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Physical Review Applied 2023年第1期20卷 014057-014057页

作者： T. Yamaji S. Masuda A. Yamaguchi T. Satoh A. Morioka Y. Igarashi M. Shirane T. Yamamoto Secure System Platform Research Laboratories NEC Corporation Kawasaki Kanagawa 211-0011 Japan NEC-AIST Quantum Technology Cooperative Research Laboratory National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Ibaraki 305-8568 Japan Research Center for Emerging Computing Technologies (RCECT) National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Ibaraki 305-8568 Japan

We study simultaneous parametric oscillations in a system composed of two distributed-element-circuit Josephson parametric oscillators in the single-photon Kerr regime coupled via a static capacitance. The energy of the system is described by a two-bit Ising Hamiltonian with an effective coupling whose amplitude and sign depend on the relative phase between parametric pumps. We demonstrate that the binary phases of the parametric oscillations are correlated with each other, and that the parity and strength of the correlation can be controlled by adjusting the pump phase. The observed correlation is reproduced in our simulation taking pure dephasing into account. The present result demonstrates the tunability of the Hamiltonian parameters by the phase of external microwave, which can be used in the Ising machine hardware composed of the Kerr parametric oscillator network.

关键词： Adiabatic quantum optimization Optical quantum information processing Optoelectronics Superconducting quantum optics Optical parametric oscillators & amplifiers Ising model Microwave techniques

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Nonstoquastic catalyst for bifurcation-based quantum annealing of the ferromagnetic p-spin model

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Physical Review A 2023年第5期107卷 052401-052401页

作者： Yuki Susa Takashi Imoto Yuichiro Matsuzaki Secure System Platform Research Laboratories NEC Corporation Kawasaki Kanagawa 211-8666 Japan NEC-AIST Quantum Technology Cooperative Research Laboratory National Institute of Advanced Industrial Science and Technology Tsukuba Ibaraki 305-8568 Japan Research Center for Emerging Computing Technologies National Institute of Advanced Industrial Science and Technology 1-1-1 Umezono Tsukuba Ibaraki 305-8568 Japan

Introducing a nonstoquastic catalyst is a promising avenue to improve quantum annealing with the transverse field. In the present paper, we propose a nonstoquastic catalyst for bifurcation-based quantum annealing described by the spin-1 operators to improve the efficiency of a ground-state search. To investigate the effect of the nonstoquastic catalyst, we study the ferromagnetic p-spin model, which has difficulty with finding the ground state due to the first-order phase transition for quantum annealing. A semiclassical analysis shows that the problematic first-order phase transition can be eliminated by introducing the proposed nonstoquastic catalyst with the appropriate amplitude. We also numerically calculate the minimum energy gap for a finite-size system by diagonalizing the Hamiltonian. We find that while the energy gap decreases exponentially with increasing system size for the original Hamiltonian, it decreases polynomially against the system size for the Hamiltonian with the nonstoquastic catalyst. This result implies that the proposed nonstoquastic catalyst has the potential to improve the performance of bifurcation-based quantum annealing.

关键词： Adiabatic quantum optimization

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Guaranteed-accuracy quantum annealing

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Physical Review A 2022年第4期106卷 042615-042615页

作者： Takashi Imoto Yuya Seki Yuichiro Matsuzaki Shiro Kawabata Research Center for Emerging Computing Technologies (RCECT) National Institute of Advanced Industrial Science and Technology (AIST) 1-1-1 Umezono Tsukuba Ibaraki 305-8568 Japan NEC-AIST Quantum Technology Cooperative Research Laboratory National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Ibaraki 305-8568 Japan

quantum chemistry calculations constitute an important application of quantum annealing (QA). For practical applications in quantum chemistry, it is essential to estimate the ground-state energy of the Hamiltonian with chemical accuracy. However, there is no known method for guaranteeing the accuracy of the energy estimated via QA. Here, we propose a method for guaranteeing the accuracy of the energy estimated via QA using the Weinstein and Temple bounds. In our scheme, before QA is performed, the energies of the ground state and first excited state must be preestimated with some error bars (corresponding to the possible estimation error) via classical computation with some approximations. We show that, if the expectation value and standard deviation of the energy of the state after QA are lower than certain threshold values (that we can calculate from the preestimation), the ground-state energy estimated by QA is closer to the ground-state energy than the preestimation. As the expectation value and standard deviation of the energy can be experimentally measured via QA, our results pave the way for accurate estimation of the ground-state energy using QA.

关键词： Adiabatic quantum optimization quantum computation

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Adaptive measurement strategy for noisy quantum amplitude estimation with variational quantum circuits

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Physical Review A 2024年第6期110卷 062423-062423页

作者： Kohei Oshio Yohichi Suzuki Kaito Wada Keigo Hisanaga Shumpei Uno Naoki Yamamoto Mizuho Research & Technologies Ltd. 2-3 Kandanishiki Chiyoda-ku Tokyo 100-8233 Japan Quantum Computing Center Keio University 3-14-1 Hiyoshi Kohoku-ku Yokohama Kanagawa 223-8522 Japan Global Research and Development Center for Business by Quantum-AI Technology (G-QuAT) National Institute of Advanced Industrial Science and Technology (AIST) 1-1-1 Umezono Tsukuba-shi Ibaraki 305-8568 Japan Department of Applied Physics and Physico-Informatics Keio University Hiyoshi 3-14-1 Kohoku-ku Yokohama 223-8522 Japan

In quantum computation, amplitude estimation is a fundamental subroutine that is utilized in various quantum algorithms. A general important task of such estimation problems is to characterize the estimation lower bound, which is referred to as quantum Cramér-Rao bound (QCRB), and to construct an optimal estimator that achieves QCRB. This paper studies the amplitude estimation in the presence of depolarizing noise with unknown intensity. The main difficulty in this problem is that the optimal measurement depends on both the unknown quantum state and the amplitude we aim to estimate. To deal with these issues, we utilize the variational quantum circuits to approximate the (unknown) optimal measurement basis combined with the two-step adaptive estimation strategy which was proposed in the quantum estimation theory. We numerically show that the proposed method can nearly attain the QCRB.

关键词： quantum computers

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Method to deterministically generate large-amplitude optical cat states

arXiv

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arXiv 2023年

作者： Li, Zheng-Hong Yu, Fei Li, Zhen-Ya Al-Amri, M. Zubairy, M. Suhail Institute for Quantum Science and Technology Department of Physics Shanghai University Shanghai200444 China Shanghai Key Laboratory of High Temperature Superconductors Shanghai University Shanghai200444 China Department of Physics and Astronomy Texas A&M University College StationTX77843-4242 United States NCQOQI KACST P.O.Box 6086 Riyadh11442 Saudi Arabia Institute of Quantum Technologies and Advanced Computing KACST Riyadh11442 Saudi Arabia

Cat states, as an important resource in the study of macroscopic quantum superposition and quantum information applications, have garnered widespread attention. To date, preparing large-sized optical cat states has remained challenging. We demonstrate that, by utilizing interaction-free measurement and the quantum Zeno effect, even a fragile quantum microscopic system can deterministically control and become entangled with strong light fields, thereby generating large-amplitude optical cat states. During the entire preparation process, our method ensures that the microscopic system functions within a weak field environment, so that its quantum property can be protected. Furthermore, we show that the preparation of cat states is possible even when the quantum microsystem suffers from significant photon loss, provided that optical losses from classical devices are kept low, which implies that the fidelity of the cat state can be enhanced by improvements to and the perfection of the classical optical system. Copyright © 2023, The Authors. All rights reserved.

关键词： Optical systems

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Error-Mitigated quantum Metrology via Virtual Purification

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Physical Review Letters 2022年第25期129卷 250503-250503页

作者： Kaoru Yamamoto Suguru Endo Hideaki Hakoshima Yuichiro Matsuzaki Yuuki Tokunaga NTT Computer and Data Science Laboratories NTT Corporation Musashino 180-8585 Japan JST PRESTO 4-1-8 Honcho Kawaguchi Saitama 332-0012 Japan Research Center for Emerging Computing Technologies National Institute of Advanced Industrial Science and Technology (AIST) Central2 1-1-1 Umezono Tsukuba Ibaraki 305-8568 Japan Center for Quantum Information and Quantum Biology Osaka University 1-2 Machikaneyama Toyonaka 560-0043 Japan NEC-AIST Quantum Technology Cooperative Research Laboratory National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Ibaraki 305-8568 Japan

quantum metrology with entangled resources aims to achieve sensitivity beyond the standard quantum limit by harnessing quantum effects even in the presence of environmental noise. So far, sensitivity has been mainly discussed from the viewpoint of reducing statistical errors under the assumption of perfect knowledge of a noise model. However, we cannot always obtain complete information about a noise model due to coherence time fluctuations, which are frequently observed in experiments. Such unknown fluctuating noise leads to systematic errors and nullifies the quantum advantages. Here, we propose an error-mitigated quantum metrology that can filter out unknown fluctuating noise with the aid of purification-based quantum error mitigation. We demonstrate that our protocol mitigates systematic errors and recovers superclassical scaling in a practical situation with time-inhomogeneous bias-inducing noise. Our result is the first demonstration to reveal the usefulness of purification-based error mitigation for unknown fluctuating noise, thus paving the way not only for practical quantum metrology but also for quantum computation affected by such noise.

关键词： quantum algorithms quantum metrology quantum sensing quantum simulation

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Testing a quantum error-correcting code on various platforms

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Science Bulletin 2021年第1期66卷 29-35,M0003页

作者： Qihao Guo Yuan-Yuan Zhao Markus Grassl Xinfang Nie Guo-Yong Xiang Tao Xing Zhang-Qi Yin Bei Zeng Institute for Quantum Computing Baidu ResearchBeijing 100193China Department of Applied Physics Xi’an Jiaotong UniversityXi’an 710049China Center for Quantum Computing Peng Cheng LaboratoryShenzhen 518055China CAS Key Laboratory of Quantum Information University of Science and Technology of ChinaHefei 230026China Max Planck Institute for the Science of Light 91058 ErlangenGermany International Centre for Theory of Quantum Technologies 80-308 GdańskPoland Shenzhen Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and TechnologyShenzhen 518055China Guangdong Provincial Key Laboratory of Quantum Science and Engineering Southern University of Science and TechnologyShenzhen 518055China Center for Quantum Technology Research and Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurements(MOE) School of PhysicsBeijing Institute of TechnologyBeijing 100081China Department of Physics The Hong Kong University of Science and TechnologyHong KongChina.

quantum error correction plays an important role in fault-tolerant quantum information *** is usually difficult to experimentally realize quantum error correction,as it requires multiple qubits and quantum gates with high *** we propose a simple quantum error-correcting code for the detected amplitude damping *** code requires only two *** implement the encoding,the channel,and the recovery on an optical platform,the IBM Q System,and a nuclear magnetic resonance *** all of these systems,the error correction advantage appears when the damping rate exceeds some *** compare the features of these quantum information processing systems used and demonstrate the advantage of quantum error correction on current quantum computing platforms.

关键词： quantum error correction quantum computation Superconducting circuit NMR system Optical platform

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Scalable flux controllers using adiabatic superconductor logic for quantum processors

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Physical Review Research 2023年第1期5卷 013145-013145页

作者： Naoki Takeuchi Taiki Yamae Wenhui Luo Fuminori Hirayama Tsuyoshi Yamamoto Nobuyuki Yoshikawa Research Center for Emerging Computing Technologies National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Ibaraki 305-8568 Japan NEC-AIST Quantum Technology Cooperative Research Laboratory National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Ibaraki 305-8568 Japan Department of Electrical and Computer Engineering Yokohama National University Yokohama Kanagawa 240-8501 Japan Research Fellow of Japan Society for the Promotion of Science Chiyoda Tokyo 102-0083 Japan Secure System Platform Research Laboratories NEC Corporation Kawasaki Kanagawa 211-0011 Japan Institute of Advanced Sciences Yokohama National University Yokohama Kanagawa 240-8501 Japan

quantum processors have the potential to accelerate specific computing tasks but are difficult to scale up due to engineering limitations, such as the number of available cables and cooling power for dilution refrigerators for quantum bits (qubits). Hence, it is very important to develop scalable, energy-efficient interface circuits that can control many qubits via a few control lines inside a dilution refrigerator. One of the most important interface circuits is the flux controller (FC), which generates arbitrary dc flux bias to adjust the characteristics of component devices such as qubits. In this paper, we propose and demonstrate FCs using an energy-efficient superconductor logic family, adiabatic quantum-flux-parametron (AQFP) logic. We develop two types of FCs: the AQFP FC and the AQFP/single-flux-quantum (AQFP/SFQ) FC. Both FCs require only a few control lines and have extremely small power dissipation, thus exhibiting high scalability. Furthermore, the AQFP/SFQ FC can control flux bias using ballistic SFQ transmission, which is crucial for integration with qubits. As a proof of concept, we demonstrate AQFP and AQFP/SFQ FCs at 4.2 K, fabricated by the AIST high-speed standard process. Our results indicate that AQFP logic is highly suitable for use as qubit interface circuits for very large-scale quantum processors, especially from the viewpoint of the control line count, power dissipation, and amount of supply currents.

关键词： Engineering Devices for digital logic, storage & processing Josephson junctions SQUID Superconducting devices

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quantum-Enhanced Heat Engine Based on Superabsorption

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Physical Review Letters 2022年第18期128卷 180602-180602页

作者： Shunsuke Kamimura Hideaki Hakoshima Yuichiro Matsuzaki Kyo Yoshida Yasuhiro Tokura Research Center for Emerging Computing Technologies National Institute of Advanced Industrial Science and Technology (AIST) 1-1-1 Umezono Tsukuba Ibaraki 305-8568 Japan Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba 305-8571 Japan Center for Quantum Information and Quantum Biology Osaka University 1-2 Machikaneyama Toyonaka 560-0043 Japan Tsukuba Research Center for Energy Materials Science (TREMS) Tsukuba 305-8571 Japan

We propose a quantum-enhanced heat engine with entanglement. The key feature of our scheme is superabsorption, which facilitates enhanced energy absorption by entangled qubits. Whereas a conventional engine with N separable qubits provides power with a scaling of P=Θ(N), our engine uses superabsorption to provide power with a quantum scaling of P=Θ(N2). This quantum heat engine also exhibits a scaling advantage over classical ones composed of N-particle Langevin systems. Our work elucidates the quantum properties allowing for the enhancement of performance.

关键词： quantum control quantum entanglement quantum heat engines & refrigerators

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quantum State Tomography for Kerr Parametric Oscillators

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Physical Review Applied 2023年第3期20卷 034031-034031页

作者： Y. Suzuki S. Kawabata T. Yamamoto S. Masuda Department of Physics Faculty of Science Division I Tokyo University of Science 1-3 Kagurazaka Shinjuku-ku Tokyo 162-8601 Japan Research Center for Emerging Computing Technologies (RCECT) National Institute of Advanced Industrial Science and Technology (AIST) 1-1-1 Umezono Tsukuba Ibaraki 305-8568 Japan NEC-AIST Quantum Technology Cooperative Research Laboratory National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Ibaraki 305-8568 Japan System Platform Research Laboratories NEC Corporation Kawasaki Kanagawa 211-0011 Japan

Kerr parametric oscillators (KPOs) implemented in the circuit quantum electrodynamic architecture can operate as qubits. Their applications to quantum annealing and universal quantum computation have been studied intensively. For these applications, the readout of the state of KPOs is of practical importance. We develop a scheme of state tomography for KPOs with reflection measurement. Although it is known that the reflection coefficient depends on the state of the KPO, it is unclear whether tomography of a qubit encoded into a KPO can be performed in a practical way mitigating decoherence during the measurement, and how accurate it is. We show that the reflection coefficient has a one-to-one correspondence with a diagonal element of the density matrix of the qubit when a probe frequency is properly chosen and an additional single-photon drive is introduced. Thus, our scheme offers a novel way to read out the qubit along an axis of the Bloch sphere, and therefore the reflection measurement and single-qubit gates can constitute state tomography.

关键词： quantum circuits quantum measurements quantum tomography Optical parametric oscillators & amplifiers

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