%0 Journal Article %J Science Advances %D 2022 %T Quantum computational advantage via high-dimensional Gaussian boson sampling %A Abhinav Deshpande %A Arthur Mehta %A Trevor Vincent %A Nicolas Quesada %A Marcel Hinsche %A Marios Ioannou %A Lars Madsen %A Jonathan Lavoie %A Haoyu Qi %A Jens Eisert %A Dominik Hangleiter %A Bill Fefferman %A Ish Dhand %X

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.

%B Science Advances %V 8 %P eabi7894 %8 1/5/2022 %G eng %U https://www.science.org/doi/abs/10.1126/sciadv.abi7894 %R 10.1126/sciadv.abi7894 %0 Journal Article %D 2022 %T A single T-gate makes distribution learning hard %A Marcel Hinsche %A Marios Ioannou %A Alexander Nietner %A Jonas Haferkamp %A Yihui Quek %A Dominik Hangleiter %A Jean-Pierre Seifert %A Jens Eisert %A Ryan Sweke %X

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.

%8 7/7/2022 %G eng %U https://arxiv.org/abs/2207.03140 %0 Journal Article %D 2022 %T Snowmass 2021 White Paper: The Windchime Project %A The Windchime Collaboration %A Attanasio, Alaina %A Bhave, Sunil A. %A Blanco, Carlos %A Carney, Daniel %A Demarteau, Marcel %A Elshimy, Bahaa %A Febbraro, Michael %A Feldman, Matthew A. %A Ghosh, Sohitri %A Hickin, Abby %A Hong, Seongjin %A Lang, Rafael F. %A Lawrie, Benjamin %A Li, Shengchao %A Liu, Zhen %A Maldonado, Juan P. A. %A Marvinney, Claire %A Oo, Hein Zay Yar %A Pai, Yun-Yi %A Pooser, Raphael %A Qin, Juehang %A Sparmann, Tobias J. %A Taylor, Jacob M. %A Tian, Hao %A Tunnell, Christopher %K Cosmology and Nongalactic Astrophysics (astro-ph.CO) %K FOS: Physical sciences %K High Energy Physics - Experiment (hep-ex) %K High Energy Physics - Phenomenology (hep-ph) %X

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.

%8 3/14/2022 %G eng %U https://arxiv.org/abs/2203.07242 %R 10.48550/ARXIV.2203.07242 %0 Journal Article %D 2021 %T Learnability of the output distributions of local quantum circuits %A Marcel Hinsche %A Marios Ioannou %A Alexander Nietner %A Jonas Haferkamp %A Yihui Quek %A Dominik Hangleiter %A Jean-Pierre Seifert %A Jens Eisert %A Ryan Sweke %X

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. 

%8 10/11/2021 %G eng %U https://arxiv.org/abs/2110.05517 %0 Journal Article %D 2021 %T Quantum Computational Supremacy via High-Dimensional Gaussian Boson Sampling %A Abhinav Deshpande %A Arthur Mehta %A Trevor Vincent %A Nicolas Quesada %A Marcel Hinsche %A Marios Ioannou %A Lars Madsen %A Jonathan Lavoie %A Haoyu Qi %A Jens Eisert %A Dominik Hangleiter %A Bill Fefferman %A Ish Dhand %X

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.

%8 2/24/2021 %G eng %U https://arxiv.org/abs/2102.12474 %0 Journal Article %J Phys. Rev. Lett. %D 2021 %T Robust Self-Testing of Multiparticle Entanglement %A Dian Wu %A Qi Zhao %A Xue-Mei Gu %A Han-Sen Zhong %A You Zhou %A Li-Chao Peng %A Jian Qin %A Yi-Han Luo %A Kai Chen %A Li Li %A Nai-Le Liu %A Chao-Yang Lu %A Jian-Wei Pan %X

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.

%B Phys. Rev. Lett. %V 127 %P 230503 %8 12/7/2021 %G eng %U https://arxiv.org/abs/2105.10298 %R https://doi.org/10.1103/PhysRevLett.127.230503 %0 Journal Article %J Journal of High Energy Physics %D 2020 %T Building Bulk Geometry from the Tensor Radon Transform %A ChunJun Cao %A Xiao-Liang Q %A Brian Swingle %A Eugene Tang %X

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.

%B Journal of High Energy Physics %V 2020 %P 1-50 %8 12/4/2020 %G eng %U https://arxiv.org/abs/2007.00004 %N 12 %0 Journal Article %D 2020 %T Confronting lattice parton distributions with global QCD analysis %A Jacob Bringewatt %A N. Sato %A W. Melnitchouk %A Jian-Wei Qiu %A F. Steffens %A M. Constantinou %X

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

%8 10/1/2020 %G eng %U https://arxiv.org/abs/2010.00548 %0 Journal Article %D 2020 %T Mechanical Quantum Sensing in the Search for Dark Matter %A D. Carney %A G. Krnjaic %A D. C. Moore %A C. A. Regal %A G. Afek %A S. Bhave %A B. Brubaker %A T. Corbitt %A J. Cripe %A N. Crisosto %A A.Geraci %A S. Ghosh %A J. G. E. Harris %A A. Hook %A E. W. Kolb %A J. Kunjummen %A R. F. Lang %A T. Li %A T. Lin %A Z. Liu %A J. Lykken %A L. Magrini %A J. Manley %A N. Matsumoto %A A. Monte %A F. Monteiro %A T. Purdy %A C. J. Riedel %A R. Singh %A S. Singh %A K. Sinha %A J. M. Taylor %A J. Qin %A D. J. Wilson %A Y. Zhao %X

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.

%8 8/13/2020 %G eng %U https://arxiv.org/abs/2008.06074 %9 FERMILAB-PUB-20-378-QIS-T %0 Journal Article %D 2020 %T Optimal control for quantum detectors %A Paraj Titum %A Kevin M. Schultz %A Alireza Seif %A Gregory D. Quiroz %A B. D. Clader %X

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.

%8 5/12/2020 %G eng %U https://arxiv.org/abs/2005.05995 %0 Journal Article %D 2020 %T Optimal Measurement of Field Properties with Quantum Sensor Networks %A Timothy Qian %A Jacob Bringewatt %A Igor Boettcher %A Przemyslaw Bienias %A Alexey V. Gorshkov %X

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.

%8 11/2/2020 %G eng %U https://arxiv.org/abs/2011.01259 %0 Journal Article %J Phys. Rev. A %D 2019 %T Heisenberg-Scaling Measurement Protocol for Analytic Functions with Quantum Sensor Networks %A Kevin Qian %A Zachary Eldredge %A Wenchao Ge %A Guido Pagano %A Christopher Monroe %A James V. Porto %A Alexey V. Gorshkov %X

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.

%B Phys. Rev. A %V 100 %8 10/7/2019 %G eng %U https://arxiv.org/abs/1901.09042 %N 042304 %R https://doi.org/10.1103/PhysRevA.100.042304 %0 Journal Article %J Phys. Rev. %D 2018 %T Energy-level statistics in strongly disordered systems with power-law hopping %A Paraj Titum %A Victor L. Quito %A Sergey V. Syzranov %X

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.

%B Phys. Rev. %V B %P 014201 %8 2018/07/16 %G eng %U https://arxiv.org/abs/1803.11178 %N 98 %R https://doi.org/10.1103/PhysRevB.98.014201 %0 Journal Article %D 2012 %T Reply to Comment on "Space-Time Crystals of Trapped Ions %A Tongcang Li %A Zhe-Xuan Gong %A Zhang-qi Yin %A H. T. Quan %A Xiaobo Yin %A Peng Zhang %A L. -M. Duan %A Xiang Zhang %X This is a reply to the comment from Patrick Bruno (arXiv:1211.4792) on our paper (Phys. Rev. Lett. 109, 163001 (2012)). %8 2012/10/15 %G eng %U http://arxiv.org/abs/1212.6959v2 %R http://dx.doi.org/10.1103/PhysRevLett.109.163001 %0 Journal Article %J Physical Review Letters %D 2012 %T Space-Time Crystals of Trapped Ions %A Tongcang Li %A Gong, Zhe-Xuan %A Yin, Zhang-Qi %A Quan, H. T. %A Yin, Xiaobo %A Zhang, Peng %A Duan, L.-M. %A Zhang, Xiang %X 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. %B Physical Review Letters %V 109 %P 163001 %8 2012/10/19 %G eng %U http://link.aps.org/doi/10.1103/PhysRevLett.109.163001 %N 16 %R 10.1103/PhysRevLett.109.163001