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arXiv 2021年

作者： Zhao, Yuan-Yuan Rozpędek, Filip Hou, Zhibo Wu, Kang-Da Xiang, Guo-Yong Li, Chuan-Feng Guo, Guang-Can Key Laboratory of Quantum Information University of Science and Technology of China CAS Hefei230026 China Center for Quantum Computing Peng Cheng Laboratory Shenzhen518055 China CAS Center for Excellence in Quantum Information and Quantum Physics University of Science and Technology of China Hefei230026 China QuTech Delft University of Technology Lorentzweg 1 Delft2628 CJ Netherlands Kavli Institute of Nanoscience Delft University of Technology Lorentzweg 1 Delft2628 CJ Netherlands Pritzker School of Molecular Engineering University of Chicago ChicagoIL60637 United States

quantum uncertainty is a well-known property of quantum mechanics that states the impossibility of predicting measurement outcomes of multiple incompatible observables simultaneously. In contrast, the uncertainty in the classical domain comes from the lack of information about the exact state of the system. One may naturally ask, whether the quantum uncertainty is indeed a fully intrinsic property of the quantum theory, or whether similar to the classical domain lack of knowledge about specific parts of the physical system might be the source of this uncertainty. This question has been addressed in the previous literature where the authors argue that in the entropic formulation of the uncertainty principle that can be illustrated using the so-called, guessing games, indeed such lack of information has a significant contribution to the arising quantum uncertainty. Here we investigate this issue experimentally by implementing the corresponding two-dimensional and three-dimensional guessing games. Our results confirm that within the guessing-game framework, the quantum uncertainty to a large extent relies on the fact that quantum information determining the key properties of the game is stored in the degrees of freedom that remain inaccessible to the guessing party. Moreover, we offer an experimentally compact method to construct the high-dimensional Fourier gate which is a major building block for various tasks in quantum computation, quantum communication, and quantum metrology. Copyright © 2021, The Authors. All rights reserved.

关键词： quantum communication

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Dynamical process of a bit-width reduced Ising model with simulated annealing

arXiv

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arXiv 2023年

作者： Kikuchi, Shuta Togawa, Nozomu Tanaka, Shu Department of Applied Physics and Physico-Informatics Keio University Kanagawa223-8522 Japan Department of Computer Science and Communications Engineering Waseda University Tokyo169-8555 Japan Human Biology-Microbiome-Quantum Research Center WPI-Bio2Q Keio University Tokyo108-8345 Japan Green Computing System Research Organization Waseda University Tokyo162-0042 Japan International Research Frontiers Initiative Tokyo Institute of Technology Tokyo108-0023 Japan

Ising machines have attracted attention as efficient solvers for combinatorial optimization problems, which are formulated as ground-state (lowest-energy) search problems of the Ising model. Due to the limited bit-width of coefficients on Ising machines, the Ising model must be transformed into a bit-width reduced (BWR) Ising model. According to previous research, the bit-width reduction method, which adds auxiliary spins, ensures that the ground state of the BWR Ising model is theoretically the same as the Ising model before bit-width reduction (original Ising model). However, while the dynamical process is closely related to solution accuracy, how the BWR Ising model progresses towards the ground state remains to be elucidated. Therefore, we compared the dynamical processes of these models using simulated annealing (SA). Our findings reveal significant differences in the dynamical process across models. Analysis from the viewpoint of statistical mechanics found that the BWR Ising model has two characteristic properties: an effective temperature and a slow relaxation. These properties alter the temperature schedule and spin flip probability in the BWR Ising model, leading to differences in the dynamical process. Therefore, to obtain the same dynamical process as the original Ising model, we proposed SA parameters for the BWR Ising model. We demonstrated the proposed SA parameters using a square lattice Ising model, in which all coefficients were set uniformly to the same positive values or randomly. Our experimental evaluations demonstrated that the dynamical process of the BWR and original Ising model became closer. © 2023, CC BY.

关键词： Simulated annealing

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Logical quantum processor based on reconfigurable atom arrays

arXiv

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arXiv 2023年

作者： Bluvstein, Dolev Evered, Simon J. Geim, Alexandra A. Li, Sophie H. Zhou, Hengyun Manovitz, Tom Ebadi, Sepehr Cain, Madelyn Kalinowski, Marcin Hangleiter, Dominik Ataides, J. Pablo Bonilla Maskara, Nishad Cong, Iris Gao, Xun Rodriguez, Pedro Sales Karolyshyn, Thomas Semeghini, Giulia Gullans, Michael J. Greiner, Markus Vuletić, Vladan Lukin, Mikhail D. Department of Physics Harvard University CambridgeMA02138 United States QuEra Computing Inc. BostonMA02135 United States Joint Center for Quantum Information and Computer Science NIST University of Maryland College ParkMD20742 United States John A. Paulson School of Engineering and Applied Sciences Harvard University CambridgeMA02138 United States Department of Physics Research Laboratory of Electronics Massachusetts Institute of Technology CambridgeMA02139 United States

Suppressing errors is the central challenge for useful quantum computing [1], requiring quantum error correction [2-6] for large-scale processing. However, the overhead in the realization of error-corrected "logical" qubits, where information is encoded across many physical qubits for redundancy [2-4], poses significant challenges to large-scale logical quantum computing. Here we report the realization of a programmable quantum processor based on encoded logical qubits operating with up to 280 physical qubits. Utilizing logical-level control and a zoned architecture in reconfigurable neutral atom arrays [7], our system combines high two-qubit gate fidelities [8], arbitrary connectivity [7, 9], as well as fully programmable single-qubit rotations and mid-circuit readout [10-15]. Operating this logical processor with various types of encodings, we demonstrate improvement of a two-qubit logic gate by scaling surface code [6] distance from d = 3 to d = 7, preparation of color code qubits with break-even fidelities [5], fault-tolerant creation of logical GHZ states and feedforward entanglement teleportation, as well as operation of 40 color code qubits. Finally, using three-dimensional [[8,3,2]] code blocks [16, 17], we realize computationally complex sampling circuits [18] with up to 48 logical qubits entangled with hypercube connectivity [19] with 228 logical two-qubit gates and 48 logical CCZ gates [20]. We find that this logical encoding substantially improves algorithmic performance with error detection, outperforming physical qubit fidelities at both cross-entropy benchmarking and quantum simulations of fast scrambling [21, 22]. These results herald the advent of early error-corrected quantum computation and chart a path toward large-scale logical processors. Copyright © 2023, The Authors. All rights reserved.

关键词： Qubits

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Is there evidence for exponential quantum advantage in quantum chemistry?

arXiv

引用

arXiv 2022年

作者： Lee, Seunghoon Lee, Joonho Zhai, Huanchen Tong, Yu Dalzell, Alexander M. Kumar, Ashutosh Helms, Phillip Gray, Johnnie Cui, Zhi-Hao Liu, Wen-Yuan Kastoryano, Michael Babbush, Ryan Preskill, John Reichman, David R. Campbell, Earl T. Valeev, Edward F. Lin, Lin Chan, Garnet Kin-Lic Division of Chemistry and Chemical Engineering California Institute of Technology PasadenaCA91125 United States Department of Chemistry Columbia University New YorkNY10027 United States Department of Mathematics University of California BerkeleyCA94720 United States Aws Center for Quantum Computing PasadenaCA91125 United States Department of Chemistry Virginia Tech BlacksburgVA24061 United States Amazon Quantum Solutions Lab SeattleWA98170 United States Google Quantum AI 340 Main Street VeniceCA90291 United States Computational Research Division Lawrence Berkeley National Laboratory BerkeleyCA94720 United States Theoretical Division Los Alamos National Laboratory Los AlamosNM87545 United States Institute for Quantum Information and Matter California Institute of Technology PasadenaCA91125 United States Riverlane Cambridge United Kingdom

The idea to use quantum mechanical devices to simulate other quantum systems is commonly ascribed to Feynman. Since the original suggestion, concrete proposals have appeared for simulating molecular and materials chemistry through quantum computation, as a potential "killer application" [1, 2, 3, 4, 5]. Indications of potential exponential quantum advantage in artificial tasks [6, 7, 8, 9] have increased interest in this application, thus, it is critical to understand the basis for potential exponential quantum advantage in quantum chemistry. Here we gather the evidence for this case in the most common task in quantum chemistry, namely, ground-state energy estimation. We conclude that evidence for such an exponential advantage across chemical space has yet to be found. While quantum computers may still prove useful for quantum chemistry, it may be prudent to assume exponential speedups are not generically available for this problem. © 2022, CC BY.

关键词： quantum chemistry

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Robust second-order correlation of twin parametric beams generated by amplified spontaneous parametric down-conversion

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Chinese Optics Letters 2020年第12期18卷 63-67页

作者： Kunpeng Jia Xiaohan Wang Xinjie LV Ping Xu Zhenlin Wang ZhiWei Wuang Gang Zhao Yan-Xiao Gong Zhenda Xie Shining Zhu National Laboratory of Solid State Microstructures School of PhysicsSchool of Electronic Science and EngineeringCollege of Engineering and Applied Sciencesand Collaborative Innovation Center of Advanced MicrostructuresNanjing UniversityNanjing 210093China Institute for Quantum Information and State Key Laboratory of High Performance Computing.College of Computing National University of Defense TechnologyChangsha 410073China Mesoscopic Optics and Quantum Electronics Laboratory University of California Los AngelesCciliforniaCA 90095USA

We report an observation of the second-order correlation between twin beams generated by amplified spontaneous parametric down-conversion operating above threshold with kilowatt-level peak power, from a periodically poled Li Ta O3 crystal via a single-pass scheme. Photocurrent correlation was measured because of the bright photon streams, with raw visibility of 37.9% or 97.3% after electronic filtering. As expected in our theory, this correlation is robust and insensitive to parametric gain and detection loss, enabling important applications in optical communications, precision measurement, and nonlocal imaging.

关键词： amplified spontaneous parametric down-con version robust second-order correlation high-gain twin beams

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Perspective on“Brain Network Disorders”

Brain network disorders

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Brain network disorders 2025年第1期1卷 3-6页

作者： Zaven Khachaturian Jean-Marie C.Boutellier Jiri Damborsky Ara S.Khachaturian The Campaign to Prevent Alzheimer’s Disease 20/20(***) PotomacMD20854-3963USA The Center for Artificial Intelligence and Quantum Computing in System Brain Research(CLARA)and the International Neurodegenerative Disorders Research Center z.ú.(INDRC)EvropskaPrague16000Czech Republic Center for Neural Engineering(CNE)&Institute for Technology and Medical Systems(ITEMS) Alfred E.Mann Department of Biomedical EngineeringViterbi School of Engineering&Keck School of MedicineUniversity of Southern CaliforniaLos AngelesCA90089USA Department of Experimental Biology&RECETOX Faculty of ScienceMasaryk UniversityKamenice 5/A13Brno62500Czech Republic International Clinical Research Center St.Anne’s University Hospital BrnoPekarska 53Brno65691Czech Republic Brain Watch Coalition PotomacMD20854-3963USA

*** perspective highlights the need for a specialized publication dedicated to neuropsychiatric disorders,collectively termed“dysconnectivity syndromes.”These conditions,including dementia-Alzheimer’s disease(AD),schizophrenia,and autism spectrum disorders,result from failures in interconnected physiological systems and neural circuits rather than isolated *** proposed Brain Network Disorders(BND)journal aims to promote innovative paradigms for understanding these complex brain disorders by applying general systems theory and complexity *** aim is to broaden the traditional conceptualization of these diseases by stressing the multifactorial roots of these disorders where the focus is on the dynamic interactions among several influences and the failure of multiple overlapping nets that drive clinical manifestations。

关键词： Alzheimer s disease schizophrenia brain network disorders dysconnectivity syndromes physiological systems neural circuits brain network disorders bnd journal neuropsychiatric disorderscollectively autism spectrum disordersresult

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quantum Algorithm for Online Convex Optimization

arXiv

引用

arXiv 2020年

作者： He, Jianhao Yang, Feidiao Zhang, Jialin Li, Lvzhou Institute of Quantum Computing and Computer Science Theory School of Computer Science and Engineering Sun Yat-Sen University Guangdong Guangzhou China Institute of Computing Technology Chinese Academy of Sciences Beijing China

We explore whether quantum advantages can be found for the zeroth-order online convex optimization problem, which is also known as bandit convex optimization with multi-point feedback. In this setting, given access to zeroth-order oracles (that is, the loss function is accessed as a black box that returns the function value for any queried input), a player attempts to minimize a sequence of adversarially generated convex loss functions. This procedure can be described as a T round iterative game between the player and the adversary. In this paper, we present quantum algorithms for the problem and show for the first time that potential quantum advantages are possible for problems of online convex optimization. Specifically, our contributions are as follows. (i) When the player is allowed to query zeroth-order oracles O(1) times in each round as feedback, we give a quantum algorithm that achieves O(√T) regret without additional dependence of the dimension n, which outperforms the already known optimal classical algorithm only achieving O(√nT) regret. Note that the regret of our quantum algorithm has achieved the lower bound of classical first-order methods. (ii) We show that for strongly convex loss functions, the quantum algorithm can achieve O(log T) regret with O(1) queries as well, which means that the quantum algorithm can achieve the same regret bound as the classical algorithms in the full information setting. Copyright © 2020, The Authors. All rights reserved.

关键词： Convex optimization

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Low-depth quantum state preparation

arXiv

引用

arXiv 2021年

作者： Zhang, Xiao-Ming Yung, Man-Hong Yuan, Xiao Department of Physics City University of Hong Kong Tat Chee Avenue Kowloon Hong Kong Department of Physics Southern University of Science and Technology Shenzhen518055 China Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China Guangdong Provincial Key Laboratory of Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China Center on Frontiers of Computing Studies Department of Computer Science Peking University Beijing100871 China

A crucial subroutine in quantum computing is to load the classical data of N complex numbers into the amplitude of a superposed n = dlog2 Ne-qubit state. It has been proven that any algorithm universally implementing this subroutine would need at least O(N) constant weight operations. However, the proof assumes that only n qubits are used, whereas the circuit depth could be reduced by extending the space and allowing ancillary qubits. Here we investigate this space-time tradeoff in quantum state preparation with classical data. We propose quantum algorithms with O(n2) circuit depth to encode any N complex numbers using only single-, two-qubit gates and local measurements with ancillary qubits. Different variances of the algorithm are proposed with different space and runtime. In particular, we present a scheme with O(N2) ancillary qubits, O(n2) circuit depth, and O(n2) average runtime, which exponentially improves the conventional bound. While the algorithm requires more ancillary qubits, it consists of quantum circuit blocks that only simultaneously act on a constant number of qubits and at most O(n) qubits are entangled. We also prove a fundamental lower bound O(n) for the minimum circuit depth and runtime with arbitrary number of ancillary qubits, aligning with our scheme with O(n2). The algorithms are expected to have wide applications in both near-term and universal quantum computing. Copyright © 2021, The Authors. All rights reserved.

关键词： Qubits

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Two-dimensional ferromagnetic superlattices

引用

National Science Review 2020年第4期7卷 745-754页

作者： Shanshan Liu Ke Yang Wenqing Liu Enze Zhang Zihan Li Xiaoqian Zhang Zhiming Liao Wen Zhang Jiabao Sun Yunkun Yang Han Gao Ce Huang Linfeng Ai Ping Kwan Johnny Wong ANDrew Thye Shen Wee Alpha T.N'Diaye Simon A.Morton Xufeng Kou Jin Zou Yongbing Xu Hua Wu Faxian Xiu State Key Laboratory of Surface Physics and Department of Physics Fudan University Institute for Nanoelectronic Devices and Quantum Computing Fudan University Laboratory for Computational Physical Sciences (MOE) Fudan University Department of Electronic Engineering Royal Holloway University of London School of Electronic Science and Engineering Nanjing University Materials Engineering The University of Queensland Department of Physics National University of Singapore Centre for Advanced 2D Materials and Graphene Research Centre National University of Singapore Lawrence Berkeley National Laboratory School of Information Science and Technology Shanghai Tech University Centre for Microscopy and Microanalysis The University of Queensland Collaborative Innovation Center of Advanced Microstructures

Mechanically exfoliated two-dimensional ferromagnetic materials(2 D FMs) possess long-range ferromagnetic order and topologically nontrivial skyrmions in few layers. However, because of the dimensionality effect, such few-layer systems usually exhibit much lower Curie temperature(TC) compared to their bulk counterparts. It is therefore of great interest to explore effective approaches to enhance their TC, particularly in wafer-scale for practical applications. Here, we report an interfacial proximity-induced high-TC2 D FM FeGe Te(FGT) via A-type antiferromagnetic material Cr Sb(CS) which strongly couples to FGT. A superlattice structure of(FGT/CS)n, where n stands for the period of FGT/CS heterostructure, has been successfully produced with sharp interfaces by molecular-beam epitaxy on 2-inch wafers. By performing elemental specific X-ray magnetic circular dichroism(XMCD) measurements, we have unequivocally discovered that TCof 4-layer FeGeTecan be significantly enhanced from 140 K to230 K because of the interfacial ferromagnetic coupling. Meanwhile, an inverse proximity effect occurs in the FGT/CS interface, driving the interfacial antiferromagnetic Cr Sb into a ferrimagnetic state as evidenced by double-switching behavior in hysteresis loops and the XMCD spectra. Density functional theory calculations show that the Fe-Te/Cr-Sb interface is strongly FM coupled and doping of the spin-polarized electrons by the interfacial Cr layer gives rise to the TCenhancement of the FeGeTefilms, in accordance with our XMCD measurements. Strikingly, by introducing rich Fe in a 4-layer FGT/CS superlattice, TCcan be further enhanced to near room temperature. Our results provide a feasible approach for enhancing the magnetic order of few-layer 2 D FMs in wafer-scale and render opportunities for realizing realistic ultra-thin spintronic devices.

关键词： 2D ferromagnetic material room temperature 2-inch Fe3GeTe2 film wafers proximity effect (Fe3GeTe2/CrSb)nsuperlattice

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A Novel Application of quantum Speed Limit to String Theory

arXiv

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arXiv 2023年

作者： Shabir, Arshid Wani, Salman Sajad Ali, Raja Nisar Kannan, S. Sheikh, Aasiya Faizal, Mir Sheikh, Javid A. Rubab, Seemin Al-Kuwari, Saif Department of Physics National Institute of Technology Srinagar190006 India Department of Physics University of Kashmir Srinagar190006 India Department of Physics Central University of Kashmir Tulmulla Ganderbal191131 India Qatar Center for Quantum Computing College of Science and Engineering Hamad Bin Khalifa University Qatar ISRO Inertial Systems Unit Thiruvananthapuram695013 India Design and Manufacturing Technology Division Raja Ramanna Centre for Advanced Technology Indore452013 India Canadian Quantum Research Center 204-3002 32 Ave VernonBCV1T 2L7 Canada Irving K. Barber School of Arts and Sciences University of British Columbia Okanagan KelownaBCV1V 1V7 Canada

In this work, we investigate the implications of the concept of quantum speed limit in string field theory. We adopt a novel approach to the problem of time on world-sheet based on Fisher information, and arrive at a minimum time for a particle state to evolve into another particle state. This is done using both the Mandelstam-Tamm bound and the Margolus-Levitin bound. This implies that any interaction has to be smeared over such an interval, and any interaction in the effective quantum field theory has to be non-local. As non-local quantum field theories are known to be finite, it is expected that divergences should be removed from effective quantum field theories due to the quantum speed limit of string theory. © 2023, CC BY.

关键词： String theory

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