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Lieb-Robinson Light Cone for Power-Law Interactions

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Physical Review Letters 2021年第16期127卷 160401-160401页

作者： Minh C. Tran Andrew Y. Guo Christopher L. Baldwin Adam Ehrenberg Alexey V. Gorshkov Andrew Lucas Joint Center for Quantum Information and Computer Science NIST/University of Maryland College Park Maryland 20742 USA Joint Quantum Institute NIST/University of Maryland College Park Maryland 20742 USA Department of Physics University of Colorado Boulder Colorado 80309 USA Center for Theory of Quantum Matter University of Colorado Boulder Colorado 80309 USA

The Lieb-Robinson theorem states that information propagates with a finite velocity in quantum systems on a lattice with nearest-neighbor interactions. What are the speed limits on information propagation in quantum systems with power-law interactions, which decay as 1/rα at distance r? Here, we present a definitive answer to this question for all exponents α>2d and all spatial dimensions d. Schematically, information takes time at least rmin{1,α−2d} to propagate a distance r. As recent state transfer protocols saturate this bound, our work closes a decades-long hunt for optimal Lieb-Robinson bounds on quantum information dynamics with power-law interactions.

关键词： Dipolar interaction Mathematical physics quantum communication quantum information processing quantum state transfer Lattice models in statistical physics

Distributed Shor’s algorithm

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arXiv 2022年

作者： Xiao, Ligang Qiu, Daowen Luo, Le Mateus, Paulo Institute of Quantum Computing and Computer Theory School of Computer Science and Engineering Sun Yat-sen University Guangzhou510006 China School of Physics and Astronomy Sun Yat-sen University Zhuhai519082 China QUDOOR Technologies Inc. Guangzhou China Instituto de Telecomunicações Departamento de Matemática Instituto Superior Técnico Av. Rovisco Pais Lisbon1049-001 Portugal

Shor’s algorithm is one of the most important quantum algorithm proposed by Peter Shor [Proceedings of the 35th Annual Symposium on Foundations of computer science, 1994, pp. 124–134]. Shor’s algorithm can factor a large integer with certain probability and costs polynomial time in the length of the input integer. The key step of Shor’s algorithm is the order-finding algorithm. Specifically, given an L-bit integer N, we first randomly pick an integer a with gcd(a,N) = 1, the order of a modulo N is the smallest positive integer r such that ar ≡ 1(modN). The order-finding algorithm in Shor’s algorithm first uses quantum operations to obtain an estimation of s/r for some s ∈ {0,1,···,r − 1}, then r is obtained by means of classical algorithms. In this paper, we propose a distributed Shor’s algorithm. The difference between our distributed algorithm and the traditional order-finding algorithm is that we use two quantum computers separately to estimate partial bits of s/r for some s ∈ {0,1,···,r − 1}. To ensure their measuring results correspond to the same , we need employ quantum teleportation. We integrate the measuring results via classical post-processing. After that, we get an estimation of s/r with high precision. Compared with the r traditional Shor’s algorithm that uses multiple controlling qubits, our algorithm reduces nearly L/2 qubits and reduces the circuit depth of each computer. Copyright © 2022, The Authors. All rights reserved.

关键词： Qubits

Strong pulse illumination hacks self-differencing avalanche photodiode detectors in a high-speed quantum key distribution system

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arXiv 2022年

作者： Gao, Binwu Wu, Zhihao Shi, Weixu Liu, Yingwen Wang, Dongyang Yu, Chunlin Huang, Anqi Wu, Junjie Institute for Quantum Information State Key Laboratory of High Performance Computing College of Computer Science and Technology National University of Defense Technology Changsha410073 China China Greatwall Research Institute China Greatwall Technology Group CO. LTD. Shenzhen518057 China

Implementation of high-speed quantum key distribution (QKD) has become one of the major focuses in the field, which produces high key-generation rate for applications. To achieve high-speed QKD, tailored techniques are developed and employed to quickly generate and detect quantum states. However, these techniques may introduce unique loopholes to compromise the security of QKD systems. In this paper, we investigate the loopholes of self-differencing (SD) avalanche photodiode (APD) detector, typically used for high-speed detection in a QKD system, and demonstrate experimental testing of SD APD detector under strong pulse illumination attack. This attack presents blinding stability and helps an eavesdropper to learn the secret key without introducing extra QBER. Based on this testing, we propose a set of criteria for protecting SD APD detectors from the strong pulse illumination attack. Copyright © 2022, The Authors. All rights reserved.

关键词： Avalanche photodiodes

Perturbative quantum Simulation

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Physical Review Letters 2022年第12期129卷 120505-120505页

作者： Jinzhao Sun Suguru Endo Huiping Lin Patrick Hayden Vlatko Vedral Xiao Yuan Center on Frontiers of Computing Studies Peking University Beijing 100871 China Clarendon Laboratory University of Oxford Parks Road Oxford OX1 3PU United Kingdom Quantum Advantage Research Beijing 100080 China NTT Computer & Data Science Laboratories NTT corporation Musashino Tokyo 180-8585 Japan School of Computer Science Peking University Beijing 100871 China Stanford Institute for Theoretical Physics Stanford University Stanford California 94305 USA Centre for Quantum Technologies National University of Singapore Singapore 117543 Singapore

Approximation based on perturbation theory is the foundation for most of the quantitative predictions of quantum mechanics, whether in quantum many-body physics, chemistry, quantum field theory, or other domains. quantum computing provides an alternative to the perturbation paradigm, yet state-of-the-art quantum processors with tens of noisy qubits are of limited practical utility. Here, we introduce perturbative quantum simulation, which combines the complementary strengths of the two approaches, enabling the solution of large practical quantum problems using limited noisy intermediate-scale quantum hardware. The use of a quantum processor eliminates the need to identify a solvable unperturbed Hamiltonian, while the introduction of perturbative coupling permits the quantum processor to simulate systems larger than the available number of physical qubits. We present an explicit perturbative expansion that mimics the Dyson series expansion and involves only local unitary operations, and show its optimality over other expansions under certain conditions. We numerically benchmark the method for interacting bosons, fermions, and quantum spins in different topologies, and study different physical phenomena, such as information propagation, charge-spin separation, and magnetism, on systems of up to 48 qubits only using an 8+1 qubit quantum hardware. We demonstrate our scheme on the IBM quantum cloud, verifying its noise robustness and illustrating its potential for benchmarking large quantum processors with smaller ones.

关键词： quantum algorithms quantum computation quantum simulation

Hybrid Error-Management Strategies in quantum Repeater Networks

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arXiv 2023年

作者： Pathumsoot, Poramet Tansuwannont, Theerapat Benchasattabuse, Naphan Satoh, Ryosuke Hajdušek, Michal Chaiwongkhot, Poompong Suwanna, Sujin Van Meter, Rodney Optical and Quantum Physics Laboratory Department of Physics Faculty of Science Mahidol University Bangkok10400 Thailand Keio University Shonan Fujisawa Campus 5322 Endo Kanagawa Fujisawa252-0882 Japan Institute for Quantum Computing Department of Physics and Astronomy University of Waterloo WaterlooONN2L 3G1 Canada Duke Quantum Center Department of Electrical and Computer Engineering Duke University DurhamNC27708 United States National Astronomical Research Institute of Thailand Chiang Mai50180 Thailand Bangkok Thailand

A quantum network is expected to enhance distributed quantum computing and quantum communication over a long distance while providing unconditional security. As quantum entanglement is essential for a quantum network, major issues from various types of noise and decoherence prevent it from being realized, and research has been intensively active to obtain optimal configurations for a quantum network. In this work, we address the performance of a quantum network capable of quantum error correction and entanglement purification. Our results show that one should distribute Bell pairs as fast as possible while balancing the deployment of fidelity enhancement. We also show suitable hybrid strategies in quantum cryptography tasks under some noise regimes that need to use purification and quantum error correction together. Our results suggest that using purification to distribute high fidelity Bell pairs and preserving them for application using quantum error correction is a promising way to achieve a near-term quantum network for secure communication. Copyright © 2023, The Authors. All rights reserved.

关键词： Purification

Parallel repetition with a threshold in quantum interactive proofs

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arXiv 2020年

作者： Molina, Abel Institute for Quantum Computing School of Computer Science University of Waterloo Canada

In this note, we show that O(log(1/Ε )) rounds of parallel repetition with a threshold suffice to reduce completeness and soundness error to Ε for single-prover quantum interactive proof systems. This improves on a previous O(log(1/Ε) log log(1/Ε)) bound from Hornby (2018), while also simplifying its proof. A key element in our proof is a concentration bound from Impagliazzo and Kabanets (2010). Copyright © 2020, The Authors. All rights reserved.

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Pauli error estimation via Population Recovery

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arXiv 2021年

作者： Flammia, Steven T. O'Donnell, Ryan AWS Center for Quantum Computing United States IQIM California Institute of Technology United States Computer Science Department Carnegie Mellon University United States

Motivated by estimation of quantum noise models, we study the problem of learning a Pauli channel, or more generally the Pauli error rates of an arbitrary channel. By employing a novel reduction to the "Population Recovery" problem, we give an extremely simple algorithm that learns the Pauli error rates of an n-qubit channel to precision ∊ in ∞ using just O(1/∊2) log(n/∊) applications of the channel. This is optimal up to the logarithmic factors. Our algorithm uses only unentangled state preparation and measurements, and the post-measurement classical runtime is just an O(1/∊) factor larger than the measurement data size. It is also impervious to a limited model of measurement noise where heralded measurement failures occur independently with probability ≤ 1/4. We then consider the case where the noise channel is close to the identity, meaning that the no-error outcome occurs with probability 1 − η. In the regime of small η we extend our algorithm to achieve multiplicative precision 1 ± ∊ (i.e., additive precision ∊η) using just O(1/∊2η) log(n/∊) applications of the channel. © 2021, CC BY-SA.

关键词： quantum noise

CubeSat single-photon detector module for investigating in-orbit laser annealing to heal radiation damage

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arXiv 2024年

作者： Sultana, Nigar Krynski, Joanna Lim, Jin Gyu Floyd, John Lembeck, Michael Makarov, Vadim Kwiat, Paul Jennewein, Thomas Institute for Quantum Computing University of Waterloo WaterlooONN2L 3G1 Canada Department of Electrical and Computer Engineering University of Waterloo WaterlooONN2L 3G1 Canada Department of Physics and Astronomy University of Waterloo WaterlooONN2L 3G1 Canada University of Illinois Urbana-Champaign ChampaignIL United States Vigo Quantum Communication Center University of Vigo Vigo Spain Quantum Information Science Program Canadian Institute for Advanced Research TorontoONM5G 1Z8 Canada

Single-photon avalanche photodiodes (SPADs) based on silicon are widely considered for quantum satellite communications but suffer from an increasing dark count rate (DCR) due to displacement damage in their active areas induced by proton radiation. When the DCR of SPADs exceeds a certain threshold, they become unusable for quantum communication protocols. Previous laboratory experiments have demonstrated that laser annealing of SPADs’ active area with about 1 W optical power can significantly reduce radiation-induced DCR of synthetically irradiated SPADs. To assess the feasibility of in-orbit laser annealing on constantly irradiated SPADs in low-Earth orbit, we developed a module with a CubeSat form factor capable of both laser and thermal annealing of four silicon SPADs. Here we report the design and ground testing of this module, investigating laser annealing in a simulated space environment. Our results pave the way for an in-orbit trial that may prove this technology useful for future satellite missions with quantum receivers on board. Copyright © 2024, The Authors. All rights reserved.

关键词： Radiation damage

Complexity limitations on one-turn quantum refereed games

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arXiv 2020年

作者： Ghosh, Soumik Watrous, John Institute for Quantum Computing School of Computer Science University of Waterloo Canada

This paper studies complexity theoretic aspects of quantum refereed games, which are abstract games between two competing players that send quantum states to a referee, who performs an efficiently implementable joint measurement on the two states to determine which of the player wins. The complexity class QRG(1) contains those decision problems for which one of the players can always win with high probability on yes-instances and the other player can always win with high probability on no-instances, regardless of the opposing player’s strategy. This class trivially contains QMA ∪ co-QMA and is known to be contained in PSPACE. We prove stronger containments on two restricted variants of this class. Specifically, if one of the players is limited to sending a classical (probabilistic) state rather than a quantum state, the resulting complexity class CQRG(1) is contained in ∃ · PP (the nondeterministic polynomial-time operator applied to PP);while if both players send quantum states but the referee is forced to measure one of the states first, and incorporates the classical outcome of this measurement into a measurement of the second state, the resulting class MQRG(1) is contained in P · PP (the unbounded-error probabilistic polynomial-time operator applied to PP). Copyright © 2020, The Authors. All rights reserved.

关键词： Computational complexity