TY - JOUR T1 - Quantum computational advantage via high-dimensional Gaussian boson sampling JF - Science Advances Y1 - 2022 A1 - Abhinav Deshpande A1 - Arthur Mehta A1 - Trevor Vincent A1 - Nicolas Quesada A1 - Marcel Hinsche A1 - Marios Ioannou A1 - Lars Madsen A1 - Jonathan Lavoie A1 - Haoyu Qi A1 - Jens Eisert A1 - Dominik Hangleiter A1 - Bill Fefferman A1 - Ish Dhand AB -

A programmable quantum computer based on fiber optics outperforms classical computers with a high level of confidence. Photonics is a promising platform for demonstrating a quantum computational advantage (QCA) by outperforming the most powerful classical supercomputers on a well-defined computational task. Despite this promise, existing proposals and demonstrations face challenges. Experimentally, current implementations of Gaussian boson sampling (GBS) lack programmability or have prohibitive loss rates. Theoretically, there is a comparative lack of rigorous evidence for the classical hardness of GBS. In this work, we make progress in improving both the theoretical evidence and experimental prospects. We provide evidence for the hardness of GBS, comparable to the strongest theoretical proposals for QCA. We also propose a QCA architecture we call high-dimensional GBS, which is programmable and can be implemented with low loss using few optical components. We show that particular algorithms for simulating GBS are outperformed by high-dimensional GBS experiments at modest system sizes. This work thus opens the path to demonstrating QCA with programmable photonic processors.

VL - 8 U4 - eabi7894 UR - https://www.science.org/doi/abs/10.1126/sciadv.abi7894 U5 - 10.1126/sciadv.abi7894 ER - TY - JOUR T1 - A single T-gate makes distribution learning hard Y1 - 2022 A1 - Marcel Hinsche A1 - Marios Ioannou A1 - Alexander Nietner A1 - Jonas Haferkamp A1 - Yihui Quek A1 - Dominik Hangleiter A1 - Jean-Pierre Seifert A1 - Jens Eisert A1 - Ryan Sweke AB -

The task of learning a probability distribution from samples is ubiquitous across the natural sciences. The output distributions of local quantum circuits form a particularly interesting class of distributions, of key importance both to quantum advantage proposals and a variety of quantum machine learning algorithms. In this work, we provide an extensive characterization of the learnability of the output distributions of local quantum circuits. Our first result yields insight into the relationship between the efficient learnability and the efficient simulatability of these distributions. Specifically, we prove that the density modelling problem associated with Clifford circuits can be efficiently solved, while for depth d=nΩ(1) circuits the injection of a single T-gate into the circuit renders this problem hard. This result shows that efficient simulatability does not imply efficient learnability. Our second set of results provides insight into the potential and limitations of quantum generative modelling algorithms. We first show that the generative modelling problem associated with depth d=nΩ(1) local quantum circuits is hard for any learning algorithm, classical or quantum. As a consequence, one cannot use a quantum algorithm to gain a practical advantage for this task. We then show that, for a wide variety of the most practically relevant learning algorithms -- including hybrid-quantum classical algorithms -- even the generative modelling problem associated with depth d=ω(log(n)) Clifford circuits is hard. This result places limitations on the applicability of near-term hybrid quantum-classical generative modelling algorithms.

UR - https://arxiv.org/abs/2207.03140 ER - TY - JOUR T1 - Snowmass 2021 White Paper: The Windchime Project Y1 - 2022 A1 - The Windchime Collaboration A1 - Attanasio, Alaina A1 - Bhave, Sunil A. A1 - Blanco, Carlos A1 - Carney, Daniel A1 - Demarteau, Marcel A1 - Elshimy, Bahaa A1 - Febbraro, Michael A1 - Feldman, Matthew A. A1 - Ghosh, Sohitri A1 - Hickin, Abby A1 - Hong, Seongjin A1 - Lang, Rafael F. A1 - Lawrie, Benjamin A1 - Li, Shengchao A1 - Liu, Zhen A1 - Maldonado, Juan P. A. A1 - Marvinney, Claire A1 - Oo, Hein Zay Yar A1 - Pai, Yun-Yi A1 - Pooser, Raphael A1 - Qin, Juehang A1 - Sparmann, Tobias J. A1 - Taylor, Jacob M. A1 - Tian, Hao A1 - Tunnell, Christopher KW - Cosmology and Nongalactic Astrophysics (astro-ph.CO) KW - FOS: Physical sciences KW - High Energy Physics - Experiment (hep-ex) KW - High Energy Physics - Phenomenology (hep-ph) AB -

The absence of clear signals from particle dark matter in direct detection experiments motivates new approaches in disparate regions of viable parameter space. In this Snowmass white paper, we outline the Windchime project, a program to build a large array of quantum-enhanced mechanical sensors. The ultimate aim is to build a detector capable of searching for Planck mass-scale dark matter purely through its gravitational coupling to ordinary matter. In the shorter term, we aim to search for a number of other physics targets, especially some ultralight dark matter candidates. Here, we discuss the basic design, open R&D challenges and opportunities, current experimental efforts, and both short- and long-term physics targets of the Windchime project.

UR - https://arxiv.org/abs/2203.07242 U5 - 10.48550/ARXIV.2203.07242 ER - TY - JOUR T1 - Learnability of the output distributions of local quantum circuits Y1 - 2021 A1 - Marcel Hinsche A1 - Marios Ioannou A1 - Alexander Nietner A1 - Jonas Haferkamp A1 - Yihui Quek A1 - Dominik Hangleiter A1 - Jean-Pierre Seifert A1 - Jens Eisert A1 - Ryan Sweke AB -

There is currently a large interest in understanding the potential advantages quantum devices can offer for probabilistic modelling. In this work we investigate, within two different oracle models, the probably approximately correct (PAC) learnability of quantum circuit Born machines, i.e., the output distributions of local quantum circuits. We first show a negative result, namely, that the output distributions of super-logarithmic depth Clifford circuits are not sample-efficiently learnable in the statistical query model, i.e., when given query access to empirical expectation values of bounded functions over the sample space. This immediately implies the hardness, for both quantum and classical algorithms, of learning from statistical queries the output distributions of local quantum circuits using any gate set which includes the Clifford group. As many practical generative modelling algorithms use statistical queries -- including those for training quantum circuit Born machines -- our result is broadly applicable and strongly limits the possibility of a meaningful quantum advantage for learning the output distributions of local quantum circuits. As a positive result, we show that in a more powerful oracle model, namely when directly given access to samples, the output distributions of local Clifford circuits are computationally efficiently PAC learnable by a classical learner. Our results are equally applicable to the problems of learning an algorithm for generating samples from the target distribution (generative modelling) and learning an algorithm for evaluating its probabilities (density modelling). They provide the first rigorous insights into the learnability of output distributions of local quantum circuits from the probabilistic modelling perspective. 

UR - https://arxiv.org/abs/2110.05517 ER - TY - JOUR T1 - Quantum Computational Supremacy via High-Dimensional Gaussian Boson Sampling Y1 - 2021 A1 - Abhinav Deshpande A1 - Arthur Mehta A1 - Trevor Vincent A1 - Nicolas Quesada A1 - Marcel Hinsche A1 - Marios Ioannou A1 - Lars Madsen A1 - Jonathan Lavoie A1 - Haoyu Qi A1 - Jens Eisert A1 - Dominik Hangleiter A1 - Bill Fefferman A1 - Ish Dhand AB -

Photonics is a promising platform for demonstrating quantum computational supremacy (QCS) by convincingly outperforming the most powerful classical supercomputers on a well-defined computational task. Despite this promise, existing photonics proposals and demonstrations face significant hurdles. Experimentally, current implementations of Gaussian boson sampling lack programmability or have prohibitive loss rates. Theoretically, there is a comparative lack of rigorous evidence for the classical hardness of GBS. In this work, we make significant progress in improving both the theoretical evidence and experimental prospects. On the theory side, we provide strong evidence for the hardness of Gaussian boson sampling, placing it on par with the strongest theoretical proposals for QCS. On the experimental side, we propose a new QCS architecture, high-dimensional Gaussian boson sampling, which is programmable and can be implemented with low loss rates using few optical components. We show that particular classical algorithms for simulating GBS are vastly outperformed by high-dimensional Gaussian boson sampling experiments at modest system sizes. This work thus opens the path to demonstrating QCS with programmable photonic processors.

UR - https://arxiv.org/abs/2102.12474 ER - TY - JOUR T1 - Robust Self-Testing of Multiparticle Entanglement JF - Phys. Rev. Lett. Y1 - 2021 A1 - Dian Wu A1 - Qi Zhao A1 - Xue-Mei Gu A1 - Han-Sen Zhong A1 - You Zhou A1 - Li-Chao Peng A1 - Jian Qin A1 - Yi-Han Luo A1 - Kai Chen A1 - Li Li A1 - Nai-Le Liu A1 - Chao-Yang Lu A1 - Jian-Wei Pan AB -

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.

VL - 127 U4 - 230503 UR - https://arxiv.org/abs/2105.10298 U5 - https://doi.org/10.1103/PhysRevLett.127.230503 ER - TY - JOUR T1 - Building Bulk Geometry from the Tensor Radon Transform JF - Journal of High Energy Physics Y1 - 2020 A1 - ChunJun Cao A1 - Xiao-Liang Q A1 - Brian Swingle A1 - Eugene Tang AB -

Using the tensor Radon transform and related numerical methods, we study how bulk geometries can be explicitly reconstructed from boundary entanglement entropies in the specific case of AdS3/CFT2. We find that, given the boundary entanglement entropies of a 2d CFT, this framework provides a quantitative measure that detects whether the bulk dual is geometric in the perturbative (near AdS) limit. In the case where a well-defined bulk geometry exists, we explicitly reconstruct the unique bulk metric tensor once a gauge choice is made. We then examine the emergent bulk geometries for static and dynamical scenarios in holography and in many-body systems. Apart from the physics results, our work demonstrates that numerical methods are feasible and effective in the study of bulk reconstruction in AdS/CFT.

VL - 2020 U4 - 1-50 UR - https://arxiv.org/abs/2007.00004 CP - 12 ER - TY - JOUR T1 - Confronting lattice parton distributions with global QCD analysis Y1 - 2020 A1 - Jacob Bringewatt A1 - N. Sato A1 - W. Melnitchouk A1 - Jian-Wei Qiu A1 - F. Steffens A1 - M. Constantinou AB -

We present the first Monte Carlo based global QCD analysis of spin-averaged and spin-dependent parton distribution functions (PDFs) that includes nucleon isovector matrix elements in coordinate space from lattice QCD. We investigate the degree of universality of the extracted PDFs when the lattice and experimental data are treated under the same conditions within the Bayesian likelihood analysis. For the unpolarized sector, we find rather weak constraints from the current lattice data on the phenomenological PDFs, and difficulties in describing the lattice matrix elements at large spatial distances. In contrast, for the polarized PDFs we find good agreement between experiment and lattice data, with the latter providing significant constraints on the spin-dependent isovector quark and antiquark distributions

UR - https://arxiv.org/abs/2010.00548 ER - TY - JOUR T1 - Mechanical Quantum Sensing in the Search for Dark Matter Y1 - 2020 A1 - D. Carney A1 - G. Krnjaic A1 - D. C. Moore A1 - C. A. Regal A1 - G. Afek A1 - S. Bhave A1 - B. Brubaker A1 - T. Corbitt A1 - J. Cripe A1 - N. Crisosto A1 - A.Geraci A1 - S. Ghosh A1 - J. G. E. Harris A1 - A. Hook A1 - E. W. Kolb A1 - J. Kunjummen A1 - R. F. Lang A1 - T. Li A1 - T. Lin A1 - Z. Liu A1 - J. Lykken A1 - L. Magrini A1 - J. Manley A1 - N. Matsumoto A1 - A. Monte A1 - F. Monteiro A1 - T. Purdy A1 - C. J. Riedel A1 - R. Singh A1 - S. Singh A1 - K. Sinha A1 - J. M. Taylor A1 - J. Qin A1 - D. J. Wilson A1 - Y. Zhao AB -

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

UR - https://arxiv.org/abs/2008.06074 ER - TY - JOUR T1 - Optimal control for quantum detectors Y1 - 2020 A1 - Paraj Titum A1 - Kevin M. Schultz A1 - Alireza Seif A1 - Gregory D. Quiroz A1 - B. D. Clader AB -

Quantum systems are promising candidates for sensing of weak signals as they can provide unrivaled performance when estimating parameters of external fields. However, when trying to detect weak signals that are hidden by background noise, the signal-to-noise-ratio is a more relevant metric than raw sensitivity. We identify, under modest assumptions about the statistical properties of the signal and noise, the optimal quantum control to detect an external signal in the presence of background noise using a quantum sensor. Interestingly, for white background noise, the optimal solution is the simple and well-known spin-locking control scheme. We further generalize, using numerical techniques, these results to the background noise being a correlated Lorentzian spectrum. We show that for increasing correlation time, pulse based sequences such as CPMG are also close to the optimal control for detecting the signal, with the crossover dependent on the signal frequency. These results show that an optimal detection scheme can be easily implemented in near-term quantum sensors without the need for complicated pulse shaping.

UR - https://arxiv.org/abs/2005.05995 ER - TY - JOUR T1 - Optimal Measurement of Field Properties with Quantum Sensor Networks Y1 - 2020 A1 - Timothy Qian A1 - Jacob Bringewatt A1 - Igor Boettcher A1 - Przemyslaw Bienias A1 - Alexey V. Gorshkov AB -

We consider a quantum sensor network of qubit sensors coupled to a field f(x⃗ ;θ⃗ ) analytically parameterized by the vector of parameters θ⃗ . The qubit sensors are fixed at positions x⃗ 1,…,x⃗ d. While the functional form of f(x⃗ ;θ⃗ ) is known, the parameters θ⃗  are not. We derive saturable bounds on the precision of measuring an arbitrary analytic function q(θ⃗ ) of these parameters and construct the optimal protocols that achieve these bounds. Our results are obtained from a combination of techniques from quantum information theory and duality theorems for linear programming. They can be applied to many problems, including optimal placement of quantum sensors, field interpolation, and the measurement of functionals of parametrized fields.

UR - https://arxiv.org/abs/2011.01259 ER - TY - JOUR T1 - Heisenberg-Scaling Measurement Protocol for Analytic Functions with Quantum Sensor Networks JF - Phys. Rev. A Y1 - 2019 A1 - Kevin Qian A1 - Zachary Eldredge A1 - Wenchao Ge A1 - Guido Pagano A1 - Christopher Monroe A1 - James V. Porto A1 - Alexey V. Gorshkov AB -

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

VL - 100 UR - https://arxiv.org/abs/1901.09042 CP - 042304 U5 - https://doi.org/10.1103/PhysRevA.100.042304 ER - TY - JOUR T1 - Energy-level statistics in strongly disordered systems with power-law hopping JF - Phys. Rev. Y1 - 2018 A1 - Paraj Titum A1 - Victor L. Quito A1 - Sergey V. Syzranov AB -

Motivated by neutral excitations in disordered electronic materials and systems of trapped ultracold particles with long-range interactions, we study energy-level statistics of quasiparticles with the power-law hopping Hamiltonian ∝1/rα in a strong random potential. In solid-state systems such quasiparticles, which are exemplified by neutral dipolar excitations, lead to long-range correlations of local observables and may dominate energy transport. Focussing on the excitations in disordered electronic systems, we compute the energy-level correlation function R2(ω) in a finite system in the limit of sufficiently strong disorder. At small energy differences the correlations exhibit Wigner-Dyson statistics. In particular, in the limit of very strong disorder the energy-level correlation function is given by R2(ω,V)=A3ωωV for small frequencies ω≪ωV and R2(ω,V)=1−(α−d)A1(ωVω)dα−A2(ωVω)2 for large frequencies ω≫ωV, where ωV∝V−αd is the characteristic matrix element of excitation hopping in a system of volume V, and A1, A2 and A3 are coefficient of order unity which depend on the shape of the system. The energy-level correlation function, which we study, allows for a direct experimental observation, for example, by measuring the correlations of the ac conductance of the system at different frequencies.

VL - B U4 - 014201 UR - https://arxiv.org/abs/1803.11178 CP - 98 U5 - https://doi.org/10.1103/PhysRevB.98.014201 ER - TY - JOUR T1 - Reply to Comment on "Space-Time Crystals of Trapped Ions Y1 - 2012 A1 - Tongcang Li A1 - Zhe-Xuan Gong A1 - Zhang-qi Yin A1 - H. T. Quan A1 - Xiaobo Yin A1 - Peng Zhang A1 - L. -M. Duan A1 - Xiang Zhang AB - This is a reply to the comment from Patrick Bruno (arXiv:1211.4792) on our paper (Phys. Rev. Lett. 109, 163001 (2012)). UR - http://arxiv.org/abs/1212.6959v2 U5 - http://dx.doi.org/10.1103/PhysRevLett.109.163001 ER - TY - JOUR T1 - Space-Time Crystals of Trapped Ions JF - Physical Review Letters Y1 - 2012 A1 - Tongcang Li A1 - Gong, Zhe-Xuan A1 - Yin, Zhang-Qi A1 - Quan, H. T. A1 - Yin, Xiaobo A1 - Zhang, Peng A1 - Duan, L.-M. A1 - Zhang, Xiang AB - Spontaneous symmetry breaking can lead to the formation of time crystals, as well as spatial crystals. Here we propose a space-time crystal of trapped ions and a method to realize it experimentally by confining ions in a ring-shaped trapping potential with a static magnetic field. The ions spontaneously form a spatial ring crystal due to Coulomb repulsion. This ion crystal can rotate persistently at the lowest quantum energy state in magnetic fields with fractional fluxes. The persistent rotation of trapped ions produces the temporal order, leading to the formation of a space-time crystal. We show that these space-time crystals are robust for direct experimental observation. We also study the effects of finite temperatures on the persistent rotation. The proposed space-time crystals of trapped ions provide a new dimension for exploring many-body physics and emerging properties of matter. VL - 109 U4 - 163001 UR - http://link.aps.org/doi/10.1103/PhysRevLett.109.163001 CP - 16 U5 - 10.1103/PhysRevLett.109.163001 ER -