUndseth, Brennan1 aWeber, Brian uhttps://arxiv.org/abs/2312.1432200422nas a2200133 4500008004100000245006200041210006100103260001400164490000800178100002400186700001900210700002200229856003700251 2023 eng d00aDecoherence from Long-Range Forces in Atom Interferometry0 aDecoherence from LongRange Forces in Atom Interferometry c3/17/20230 v1071 aKunjummen, Jonathan1 aCarney, Daniel1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2205.0300601726nas a2200253 4500008004100000022001400041245005000055210005000105260001500155490000600170520104100176100002201217700002201239700001801261700002101279700001601300700001301316700002901329700001801358700002401376700001901400700001601419856003701435 2023 eng d a2375-254800aDigital quantum simulation of NMR experiments0 aDigital quantum simulation of NMR experiments c11/29/20230 v93 a

Simulations of nuclear magnetic resonance (NMR) experiments can be an important tool for extracting information about molecular structure and optimizing experimental protocols but are often intractable on classical computers for large molecules such as proteins and for protocols such as zero-field NMR. We demonstrate the first quantum simulation of an NMR spectrum, computing the zero-field spectrum of the methyl group of acetonitrile using four qubits of a trapped-ion quantum computer. We reduce the sampling cost of the quantum simulation by an order of magnitude using compressed sensing techniques. We show how the intrinsic decoherence of NMR systems may enable the zero-field simulation of classically hard molecules on relatively near-term quantum hardware and discuss how the experimentally demonstrated quantum algorithm can be used to efficiently simulate scientifically and technologically relevant solid-state NMR experiments on more mature devices. Our work opens a practical application for quantum computation.

1 aSeetharam, Kushal1 aBiswas, Debopriyo1 aNoel, Crystal1 aRisinger, Andrew1 aZhu, Daiwei1 aKatz, Or1 aChattopadhyay, Sambuddha1 aCetina, Marko1 aMonroe, Christopher1 aDemler, Eugene1 aSels, Dries uhttps://arxiv.org/abs/2109.1329801347nas a2200145 4500008004100000245012000041210006900161260001500230520084500245100002401090700001301114700001801127700001901145856003701164 2023 eng d00aThe discrete adiabatic quantum linear system solver has lower constant factors than the randomized adiabatic solver0 adiscrete adiabatic quantum linear system solver has lower consta c12/12/20233 a

The solution of linear systems of equations is the basis of many other quantum algorithms, and recent results provided an algorithm with optimal scaling in both the condition number κ and the allowable error ϵ [PRX Quantum \textbf{3}, 0403003 (2022)]. That work was based on the discrete adiabatic theorem, and worked out an explicit constant factor for an upper bound on the complexity. Here we show via numerical testing on random matrices that the constant factor is in practice about 1,500 times smaller than the upper bound found numerically in the previous results. That means that this approach is far more efficient than might naively be expected from the upper bound. In particular, it is over an order of magnitude more efficient than using a randomised approach from [arXiv:2305.11352] that claimed to be more efficient.

1 aCosta, Pedro, C. S.1 aAn, Dong1 aBabbush, Ryan1 aBerry, Dominic uhttps://arxiv.org/abs/2312.0769001222nas a2200157 4500008004100000245006100041210006000102260001400162520073300176100003100909700001600940700002500956700001800981700002800999856003701027 2023 eng d00aDiVincenzo-like criteria for autonomous quantum machines0 aDiVincenzolike criteria for autonomous quantum machines c7/17/20233 a

Controlled quantum machines have matured significantly. A natural next step is to grant them autonomy, freeing them from timed external control. For example, autonomy could unfetter quantum computers from classical control wires that heat and decohere them; and an autonomous quantum refrigerator recently reset superconducting qubits to near their ground states, as is necessary before a computation. What conditions are necessary for realizing useful autonomous quantum machines? Inspired by recent quantum thermodynamics and chemistry, we posit conditions analogous to DiVincenzo's criteria for quantum computing. Our criteria are intended to foment and guide the development of useful autonomous quantum machines.

1 aGuzmán, José, Antonio Ma1 aErker, Paul1 aGasparinetti, Simone1 aHuber, Marcus1 aHalpern, Nicole, Yunger uhttps://arxiv.org/abs/2307.0873901358nas a2200157 4500008004100000245008900041210006900130260001500199520084100214100002501055700001801080700002001098700002101118700002401139856003701163 2022 eng d00aDark Solitons in Bose-Einstein Condensates: A Dataset for Many-body Physics Research0 aDark Solitons in BoseEinstein Condensates A Dataset for Manybody c05/17/20223 a

We establish a dataset of over 1.6×104 experimental images of Bose-Einstein condensates containing solitonic excitations to enable machine learning (ML) for many-body physics research. About 33 % of this dataset has manually assigned and carefully curated labels. The remainder is automatically labeled using SolDet -- an implementation of a physics-informed ML data analysis framework -- consisting of a convolutional-neural-network-based classifier and object detector as well as a statistically motivated physics-informed classifier and a quality metric. This technical note constitutes the definitive reference of the dataset, providing an opportunity for the data science community to develop more sophisticated analysis tools, to further understand nonlinear many-body physics, and even advance cold atom experiments.

1 aFritsch, Amilson, R.1 aGuo, Shangjie1 aKoh, Sophia, M.1 aSpielman, I., B.1 aZwolak, Justyna, P. uhttps://arxiv.org/abs/2205.0911401033nas a2200193 4500008004100000245005300041210005300094260001300147520041400160653002700574653004200601653002900643653003100672653005200703100001400755700001700769700001600786856003700802 2022 eng d00aDeconfinement and Error Thresholds in Holography0 aDeconfinement and Error Thresholds in Holography c2/9/20223 a

We study the error threshold properties of holographic quantum error-correcting codes. We demonstrate that holographic CFTs admit an algebraic threshold, which is related to the confinement-deconfinement phase transition. We then apply geometric intuition from holography and the Hawking-Page phase transition to motivate the CFT result, and comment on potential extensions to other confining theories.

10aFOS: Physical sciences10aHigh Energy Physics - Theory (hep-th)10aNuclear Theory (nucl-th)10aQuantum Physics (quant-ph)10aStrongly Correlated Electrons (cond-mat.str-el)1 aBao, Ning1 aCao, Charles1 aZhu, Guanyu uhttps://arxiv.org/abs/2202.0471001214nas a2200193 4500008004100000245008100041210006900122260001400191520059300205653003700798653002700835653003100862100001300893700001400906700002100920700002400941700001800965856003700983 2022 eng d00aDemonstration of three- and four-body interactions between trapped-ion spins0 aDemonstration of three and fourbody interactions between trapped c9/12/20223 a

Quantum processors use the native interactions between effective spins to simulate Hamiltonians or execute quantum gates. In most processors, the native interactions are pairwise, limiting the efficiency of controlling entanglement between many qubits. Here we experimentally demonstrate a new class of native interactions between trapped-ion qubits, extending conventional pairwise interactions to higher order. We realize three- and four-body spin interactions as examples, showing that high-order spin polynomials may serve as a new toolbox for quantum information applications.

10aAtomic Physics (physics.atom-ph)10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aKatz, Or1 aFeng, Lei1 aRisinger, Andrew1 aMonroe, Christopher1 aCetina, Marko uhttps://arxiv.org/abs/2209.0569101903nas a2200193 4500008004100000245006000041210006000101260001400161520128300175653004301458653002701501653002901528653003401557653003101591100001501622700002001637700001501657856003701672 2022 eng d00aDifferentiable Quantum Programming with Unbounded Loops0 aDifferentiable Quantum Programming with Unbounded Loops c11/8/20223 a

The emergence of variational quantum applications has led to the development of automatic differentiation techniques in quantum computing. Recently, Zhu et al. (PLDI 2020) have formulated differentiable quantum programming with bounded loops, providing a framework for scalable gradient calculation by quantum means for training quantum variational applications. However, promising parameterized quantum applications, e.g., quantum walk and unitary implementation, cannot be trained in the existing framework due to the natural involvement of unbounded loops. To fill in the gap, we provide the first differentiable quantum programming framework with unbounded loops, including a newly designed differentiation rule, code transformation, and their correctness proof. Technically, we introduce a randomized estimator for derivatives to deal with the infinite sum in the differentiation of unbounded loops, whose applicability in classical and probabilistic programming is also discussed. We implement our framework with Python and Q#, and demonstrate a reasonable sample efficiency. Through extensive case studies, we showcase an exciting application of our framework in automatically identifying close-to-optimal parameters for several parameterized quantum applications.

10aFOS: Computer and information sciences10aFOS: Physical sciences10aMachine Learning (cs.LG)10aProgramming Languages (cs.PL)10aQuantum Physics (quant-ph)1 aFang, Wang1 aYing, Mingsheng1 aWu, Xiaodi uhttps://arxiv.org/abs/2211.0450701894nas a2200193 4500008004100000245005300041210005200094260001400146520125500160653006101415653002701476653003501503653003101538100002901569700002001598700002001618700002501638856003701663 2022 eng d00aDisordered Lieb-Robinson bounds in one dimension0 aDisordered LiebRobinson bounds in one dimension c8/10/20223 a

By tightening the conventional Lieb-Robinson bounds to better handle systems which lack translation invariance, we determine the extent to which "weak links" suppress operator growth in disordered one-dimensional spin chains. In particular, we prove that ballistic growth is impossible when the distribution of coupling strengths μ(J) has a sufficiently heavy tail at small J, and identify the correct dynamical exponent to use instead. Furthermore, through a detailed analysis of the special case in which the couplings are genuinely random and independent, we find that the standard formulation of Lieb-Robinson bounds is insufficient to capture the complexity of the dynamics -- we must distinguish between bounds which hold for all sites of the chain and bounds which hold for a subsequence of sites, and we show by explicit example that these two can have dramatically different behaviors. All the same, our result for the dynamical exponent is tight, in that we prove by counterexample that there cannot exist any Lieb-Robinson bound with a smaller exponent. We close by discussing the implications of our results, both major and minor, for numerous applications ranging from quench dynamics to the structure of ground states.

10aDisordered Systems and Neural Networks (cond-mat.dis-nn)10aFOS: Physical sciences10aMathematical Physics (math-ph)10aQuantum Physics (quant-ph)1 aBaldwin, Christopher, L.1 aEhrenberg, Adam1 aGuo, Andrew, Y.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2208.0550901900nas a2200157 4500008004100000245008000041210006900121260001400190520140900204100001601613700001801629700001801647700001901665700002101684856003701705 2021 eng d00aDecoding conformal field theories: from supervised to unsupervised learning0 aDecoding conformal field theories from supervised to unsupervise c7/10/20213 a

We use machine learning to classify rational two-dimensional conformal field theories. We first use the energy spectra of these minimal models to train a supervised learning algorithm. We find that the machine is able to correctly predict the nature and the value of critical points of several strongly correlated spin models using only their energy spectra. This is in contrast to previous works that use machine learning to classify different phases of matter, but do not reveal the nature of the critical point between phases. Given that the ground-state entanglement Hamiltonian of certain topological phases of matter is also described by conformal field theories, we use supervised learning on Réyni entropies and find that the machine is able to identify which conformal field theory describes the entanglement Hamiltonian with only the lowest few Réyni entropies to a high degree of accuracy. Finally, using autoencoders, an unsupervised learning algorithm, we find a hidden variable that has a direct correlation with the central charge and discuss prospects for using machine learning to investigate other conformal field theories, including higher-dimensional ones. Our results highlight that machine learning can be used to find and characterize critical points and also hint at the intriguing possibility to use machine learning to learn about more complex conformal field theories.

1 aKuo, En-Jui1 aSeif, Alireza1 aLundgren, Rex1 aWhitsitt, Seth1 aHafezi, Mohammad uhttps://arxiv.org/abs/2106.1348502078nas a2200277 4500008004100000245006700041210006600108260001500174520125200189100002201441700001801463700002501481700002101506700002401527700002501551700002101576700002001597700002501617700002601642700001601668700001901684700002301703700001801726700001901744856003701763 2021 eng d00aDevice-independent Randomness Expansion with Entangled Photons0 aDeviceindependent Randomness Expansion with Entangled Photons c01/28/20213 a

With the growing availability of experimental loophole-free Bell tests, it has become possible to implement a new class of device-independent random number generators whose output can be certified to be uniformly random without requiring a detailed model of the quantum devices used. However, all of these experiments require many input bits in order to certify a small number of output bits, and it is an outstanding challenge to develop a system that generates more randomness than is used. Here, we devise a device-independent spot-checking protocol which uses only uniform bits as input. Implemented with a photonic loophole-free Bell test, we can produce 24% more certified output bits (1,181,264,237) than consumed input bits (953,301,640), which is 5 orders of magnitude more efficient than our previous work [arXiv:1812.07786]. The experiment ran for 91.0 hours, creating randomness at an average rate of 3606 bits/s with a soundness error bounded by 5.7×10−7 in the presence of classical side information. Our system will allow for greater trust in public sources of randomness, such as randomness beacons, and the protocols may one day enable high-quality sources of private randomness as the device footprint shrinks.

1 aShalm, Lynden, K.1 aZhang, Yanbao1 aBienfang, Joshua, C.1 aSchlager, Collin1 aStevens, Martin, J.1 aMazurek, Michael, D.1 aAbellán, Carlos1 aAmaya, Waldimar1 aMitchell, Morgan, W.1 aAlhejji, Mohammad, A.1 aFu, Honghao1 aOrnstein, Joel1 aMirin, Richard, P.1 aNam, Sae, Woo1 aKnill, Emanuel uhttps://arxiv.org/abs/1912.1115801944nas a2200181 4500008004100000245006800041210006700109260001400176520137900190100002201569700001801591700001801609700002401627700002801651700002101679700002501700856003701725 2021 eng d00aDiscovering hydrodynamic equations of many-body quantum systems0 aDiscovering hydrodynamic equations of manybody quantum systems c11/3/20213 a

Simulating and predicting dynamics of quantum many-body systems is extremely challenging, even for state-of-the-art computational methods, due to the spread of entanglement across the system. However, in the long-wavelength limit, quantum systems often admit a simplified description, which involves a small set of physical observables and requires only a few parameters such as sound velocity or viscosity. Unveiling the relationship between these hydrodynamic equations and the underlying microscopic theory usually requires a great effort by condensed matter theorists. In the present paper, we develop a new machine-learning framework for automated discovery of effective equations from a limited set of available data, thus bypassing complicated analytical derivations. The data can be generated from numerical simulations or come from experimental quantum simulator platforms. Using integrable models, where direct comparisons can be made, we reproduce previously known hydrodynamic equations, strikingly discover novel equations and provide their derivation whenever possible. We discover new hydrodynamic equations describing dynamics of interacting systems, for which the derivation remains an outstanding challenge. Our approach provides a new interpretable method to study properties of quantum materials and quantum simulators in non-perturbative regimes.

1 aKharkov, Yaroslav1 aShtanko, Oles1 aSeif, Alireza1 aBienias, Przemyslaw1 aVan Regemortel, Mathias1 aHafezi, Mohammad1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2111.0238501561nas a2200169 4500008004100000245007300041210006900114260001300183490000800196520105300204100001901257700001701276700001301293700002301306700002501329856003701354 2020 eng d00aDestructive Error Interference in Product-Formula Lattice Simulation0 aDestructive Error Interference in ProductFormula Lattice Simulat c6/4/20200 v1243 a

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

1 aTran, Minh, C.1 aChu, Su-Kuan1 aSu, Yuan1 aChilds, Andrew, M.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1912.1104701563nas a2200169 4500008004100000245002700041210002700068260001400095300001200109490000700121520114400128100002201272700002401294700001801318700002001336856003701356 2020 eng d00aDiscrete Time Crystals0 aDiscrete Time Crystals c3/10/2020 a467-4990 v113 a

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

1 aElse, Dominic, V.1 aMonroe, Christopher1 aNayak, Chetan1 aYao, Norman, Y. uhttps://arxiv.org/abs/1905.1323201603nas a2200145 4500008004100000245010500041210006900146260001400215520111300229100002901342700001501371700001901386700001501405856003701420 2020 eng d00aDistinct Critical Behaviors from the Same State in Quantum Spin and Population Dynamics Perspectives0 aDistinct Critical Behaviors from the Same State in Quantum Spin  c9/10/20203 a

There is a deep connection between the ground states of transverse-field spin systems and the late-time distributions of evolving viral populations -- within simple models, both are obtained from the principal eigenvector of the same matrix. However, that vector is the wavefunction amplitude in the quantum spin model, whereas it is the probability itself in the population model. We show that this seemingly minor difference has significant consequences: phase transitions which are discontinuous in the spin system become continuous when viewed through the population perspective, and transitions which are continuous become governed by new critical exponents. We introduce a more general class of models which encompasses both cases, and that can be solved exactly in a mean-field limit. Numerical results are also presented for a number of one-dimensional chains with power-law interactions. We see that well-worn spin models of quantum statistical mechanics can contain unexpected new physics and insights when treated as population-dynamical models and beyond, motivating further studies. 

1 aBaldwin, Christopher, L.1 aShivam, S.1 aSondhi, S., L.1 aKardar, M. uhttps://arxiv.org/abs/2009.0506401482nas a2200145 4500008004100000245005500041210005500096260001500151300000900166490000700175520108100182100001901263700001701282856003701299 2020 eng d00aDistributional property testing in a quantum world0 aDistributional property testing in a quantum world c02/02/2019 a1-250 v253 a

A fundamental problem in statistics and learning theory is to test properties of distributions. We show that quantum computers can solve such problems with significant speed-ups. In particular, we give fast quantum algorithms for testing closeness between unknown distributions, testing independence between two distributions, and estimating the Shannon / von Neumann entropy of distributions. The distributions can be either classical or quantum, however our quantum algorithms require coherent quantum access to a process preparing the samples. Our results build on the recent technique of quantum singular value transformation, combined with more standard tricks such as divide-and-conquer. The presented approach is a natural fit for distributional property testing both in the classical and the quantum case, demonstrating the first speed-ups for testing properties of density operators that can be accessed coherently rather than only via sampling; for classical distributions our algorithms significantly improve the precision dependence of some earlier results.

1 aGilyen, Andras1 aLi, Tongyang uhttps://arxiv.org/abs/1902.0081402342nas a2200133 4500008004100000245007600041210006900117260001400186490000700200520192300207100002102130700002002151856003702171 2020 eng d00aDynamical Purification Phase Transition Induced by Quantum Measurements0 aDynamical Purification Phase Transition Induced by Quantum Measu c7/30/20200 v103 a

Continuously monitoring the environment of a quantum many-body system reduces the entropy of (purifies) the reduced density matrix of the system, conditional on the outcomes of the measurements. We show that, for mixed initial states, a balanced competition between measurements and entangling interactions within the system can result in a dynamical purification phase transition between (i) a phase that locally purifies at a constant system-size-independent rate, and (ii) a "mixed" phase where the purification time diverges exponentially in the system size. The residual entropy density in the mixed phase implies the existence of a quantum error-protected subspace where quantum information is reliably encoded against the future non-unitary evolution of the system. We show that these codes are of potential relevance to fault-tolerant quantum computation as they are often highly degenerate and satisfy optimal tradeoffs between encoded information densities and error thresholds. In spatially local models in 1+1 dimensions, this phase transition for mixed initial states occurs concurrently with a recently identified class of entanglement phase transitions for pure initial states. The mutual information of an initially completely-mixed state in 1+1 dimensions grows sublinearly in time due to the formation of the error protected subspace. The purification transition studied here also generalizes to systems with long-range interactions, where conventional notions of entanglement transitions have to be reformulated. Purification dynamics is likely a more robust probe of the transition in experiments, where imperfections generically reduce entanglement and drive the system towards mixed states. We describe the motivations for studying this novel class of non-equilibrium quantum dynamics in the context of advanced quantum computing platforms and fault-tolerant quantum computation.

1 aGullans, Michael1 aHuse, David, A. uhttps://arxiv.org/abs/1905.0519502955nas a2200397 4500008004100000245008600041210006900127260001500196520181200211100002102023700002302044700002002067700001702087700002202104700001702126700002502143700001802168700001902186700001702205700001702222700002702239700001502266700001702281700001802298700001702316700001602333700002002349700001902369700002302388700002502411700002402436700001802460700002002478700002202498856003702520 2019 eng d00aDevelopment of Quantum InterConnects for Next-Generation Information Technologies0 aDevelopment of Quantum InterConnects for NextGeneration Informat c12/13/20193 a

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

1 aAwschalom, David1 aBerggren, Karl, K.1 aBernien, Hannes1 aBhave, Sunil1 aCarr, Lincoln, D.1 aDavids, Paul1 aEconomou, Sophia, E.1 aEnglund, Dirk1 aFaraon, Andrei1 aFejer, Marty1 aGuha, Saikat1 aGustafsson, Martin, V.1 aHu, Evelyn1 aJiang, Liang1 aKim, Jungsang1 aKorzh, Boris1 aKumar, Prem1 aKwiat, Paul, G.1 aLončar, Marko1 aLukin, Mikhail, D.1 aMiller, David, A. B.1 aMonroe, Christopher1 aNam, Sae, Woo1 aNarang, Prineha1 aOrcutt, Jason, S. uhttps://arxiv.org/abs/1912.0664204213nas a2200241 4500008004100000245006900041210006800110260001500178300001100193490000800204520348600212100001503698700002303713700002403736700001903760700001903779700002503798700002503823700001803848700002103866700002403887856006003911 2018 eng d00aDark state optical lattice with sub-wavelength spatial structure0 aDark state optical lattice with subwavelength spatial structure c2018/02/20 a0836010 v1203 a

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

1 aWang, Yang1 aSubhankar, Sarthak1 aBienias, Przemyslaw1 aLacki, Mateusz1 aTsui, Tsz-Chun1 aBaranov, Mikhail, A.1 aGorshkov, Alexey, V.1 aZoller, Peter1 aPorto, James, V.1 aRolston, Steven, L. uhttps://link.aps.org/doi/10.1103/PhysRevLett.120.08360101552nas a2200169 4500008004100000245007500041210006900116520100400185100001901189700002301208700002201231700002401253700002401277700002001301700002401321856003701345 2018 eng d00aDemonstration of Bayesian quantum game on an ion trap quantum computer0 aDemonstration of Bayesian quantum game on an ion trap quantum co3 a

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

1 aSolmeyer, Neal1 aLinke, Norbert, M.1 aFiggatt, Caroline1 aLandsman, Kevin, A.1 aBalu, Radhakrishnan1 aSiopsis, George1 aMonroe, Christopher uhttps://arxiv.org/abs/1802.0811601752nas a2200169 4500008004100000245007800041210006900119260001500188300001100203490000700214520121000221100002201431700002101453700002401474700001501498856006901513 2018 eng d00aDiffusion Monte Carlo Versus Adiabatic Computation for Local Hamiltonians0 aDiffusion Monte Carlo Versus Adiabatic Computation for Local Ham c2018/02/15 a0223230 v973 a

Most research regarding quantum adiabatic optimization has focused on stoquastic Hamiltonians, whose ground states can be expressed with only real, nonnegative amplitudes. This raises the question of whether classical Monte Carlo algorithms can efficiently simulate quantum adiabatic optimization with stoquastic Hamiltonians. Recent results have given counterexamples in which path integral and diffusion Monte Carlo fail to do so. However, most adiabatic optimization algorithms, such as for solving MAX-k-SAT problems, use k-local Hamiltonians, whereas our previous counterexample for diffusion Monte Carlo involved n-body interactions. Here we present a new 6-local counterexample which demonstrates that even for these local Hamiltonians there are cases where diffusion Monte Carlo cannot efficiently simulate quantum adiabatic optimization. Furthermore, we perform empirical testing of diffusion Monte Carlo on a standard well-studied class of permutation-symmetric tunneling problems and similarly find large advantages for quantum optimization over diffusion Monte Carlo.

1 aBringewatt, Jacob1 aDorland, William1 aJordan, Stephen, P.1 aMink, Alan uhttps://journals.aps.org/pra/abstract/10.1103/PhysRevA.97.02232303349nas a2200217 4500008004100000245008400041210006900125260001500194300001100209490000700220520266700227100002202894700002002916700001702936700003102953700002102984700002403005700002103029700002503050856005603075 2018 eng d00aDissipation induced dipole blockade and anti-blockade in driven Rydberg systems0 aDissipation induced dipole blockade and antiblockade in driven R c2018/02/28 a0234240 v973 a

We study theoretically and experimentally the competing blockade and antiblockade effects induced by spontaneously generated contaminant Rydberg atoms in driven Rydberg systems. These contaminant atoms provide a source of strong dipole-dipole interactions and play a crucial role in the system's behavior. We study this problem theoretically using two different approaches. The first is a cumulant expansion approximation, in which we ignore third-order and higher connected correlations. Using this approach for the case of resonant drive, a many-body blockade radius picture arises, and we find qualitative agreement with previous experimental results. We further predict that as the atomic density is increased, the Rydberg population's dependence on Rabi frequency will transition from quadratic to linear dependence at lower Rabi frequencies. We study this behavior experimentally by observing this crossover at two different atomic densities. We confirm that the larger density system has a smaller crossover Rabi frequency than the smaller density system. The second theoretical approach is a set of phenomenological inhomogeneous rate equations. We compare the results of our rate-equation model to the experimental observations [E. A. Goldschmidt et al.Phys. Rev. Lett. 116, 113001 (2016)] and find that these rate equations provide quantitatively good scaling behavior of the steady-state Rydberg population for both resonant and off-resonant drives.

1 aYoung, Jeremy, T.1 aBoulier, Thomas1 aMagnan, Eric1 aGoldschmidt, Elizabeth, A.1 aWilson, Ryan, M.1 aRolston, Steven, L.1 aPorto, James, V.1 aGorshkov, Alexey, V. uhttps://link.aps.org/doi/10.1103/PhysRevA.97.02342401538nas a2200157 4500008004100000245007800041210006900119260001500188520103700203100001601240700001701256700002201273700002501295700002301320856003701343 2018 eng d00aDistributed Quantum Metrology and the Entangling Power of Linear Networks0 aDistributed Quantum Metrology and the Entangling Power of Linear c2018/07/253 a

We derive a bound on the ability of a linear optical network to estimate a linear combination of independent phase shifts by using an arbitrary non-classical but unentangled input state, thereby elucidating the quantum resources required to obtain the Heisenberg limit with a multi-port interferometer. Our bound reveals that while linear networks can generate highly entangled states, they cannot effectively combine quantum resources that are well distributed across multiple modes for the purposes of metrology: in this sense linear networks endowed with well-distributed quantum resources behave classically. Conversely, our bound shows that linear networks can achieve the Heisenberg limit for distributed metrology when the input photons are hoarded in a small number of input modes, and we present an explicit scheme for doing so. Our results also have implications for measures of non-classicality.

1 aGe, Wenchao1 aJacobs, Kurt1 aEldredge, Zachary1 aGorshkov, Alexey, V.1 aFoss-Feig, Michael uhttps://arxiv.org/abs/1707.0665501425nas a2200157 4500008004100000245007800041210006900119260001500188520092400203100001601127700001701143700002201160700002501182700002301207856003701230 2018 eng d00aDistributed Quantum Metrology and the Entangling Power of Linear Networks0 aDistributed Quantum Metrology and the Entangling Power of Linear c2018/07/253 a

We derive a bound on the ability of a linear optical network to estimate a linear combination of independent phase shifts by using an arbitrary non-classical but unentangled input state, thereby elucidating the quantum resources required to obtain the Heisenberg limit with a multi-port interferometer. Our bound reveals that while linear networks can generate highly entangled states, they cannot effectively combine quantum resources that are well distributed across multiple modes for the purposes of metrology: in this sense linear networks endowed with well-distributed quantum resources behave classically. Conversely, our bound shows that linear networks can achieve the Heisenberg limit for distributed metrology when the input photons are hoarded in a small number of input modes, and we present an explicit scheme for doing so. Our results also have implications for measures of non-classicality. 

1 aGe, Wenchao1 aJacobs, Kurt1 aEldredge, Zachary1 aGorshkov, Alexey, V.1 aFoss-Feig, Michael uhttps://arxiv.org/abs/1707.0665501943nas a2200121 4500008004100000245007800041210006900119520154200188100001801730700001901748700001701767856003701784 2018 eng d00aDynamic suppression of Rayleigh light scattering in dielectric resonators0 aDynamic suppression of Rayleigh light scattering in dielectric r3 a

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

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

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

1 aDeshpande, Abhinav1 aFefferman, Bill1 aTran, Minh, C.1 aFoss-Feig, Michael1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1703.0533201586nas a2200193 4500008004100000245007900041210006900120260001400189490000700203520099200210100002401202700002201226700002201248700001901270700002001289700002701309700001901336856003701355 2017 eng d00aDevelopment of a new UHV/XHV pressure standard (cold atom vacuum standard)0 aDevelopment of a new UHVXHV pressure standard cold atom vacuum s c2017/11/30 v543 a

The National Institute of Standards and Technology has recently begun a program to develop a primary pressure standard that is based on ultra-cold atoms, covering a pressure range of 1 x 10-6 to 1 x 10-10 Pa and possibly lower. These pressures correspond to the entire ultra-high vacuum range and extend into the extreme-high vacuum. This cold-atom vacuum standard (CAVS) is both a primary standard and absolute sensor of vacuum. The CAVS is based on the loss of cold, sensor atoms (such as the alkali-metal lithium) from a magnetic trap due to collisions with the background gas (primarily H2) in the vacuum. The pressure is determined from a thermally-averaged collision cross section, which is a fundamental atomic property, and the measured loss rate. The CAVS is primary because it will use collision cross sections determined from ab initio calculations for the Li + H2 system. Primary traceability is transferred to other systems of interest using sensitivity coefficients.

1 aScherschligt, Julia1 aFedchak, James, A1 aBarker, Daniel, S1 aEckel, Stephen1 aKlimov, Nikolai1 aMakrides, Constantinos1 aTiesinga, Eite uhttps://arxiv.org/abs/1801.1012001465nas a2200157 4500008004100000245008500041210006900126260001500195300001100210490000700221520098400228100001701212700002501229700001601254856003701270 2017 eng d00aDisorder induced transitions in resonantly driven Floquet Topological Insulators0 aDisorder induced transitions in resonantly driven Floquet Topolo c2017/08/16 a0542070 v963 a

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

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

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

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

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

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

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

1 aKim, Seunghwi1 aXu, Xunnong1 aTaylor, J., M.1 aBahl, Gaurav uhttps://arxiv.org/abs/1609.0867402040nas a2200193 4500008004100000245007800041210006900119260001500188300001000203490000800213520145000221100001601671700001801687700001601705700002101721700001501742700001501757856007401772 2016 eng d00aDemonstration of a small programmable quantum computer with atomic qubits0 aDemonstration of a small programmable quantum computer with atom c2016/08/04 a63-660 v5363 a

Quantum computers can solve certain problems more efficiently than any possible conventional computer. Small quantum algorithms have been demonstrated on multiple quantum computing platforms, many specifically tailored in hardware to implement a particular algorithm or execute a limited number of computational paths. Here, we demonstrate a five-qubit trapped-ion quantum computer that can be programmed in software to implement arbitrary quantum algorithms by executing any sequence of universal quantum logic gates. We compile algorithms into a fully-connected set of gate operations that are native to the hardware and have a mean fidelity of 98 %. Reconfiguring these gate sequences provides the flexibility to implement a variety of algorithms without altering the hardware. As examples, we implement the Deutsch-Jozsa (DJ) and Bernstein-Vazirani (BV) algorithms with average success rates of 95 % and 90 %, respectively. We also perform a coherent quantum Fourier transform (QFT) on five trappedion qubits for phase estimation and period finding with average fidelities of 62 % and 84 %, respectively. This small quantum computer can be scaled to larger numbers of qubits within a single register, and can be further expanded by connecting several such modules through ion shuttling or photonic quantum channels.

1 aDebnath, S.1 aLinke, N., M.1 aFiggatt, C.1 aLandsman, K., A.1 aWright, K.1 aMonroe, C. uhttp://www.nature.com/nature/journal/v536/n7614/full/nature18648.html01164nas a2200169 4500008004100000245007500041210006900116260001500185300001100200490000700211520067400218100001800892700001800910700001600928700001400944856003600958 2016 eng d00aDetecting Consistency of Overlapping Quantum Marginals by Separability0 aDetecting Consistency of Overlapping Quantum Marginals by Separa c2016/03/03 a0321050 v933 a The quantum marginal problem asks whether a set of given density matrices are consistent, i.e., whether they can be the reduced density matrices of a global quantum state. Not many non-trivial analytic necessary (or sufficient) conditions are known for the problem in general. We propose a method to detect consistency of overlapping quantum marginals by considering the separability of some derived states. Our method works well for the $k$-symmetric extension problem in general, and for the general overlapping marginal problems in some cases. Our work is, in some sense, the converse to the well-known $k$-symmetric extension criterion for separability. 1 aChen, Jianxin1 aJi, Zhengfeng1 aYu, Nengkun1 aZeng, Bei uhttp://arxiv.org/abs/1509.0659101662nas a2200217 4500008004100000245004300041210004300084260001500127300001100142490000600153520108300159100001601242700001501258700001601273700001901289700001101308700002101319700001901340700001801359856006701377 2016 eng d00aDouble Quantum Dot Floquet Gain Medium0 aDouble Quantum Dot Floquet Gain Medium c2016/11/07 a0410270 v63 a

Strongly driving a two-level quantum system with light leads to a ladder of Floquet states separated by the photon energy. Nanoscale quantum devices allow the interplay of confined electrons, phonons, and photons to be studied under strong driving conditions. Here we show that a single electron in a periodically driven DQD functions as a "Floquet gain medium," where population imbalances in the DQD Floquet quasi-energy levels lead to an intricate pattern of gain and loss features in the cavity response. We further measure a large intra-cavity photon number n_c in the absence of a cavity drive field, due to equilibration in the Floquet picture. Our device operates in the absence of a dc current -- one and the same electron is repeatedly driven to the excited state to generate population inversion. These results pave the way to future studies of non-classical light and thermalization of driven quantum systems.

1 aStehlik, J.1 aLiu, Y.-Y.1 aEichler, C.1 aHartke, T., R.1 aMi, X.1 aGullans, Michael1 aTaylor, J., M.1 aPetta, J., R. uhttp://journals.aps.org/prx/abstract/10.1103/PhysRevX.6.04102701589nas a2200193 4500008004100000245008100041210006900122260001500191300001100206490000700217520100800224100002301232700002501255700001901280700001901299700002001318700002101338856003601359 2015 eng d00aDemonstration of Robust Quantum Gate Tomography via Randomized Benchmarking0 aDemonstration of Robust Quantum Gate Tomography via Randomized B c2015/11/05 a1130190 v173 a Typical quantum gate tomography protocols struggle with a self-consistency problem: the gate operation cannot be reconstructed without knowledge of the initial state and final measurement, but such knowledge cannot be obtained without well-characterized gates. A recently proposed technique, known as randomized benchmarking tomography (RBT), sidesteps this self-consistency problem by designing experiments to be insensitive to preparation and measurement imperfections. We implement this proposal in a superconducting qubit system, using a number of experimental improvements including implementing each of the elements of the Clifford group in single `atomic' pulses and custom control hardware to enable large overhead protocols. We show a robust reconstruction of several single-qubit quantum gates, including a unitary outside the Clifford group. We demonstrate that RBT yields physical gate reconstructions that are consistent with fidelities obtained by randomized benchmarking. 1 aJohnson, Blake, R.1 ada Silva, Marcus, P.1 aRyan, Colm, A.1 aKimmel, Shelby1 aChow, Jerry, M.1 aOhki, Thomas, A. uhttp://arxiv.org/abs/1505.0668601250nas a2200217 4500008004100000245007700041210006900118260001500187300001100202490000700213520064200220100001800862700001800880700001800898700001900916700001300935700001600948700001400964700001700978856003700995 2015 eng d00aDiscontinuity of Maximum Entropy Inference and Quantum Phase Transitions0 aDiscontinuity of Maximum Entropy Inference and Quantum Phase Tra c2015/08/10 a0830190 v173 a In this paper, we discuss the connection between two genuinely quantum phenomena --- the discontinuity of quantum maximum entropy inference and quantum phase transitions at zero temperature. It is shown that the discontinuity of the maximum entropy inference of local observable measurements signals the non-local type of transitions, where local density matrices of the ground state change smoothly at the transition point. We then propose to use the quantum conditional mutual information of the ground state as an indicator to detect the discontinuity and the non-local type of quantum phase transitions in the thermodynamic limit. 1 aChen, Jianxin1 aJi, Zhengfeng1 aLi, Chi-Kwong1 aPoon, Yiu-Tung1 aShen, Yi1 aYu, Nengkun1 aZeng, Bei1 aZhou, Duanlu uhttp://arxiv.org/abs/1406.5046v201211nas a2200145 4500008004100000245006900041210006900110260001500179490000700194520077300201100001800974700001800992700001801010856003701028 2015 eng d00aDriving Rabi oscillations at the giant dipole resonance in xenon0 aDriving Rabi oscillations at the giant dipole resonance in xenon c11/23/20150 v923 a

Free-electron lasers (FELs) produce short and very intense light pulses in the XUV and x-ray regimes. We investigate the possibility to drive Rabi oscillations in xenon with an intense FEL pulse by using the unusually large dipole strength of the giant-dipole resonance (GDR). The GDR decays within less than 30 as due to its position, which is above the 4d ionization threshold. We find that intensities around 1018 W/cm2 are required to induce Rabi oscillations with a period comparable to the lifetime. The pulse duration should not exceed 100 as because xenon will be fully ionized within a few lifetimes. Rabi oscillations reveal themselves also in the photoelectron spectrum in form of Autler-Townes splittings extending over several tens of electronvolt.

1 aPabst, Stefan1 aWang, Daochen1 aSantra, Robin uhttps://arxiv.org/abs/1511.0005801142nas a2200157 4500008004100000245008300041210006900124260001500193520063900208100002300847700001800870700002400888700001900912700001600931856003700947 2014 eng d00aDifferent Strategies for Optimization Using the Quantum Adiabatic Algorithm 0 aDifferent Strategies for Optimization Using the Quantum Adiabati c2014/01/283 a We present the results of a numerical study, with 20 qubits, of the performance of the Quantum Adiabatic Algorithm on randomly generated instances of MAX 2-SAT with a unique assignment that maximizes the number of satisfied clauses. The probability of obtaining this assignment at the end of the quantum evolution measures the success of the algorithm. Here we report three strategies which consistently increase the success probability for the hardest instances in our ensemble: decreasing the overall evolution time, initializing the system in excited states, and adding a random local Hamiltonian to the middle of the evolution. 1 aCrosson, Elizabeth1 aFarhi, Edward1 aLin, Cedric, Yen-Yu1 aLin, Han-Hsuan1 aShor, Peter uhttp://arxiv.org/abs/1401.7320v101375nas a2200193 4500008004100000245007300041210006900114260002600183300000700209490000600216520073500222100002000957700001900977700001900996700001701015700002501032700001501057856010901072 2014 eng d00aDiscrete optimization using quantum annealing on sparse Ising models0 aDiscrete optimization using quantum annealing on sparse Ising mo bFrontiersc2014/09/01 a560 v23 aThis paper discusses techniques for solving discrete optimization problems using quantum annealing. Practical issues likely to affect the computation include precision limitations, finite temperature, bounded energy range, sparse connectivity, and small numbers of qubits. To address these concerns we propose a way of finding energy representations with large classical gaps between ground and first excited states, efficient algorithms for mapping non-compatible Ising models into the hardware, and the use of decomposition methods for problems that are too large to fit in hardware. We validate the approach by describing experiments with D-Wave quantum hardware for low density parity check decoding with up to 1000 variables.1 aBian, Zhengbing1 aChudak, Fabian1 aIsrael, Robert1 aLackey, Brad1 aMacready, William, G1 aRoy, Aidan uhttps://www.quics.umd.edu/publications/discrete-optimization-using-quantum-annealing-sparse-ising-models01151nas a2200145 4500008004100000245005800041210005700099260001300156490000800169520073200177100002500909700001700934700001700951856003700968 2013 eng d00aDissipative Many-body Quantum Optics in Rydberg Media0 aDissipative Manybody Quantum Optics in Rydberg Media c2013/4/90 v1103 a We develop a theoretical framework for the dissipative propagation of quantized light in interacting optical media under conditions of electromagnetically induced transparency (EIT). The theory allows us to determine the peculiar spatiotemporal structure of the output of two complementary Rydberg-EIT-based light-processing modules: the recently demonstrated single-photon filter and the recently proposed single-photon subtractor, which, respectively, let through and absorb a single photon. In addition to being crucial for applications of these and other optical quantum devices, the theory opens the door to the study of exotic dissipative many-body dynamics of strongly interacting photons in nonlinear nonlocal media. 1 aGorshkov, Alexey, V.1 aNath, Rejish1 aPohl, Thomas uhttp://arxiv.org/abs/1211.7060v102138nas a2200181 4500008004100000245011400041210006900155260001500224300001100239490000700250520155000257100002301807700002401830700002301854700002001877700002201897856003701919 2013 eng d00aDynamical quantum correlations of Ising models on an arbitrary lattice and their resilience to decoherence 0 aDynamical quantum correlations of Ising models on an arbitrary l c2013/11/07 a1130080 v153 a Ising models, and the physical systems described by them, play a central role in generating entangled states for use in quantum metrology and quantum information. In particular, ultracold atomic gases, trapped ion systems, and Rydberg atoms realize long-ranged Ising models, which even in the absence of a transverse field can give rise to highly non-classical dynamics and long-range quantum correlations. In the first part of this paper, we present a detailed theoretical framework for studying the dynamics of such systems driven (at time t=0) into arbitrary unentangled non-equilibrium states, thus greatly extending and unifying the work of Ref. [1]. Specifically, we derive exact expressions for closed-time-path ordered correlation functions, and use these to study experimentally relevant observables, e.g. Bloch vector and spin-squeezing dynamics. In the second part, these correlation functions are then used to derive closed-form expressions for the dynamics of arbitrary spin-spin correlation functions in the presence of both T_1 (spontaneous spin relaxation/excitation) and T_2 (dephasing) type decoherence processes. Even though the decoherence is local, our solution reveals that the competition between Ising dynamics and T_1 decoherence gives rise to an emergent non-local dephasing effect, thereby drastically amplifying the degradation of quantum correlations. In addition to identifying the mechanism of this deleterious effect, our solution points toward a scheme to eliminate it via measurement-based coherent feedback. 1 aFoss-Feig, Michael1 aHazzard, Kaden, R A1 aBollinger, John, J1 aRey, Ana, Maria1 aClark, Charles, W uhttp://arxiv.org/abs/1306.0172v103224nas a2200205 4500008004100000022001400041245009700055210006900152260001500221300001400236490000700250520257700257653002302834653002602857653002802883100002002911700001702931700001602948856005402964 2011 eng d a1533-714600aDeciding Unitary Equivalence Between Matrix Polynomials and Sets of Bipartite Quantum States0 aDeciding Unitary Equivalence Between Matrix Polynomials and Sets c2001/09/01 a813–8190 v113 a

In this brief report, we consider the equivalence between two sets of m + 1 bipartite quantum states under local unitary transformations. For pure states, this problem corresponds to the matrix algebra question of whether two degree m matrix polynomials are unitarily equivalent; i.e. UAiV† = Bi for 0 ≤ i ≤ m where U and V are unitary and (Ai, Bi) are arbitrary pairs of rectangular matrices. We present a randomized polynomial-time algorithm that solves this problem with an arbitrarily high success probability and outputs transforming matrices U and V.

10amatrix polynomials10aSchwartz-Zippel lemma10aunitary transformations1 aChitambar, Eric1 aMiller, Carl1 aShi, Yaoyun uhttp://dl.acm.org/citation.cfm?id=2230936.223094201241nas a2200181 4500008004100000245007500041210006900116260001500185490000700200520070200207100001300909700001500922700001900937700002000956700002300976700002300999856003701022 2011 eng d00aDetecting paired and counterflow superfluidity via dipole oscillations0 aDetecting paired and counterflow superfluidity via dipole oscill c2011/10/270 v843 a We suggest an experimentally feasible procedure to observe paired and counterflow superfluidity in ultra-cold atom systems. We study the time evolution of one-dimensional mixtures of bosonic atoms in an optical lattice following an abrupt displacement of an additional weak confining potential. We find that the dynamic responses of the paired superfluid phase for attractive inter-species interactions and the counterflow superfluid phase for repulsive interactions are qualitatively distinct and reflect the quasi long-range order that characterizes these states. These findings suggest a clear experimental procedure to detect these phases, and give an intuitive insight into their dynamics. 1 aHu, Anzi1 aMathey, L.1 aTiesinga, Eite1 aDanshita, Ippei1 aWilliams, Carl, J.1 aClark, Charles, W. uhttp://arxiv.org/abs/1103.3513v301130nas a2200121 4500008004100000245010300041210006900144260001300213490000700226520071100233100002700944856003700971 2011 eng d00aA diagrammatic expansion of the Casimir energy in multiple reflections: theory and applications 0 adiagrammatic expansion of the Casimir energy in multiple reflect c2011/2/20 v833 a We develop a diagrammatic representation of the Casimir energy of a multibody configuration. The diagrams represent multiple reflections between the objects and can be organized by a few simple rules. The lowest-order diagrams (or reflections) give the main contribution to the Casimir interaction which proves the usefulness of this expansion. Among some applications of this, we find analytical formulae describing the interaction between "edges", i.e. semi-infinite plates, where we also give a first example of blocking in the context of the Casimir energy. We also find the interaction of edges with a needle and describe analytically a recent model of the repulsion due to the Casimir interaction. 1 aMaghrebi, Mohammad, F. uhttp://arxiv.org/abs/1012.1060v100981nas a2200133 4500008004100000245005900041210005900100260001300159490000800172520059000180100002400770700001600794856003700810 2011 eng d00aDirect Fidelity Estimation from Few Pauli Measurements0 aDirect Fidelity Estimation from Few Pauli Measurements c2011/6/80 v1063 a We describe a simple method for certifying that an experimental device prepares a desired quantum state rho. Our method is applicable to any pure state rho, and it provides an estimate of the fidelity between rho and the actual (arbitrary) state in the lab, up to a constant additive error. The method requires measuring only a constant number of Pauli expectation values, selected at random according to an importance-weighting rule. Our method is faster than full tomography by a factor of d, the dimension of the state space, and extends easily and naturally to quantum channels. 1 aFlammia, Steven, T.1 aLiu, Yi-Kai uhttp://arxiv.org/abs/1104.4695v301352nas a2200145 4500008004100000245007400041210006900115260001500184490000700199520089800206100002001104700002001124700002501144856003701169 2011 eng d00ad-Wave Superfluidity in Optical Lattices of Ultracold Polar Molecules0 adWave Superfluidity in Optical Lattices of Ultracold Polar Molec c2011/12/290 v843 a Recent work on ultracold polar molecules, governed by a generalization of the t-J Hamiltonian, suggests that molecules may be better suited than atoms for studying d-wave superfluidity due to stronger interactions and larger tunability of the system. We compute the phase diagram for polar molecules in a checkerboard lattice consisting of weakly coupled square plaquettes. In the simplest experimentally realizable case where there is only tunneling and an XX-type spin-spin interaction, we identify the parameter regime where d-wave superfluidity occurs. We also find that the inclusion of a density-density interaction destroys the superfluid phase and that the inclusion of a spin-density or an Ising-type spin-spin interaction can enhance the superfluid phase. We also propose schemes for experimentally realizing the perturbative calculations exhibiting enhanced d-wave superfluidity. 1 aKuns, Kevin, A.1 aRey, Ana, Maria1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1110.5330v201276nas a2200157 4500008004100000245008200041210006900123260001500192300001100207490000700218520080100225100001901026700001801045700001801063856003701081 2011 eng d00aDynamics of Overhauser Field under nuclear spin diffusion in a quantum dot 0 aDynamics of Overhauser Field under nuclear spin diffusion in a q c2011/03/25 a0330360 v133 a The coherence of electron spin can be significantly enhanced by locking the Overhauser field from nuclear spins using the nuclear spin preparation. We propose a theoretical model to calculate the long time dynamics of the Overhauser field under intrinsic nuclear spin diffusion in a quantum dot. We obtain a simplified diffusion equation that can be numerically solved and show quantitatively how the Knight shift and the electron-mediated nuclear spin flip-flop affect the nuclear spin diffusion. The results explain several recent experimental observations, where the decay time of Overhauser field is measured under different configurations, including variation of the external magnetic field, the electron spin configuration in a double dot, and the initial nuclear spin polarization rate. 1 aGong, Zhe-Xuan1 aYin, Zhang-qi1 aDuan, L., -M. uhttp://arxiv.org/abs/0912.4322v100869nas a2200133 4500008004100000245005100041210004200092260001500134520048400149100002400633700002000657700002100677856003700698 2010 eng d00aOn the degeneracy of SU(3)k topological phases0 adegeneracy of SU3k topological phases c2010/09/013 a

The ground state degeneracy of an $SU(N)_k$ topological phase with $n$ quasiparticle excitations is relevant quantity for quantum computation, condensed matter physics, and knot theory. It is an open question to find a closed formula for this degeneracy for any $N > 2$. Here we present the problem in an explicit combinatorial way and analyze the case N=3. While not finding a complete closed-form solution, we obtain generating functions and solve some special cases.

1 aJordan, Stephen, P.1 aMansour, Toufik1 aSeverini, Simone uhttp://arxiv.org/abs/1009.0114v101401nas a2200217 4500008004100000245005600041210005600097260001300153490000800166520081300174100002100987700001801008700001901026700001401045700002101059700001901080700001401099700001501113700001801128856003701146 2010 eng d00aDynamic Nuclear Polarization in Double Quantum Dots0 aDynamic Nuclear Polarization in Double Quantum Dots c2010/6/40 v1043 aWe theoretically investigate the controlled dynamic polarization of lattice nuclear spins in GaAs double quantum dots containing two electrons. Three regimes of long-term dynamics are identified, including the build up of a large difference in the Overhauser fields across the dots, the saturation of the nuclear polarization process associated with formation of so-called "dark states," and the elimination of the difference field. We show that in the case of unequal dots, build up of difference fields generally accompanies the nuclear polarization process, whereas for nearly identical dots, build up of difference fields competes with polarization saturation in dark states. The elimination of the difference field does not, in general, correspond to a stable steady state of the polarization process. 1 aGullans, Michael1 aKrich, J., J.1 aTaylor, J., M.1 aBluhm, H.1 aHalperin, B., I.1 aMarcus, C., M.1 aStopa, M.1 aYacoby, A.1 aLukin, M., D. uhttp://arxiv.org/abs/1003.4508v200832nas a2200169 4500008004100000245005200041210005100093260001500144300001400159490000600173520035600179100002300535700001900558700002400577700001700601856004400618 2009 eng d00aDiscrete-query quantum algorithm for NAND trees0 aDiscretequery quantum algorithm for NAND trees c2009/07/01 a119 - 1230 v53 a Recently, Farhi, Goldstone, and Gutmann gave a quantum algorithm for evaluating NAND trees that runs in time O(sqrt(N log N)) in the Hamiltonian query model. In this note, we point out that their algorithm can be converted into an algorithm using O(N^{1/2 + epsilon}) queries in the conventional quantum query model, for any fixed epsilon > 0. 1 aChilds, Andrew, M.1 aCleve, Richard1 aJordan, Stephen, P.1 aYeung, David uhttp://arxiv.org/abs/quant-ph/0702160v100765nas a2200145 4500008004100000245005100041210005000092260001400142300001100156490000700167520036000174100001900534700002300553856004300576 2005 eng d00aDecoherence in Quantum Walks on the Hypercube 0 aDecoherence in Quantum Walks on the Hypercube c12/5/2005 a0623040 v763 a

We study a natural notion of decoherence on quantum random walks over the hypercube. We prove that in this model there is a decoherence threshold beneath which the essential properties of the hypercubic quantum walk, such as linear mixing times, are preserved. Beyond the threshold, we prove that the walks behave like their classical counterparts.

1 aAlagic, Gorjan1 aRussell, Alexander uhttps://arxiv.org/abs/quant-ph/050116901484nas a2200121 4500008004100000245007100041210006900112260001500181520108500196100001901281700001801300856004401318 2005 eng d00aDephasing of quantum bits by a quasi-static mesoscopic environment0 aDephasing of quantum bits by a quasistatic mesoscopic environmen c2005/12/073 aWe examine coherent processes in a two-state quantum system that is strongly coupled to a mesoscopic spin bath and weakly coupled to other environmental degrees of freedom. Our analysis is specifically aimed at understanding the quantum dynamics of solid-state quantum bits such as electron spins in semiconductor structures and superconducting islands. The role of mesoscopic degrees of freedom with long correlation times (local degrees of freedom such as nuclear spins and charge traps) in qubit-related dephasing is discussed in terms of a quasi-static bath. A mathemat- ical framework simultaneously describing coupling to the slow mesoscopic bath and a Markovian environment is developed and the dephasing and decoherence properties of the total system are investigated. The model is applied to several specific examples with direct relevance to current ex- periments. Comparisons to experiments suggests that such quasi-static degrees of freedom play an important role in current qubit implementations. Several methods of mitigating the bath-induced error are considered. 1 aTaylor, J., M.1 aLukin, M., D. uhttp://arxiv.org/abs/quant-ph/0512059v201235nas a2200145 4500008004100000245005000041210004800091260001500139300001200154520081600166100001900982700001601001700001601017856005601033 2005 eng d00aDesigning Incentives for Peer-to-Peer Routing0 aDesigning Incentives for PeertoPeer Routing c2005/03/13 a374-3853 aIn a peer-to-peer network, nodes are typically required to route packets for each other. This leads to a problem of “free-loaders,” nodes that use the network but refuse to route other nodes’ packets. In this paper we study ways of designing incentives to discourage free-loading. We model the interactions between nodes as a “random matching game,” and describe a simple reputation system that provides incentives for good behavior. Under certain assumptions, we obtain a stable subgame-perfect equilibrium. We use simulations to investigate the robustness of this scheme in the presence of noise and malicious nodes, and we examine some of the design trade-offs. We also evaluate some possible adversarial strategies, and discuss how our results might apply to real peer-to-peer systems.1 aBlanc, Alberto1 aLiu, Yi-Kai1 aVahda, Amin uhttp://cseweb.ucsd.edu/~vahdat/papers/infocom05.pdf