Quantum natural gradient without monotonicity
Toi Sasaki, Hideyuki Miyahara
Physical Review A, 110, 2, American Physical Society (APS), 2024年08月27日
研究論文（学術雑誌）

Information geometric bound on general chemical reaction networks
Tsuyoshi Mizohata, Tetsuya J. Kobayashi, Louis-S. Bouchard, Hideyuki Miyahara
Physical Review E, 109, 4, American Physical Society (APS), 2024年04月11日
研究論文（学術雑誌）

Emergent invariance and scaling properties in the collective return dynamics of a stock market
Hideyuki Miyahara, Hai Qian, Pavan S. Holur, Vwani Roychowdhury
PLOS ONE, 19, 2, e0298789, e0298789, Public Library of Science (PLoS), 2024年02月23日
研究論文（学術雑誌）, A key metric to determine the performance of a stock in a market is its return over different investment horizons (τ). Several works have observed heavy-tailed behavior in the distributions of returns in different markets, which are observable indicators of underlying complex dynamics. Such prior works study return distributions that are marginalized across the individual stocks in the market, and do not track statistics about the joint distributions of returns conditioned on different stocks, which would be useful for optimizing inter-stock asset allocation strategies. As a step towards this goal, we study emergent phenomena in the distributions of returns as captured by their pairwise correlations. In particular, we consider the pairwise (between stocks i, j) partial correlations of returns with respect to the market mode, c_i,j(τ), (thus, correcting for the baseline return behavior of the market), over different time horizons (τ), and discover two novel emergent phenomena: (i) the standardized distributions of the c_i,j(τ)’s are observed to be invariant of τ ranging from from 1000min (2.5 days) to 30000min (2.5 months); (ii) the scaling of the standard deviation of c_i,j(τ)’s with τ admits good fits to simple model classes such as a power-law τ^−λ or stretched exponential function (λ, β > 0). Moreover, the parameters governing these fits provide a summary view of market health: for instance, in years marked by unprecedented financial crises—for example 2008 and 2020—values of λ (scaling exponent) are substantially lower. Finally, we demonstrate that the observed emergent behavior cannot be adequately supported by existing generative frameworks such as single- and multi-factor models. We introduce a promising agent-based Vicsek model that closes this gap.

Quantum advantage in variational Bayes inference
Hideyuki Miyahara, Vwani Roychowdhury
Proceedings of the National Academy of Sciences, 120, 31, Proceedings of the National Academy of Sciences, 2023年07月25日
研究論文（学術雑誌）, Variational Bayes (VB) inference algorithm is used widely to estimate both the parameters and the unobserved hidden variables in generative statistical models. The algorithm—inspired by variational methods used in computational physics—is iterative and can get easily stuck in local minima, even when classical techniques, such as deterministic annealing (DA), are used. We study a VB inference algorithm based on a nontraditional quantum annealing approach—referred to as quantum annealing variational Bayes (QAVB) inference—and show that there is indeed a quantum advantage to QAVB over its classical counterparts. In particular, we show that such better performance is rooted in key quantum mechanics concepts: i) The ground state of the Hamiltonian of a quantum system—defined from the given data—corresponds to an optimal solution for the minimization problem of the variational free energy at very low temperatures; ii) such a ground state can be achieved by a technique paralleling the quantum annealing process; and iii) starting from this ground state, the optimal solution to the VB problem can be achieved by increasing the heat bath temperature to unity, and thereby avoiding local minima introduced by spontaneous symmetry breaking observed in classical physics based VB algorithms. We also show that the update equations of QAVB can be potentially implemented using ⌈log K ⌉ qubits and ��( K ) operations per step, where K is the number of values hidden categorical variables can take. Thus, QAVB can match the time complexity of existing VB algorithms, while delivering higher performance.

Decoherence mitigation by embedding a logical qubit in a qudit
Hideyuki Miyahara, Yiyou Chen, Vwani Roychowdhury, Louis-Serge Bouchard
Quantum Information Processing, 22, 7, Springer Science and Business Media LLC, 2023年07月11日
研究論文（学術雑誌）, Abstract

Quantum information stored in a qubit is rapidly lost to the environment. The realization of robust qubits is one of the most important challenges in quantum computing. Herein, we propose to embed a logical qubit within the manifold of a qudit as a scheme to preserve quantum information over extended periods of time. Under identical conditions (e.g., decoherence channels), the submanifold of the logical qubit exhibits extended lifetimes compared to a pure two-level system (qubit). The retention of quantum information further improves with separation between the sublevels of the logical qubit. Lifetime enhancement can be understood in terms of entropy production of the encoding and nonencoding subspaces during evolution under a quantum map for ad-level system. The additional pathways for coherent evolution through intermediate sublevels within ad-level manifold provide an information-preserving mechanism: reversible alternative channels to the irreversible loss of information to the environment characteristic of open quantum systems.

Ansatz-Independent Variational Quantum Classifiers and the Price of Ansatz
Hideyuki Miyahara, Vwani Roychowdhury
Scientific Reports, 12, 1, Springer Science and Business Media LLC, 2022年11月14日
研究論文（学術雑誌）, Abstract

The paradigm of variational quantum classifiers (VQCs) encodes classical information as quantum states, followed by quantum processing and then measurements to generate classical predictions. VQCs are promising candidates for efficient utilizations of noisy intermediate scale quantum (NISQ) devices: classifiers involving M-dimensional datasets can be implemented with only $$\lceil \log _2 M \rceil $$ qubits by using an amplitude encoding. A general framework for designing and training VQCs, however, is lacking. An encouraging specific embodiment of VQCs, quantum circuit learning (QCL), utilizes an ansatz: a circuit with a predetermined circuit geometry and parametrized gates expressing a time-evolution unitary operator; training involves learning the gate parameters through a gradient-descent algorithm where the gradients themselves can be efficiently estimated by the quantum circuit. The representational power of QCL, however, depends strongly on the choice of the ansatz, as it limits the range of possible unitary operators that a VQC can search over. Equally importantly, the landscape of the optimization problem may have challenging properties such as barren plateaus and the associated gradient-descent algorithm may not find good local minima. Thus, it is critically important to estimate (i) the price of ansatz; that is, the gap between the performance of QCL and the performance of ansatz-independent VQCs, and (ii) the price of using quantum circuits as classical classifiers: that is, the performance gap between VQCs and equivalent classical classifiers. This paper develops a computational framework to address both these open problems. First, it shows that VQCs, including QCL, fit inside the well-known kernel method. Next it introduces a framework for efficiently designing ansatz-independent VQCs, which we call the unitary kernel method (UKM). The UKM framework enables one to estimate the first known computationally-determined bounds on both the price of ansatz and the price of any speedup advantages of VQCs: numerical results with datatsets of various dimensions, ranging from 4 to 256, show that the ansatz-induced gap can vary between 10 and 20$$\%$$, while the VQC-induced gap (between VQC and kernel method) can vary between 10 and 16$$\%$$. To further understand the role of ansatz in VQCs, we also propose a method of decomposing a given unitary operator into a quantum circuit, which we call the variational circuit realization (VCR): given any parameterized circuit block (as for example, used in QCL), it finds optimal parameters and the number of layers of the circuit block required to approximate any target unitary operator with a given precision.

Quantum approximation of normalized Schatten norms and applications to learning
Yiyou Chen, Hideyuki Miyahara, Louis-S. Bouchard, Vwani Roychowdhury
Physical Review A, 106, 5, American Physical Society (APS), 2022年11月09日
研究論文（学術雑誌）

Steady-state thermodynamics for population dynamics in fluctuating environments with side information
Hideyuki Miyahara
JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT, 2022, 1, 2022年01月
英語, 研究論文（学術雑誌）

Deterministic quantum annealing expectation-maximization algorithm (vol 11, 113404, 2017)
Hideyuki Miyahara, Koji Tsumura, Yuki Sughiyama
JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT, 2020, 10, 2020年10月
英語

Quantum expectation-maximization algorithm
Hideyuki Miyahara, Kazuyuki Aihara, Wolfgang Lechner
PHYSICAL REVIEW A, 101, 1, 2020年01月
英語, 研究論文（学術雑誌）

Many-body perturbation theory and fluctuation relations for interacting population dynamics
Hideyuki Miyahara
PHYSICAL REVIEW E, 99, 4, 2019年04月
英語, 研究論文（学術雑誌）

Work relations with measurement and feedback control on nonuniform temperature systems
Hideyuki Miyahara, Kazuyuki Aihara
PHYSICAL REVIEW E, 98, 4, 2018年10月
英語, 研究論文（学術雑誌）

Quantum extension of variational Bayes inference
Hideyuki Miyahara, Yuki Sughiyama
PHYSICAL REVIEW A, 98, 2, 2018年08月
英語, 研究論文（学術雑誌）

Deterministic quantum annealing expectation-maximization algorithm
Hideyuki Miyahara, Koji Tsumura, Yuki Sughiyama
JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT, 2017年11月
英語, 研究論文（学術雑誌）

Relaxation of the EM Algorithm via Quantum Annealing
Hideyuki Miyahara, Koji Tsumura
2016 AMERICAN CONTROL CONFERENCE (ACC), 4779, 4784, 2016年
英語, 研究論文（国際会議プロシーディングス）

Relaxation of the EM Algorithm via Quantum Annealing for Gaussian Mixture Models
Hideyuki Miyahara, Koji Tsumura, Yuki Sughiyama
2016 IEEE 55TH CONFERENCE ON DECISION AND CONTROL (CDC), 4674, 4679, 2016年
英語, 研究論文（国際会議プロシーディングス）

Development of a two-particle self-consistent method for multiorbital systems and its application to unconventional superconductors
Hideyuki Miyahara, Ryotaro Arita, Hiroaki Ikeda
PHYSICAL REVIEW B, 87, 4, 2013年01月
英語, 研究論文（学術雑誌）

Octet-Line Node Structure of Superconducting Order Parameter in KFe ₂ As ₂
K. Okazaki, Y. Ota, Y. Kotani, W. Malaeb, Y. Ishida, T. Shimojima, T. Kiss, S. Watanabe, C.-T. Chen, K. Kihou, C. H. Lee, A. Iyo, H. Eisaki, T. Saito, H. Fukazawa, Y. Kohori, K. Hashimoto, T. Shibauchi, Y. Matsuda, H. Ikeda, H. Miyahara, R. Arita, A. Chainani, S. Shin
Science, 337, 6100, 1314, 1317, American Association for the Advancement of Science (AAAS), 2012年09月14日
研究論文（学術雑誌）, An Eight-Noded Monster

In superconductors, electrons are bound into pairs, and the exact form of that pairing and the resulting energy gap can vary, depending on the details of the electron-electron interaction and the band structure of the material. The energy gaps of the recently discovered iron-based superconductors exhibit a variety of pairing functions. KFe ₂ As ₂ has been suggested to have a d -wave gap, similar to cuprate superconductors. Okazaki et al. (p. 1314 ) use laser-based angle-resolved photoemission spectroscopy (ARPES) to map out the superconducting gap on three Fermi surfaces (FS) of the compound. They find a different gap structure on each, with the middle FS gap vanishing at eight distinct positions (nodes). It appears that the gap respects the tetragonal symmetry of the crystal, indicating (although the details may vary) the all iron-based superconductors have an extended s -wave–symmetric pairing—a finding that will help understanding of unconventional superconductivity.

Rotation of multi-zeros optical beam during propagation and its application to distance measurement　　　　　　　　　　　　　　　
Hideyuki Miyahara, Yulan Qi, Toru Kurihara, Shigeru Ando
2011年09月, ［査読有り］, ［筆頭著者］
英語, 研究論文（国際会議プロシーディングス）

Vicsek Model Meets DBSCAN: Cluster Phases in the Vicsek Model
Hideyuki Miyahara, Hyu Yoneki, Vwani Roychowdhury, 2023年07月24日
The Vicsek model, which was originally proposed to explain the dynamics of
bird flocking, exhibits a phase transition with respect to the absolute value
of the mean velocity. Although clusters of agents can be easily observed via
numerical simulations of the Vicsek model, qualitative studies are lacking. We
study the clustering structure of the Vicsek model by applying DBSCAN, a
recently-introduced clustering algorithm, and report that the Vicsek model
shows a phase transition with respect to the number of clusters: from O(N) to
O(1), with N being the number of agents, when increasing the magnitude of noise
for a fixed radius that specifies the interaction of the Vicsek model. We also
report that the combination of the order parameter proposed by Vicsek et al.
and the number of clusters defines at least four phases of the Vicsek model.

27aBG-11 Two-Particle Self-Consistent Methodの多軌道系への拡張(27aBG 電子系(第一原理計算・非平衡系・電子相関),領域11(統計力学,物性基礎論,応用数学,力学,流体物理))
宮原 英之, 有田 亮太郎, 池田 裕章, 日本物理学会講演概要集, 67, 0, 373, 373, 2012年
一般社団法人 日本物理学会, 日本語

18pFF-17 鉄系超伝導体の2体自己無〓着法による解析(18pFF 鉄砒素系1(122系:置換効果・その他,理論),領域8(強相関係:高温超伝導,強相関f電子系など))
宮原 英之, 有田 亮太郎, 池田 浩章, 日本物理学会講演概要集, 67, 0, 460, 460, 2012年
一般社団法人 日本物理学会, 日本語