Updated on 2025/06/29

写真a

 
TAJIMA HIROYASU
 
Organization
Faculty of Information Science and Electrical Engineering Department of Informatics Associate Professor
Joint Graduate School of Mathematics for Innovation (Concurrent)
Graduate School of Information Science and Electrical Engineering Department of Information Science and Technology(Concurrent)
School of Engineering Department of Electrical Engineering and Computer Science(Concurrent)
Title
Associate Professor

Papers

  • Gibbs-Preserving Operations Requiring Infinite Amount of Quantum Coherence Reviewed

    Tajima, H; Takagi, R

    PHYSICAL REVIEW LETTERS   134 ( 17 )   2025.4   ISSN:0031-9007 eISSN:1079-7114

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    Authorship:Lead author, Last author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Physical Review Letters  

    Gibbs-preserving operations have been studied as one of the standard free processes in quantum thermodynamics. Although they admit a simple mathematical structure, their operational significance has been unclear due to the potential hidden cost to implement them using an operationally motivated class of operations, such as thermal operations. Here, we show that this hidden cost can be infinite - we present a family of Gibbs-preserving operations that cannot be implemented by thermal operations aided by any finite amount of quantum coherence. Our result implies that there are uncountably many Gibbs-preserving operations that require unbounded thermodynamic resources to implement, raising a question about employing Gibbs-preserving operations as available thermodynamics processes. This finding is a consequence of the general lower bounds we provide for the coherence cost of approximately implementing a certain class of Gibbs-preserving operations with a desired accuracy. We find that our lower bound is almost tight, identifying a quantity - related to the energy change caused by the channel to implement - as a fundamental quantifier characterizing the coherence cost for the approximate implementation of Gibbs-preserving operations.

    DOI: 10.1103/PhysRevLett.134.170201

    Web of Science

    Scopus

    PubMed

  • Symmetry Induced Enhancement in Finite-Time Thermodynamic Trade-Off Relations Reviewed

    Funo K., Tajima H.

    Physical Review Letters   134 ( 8 )   2025.2   ISSN:00319007

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Physical Review Letters  

    Symmetry imposes constraints on open quantum systems, affecting the dissipative properties in nonequilibrium processes. Superradiance is a typical example in which the decay rate of the system is enhanced via a collective system-bath coupling that respects permutation symmetry. Such a model has also been applied to heat engines. However, a generic framework that addresses the impact of symmetry in finite-time thermodynamics is not well established. Here, we show a symmetry-based framework that describes the fundamental limit of collective enhancement in finite-time thermodynamics. Specifically, we derive a general upper bound on the average jump rate, which quantifies the fundamental speed set by thermodynamic speed limits and trade-off relations. We identify the symmetry condition that achieves the obtained bound, and explicitly construct an open quantum system model that goes beyond the enhancement realized by the conventional superradiance model.

    DOI: 10.1103/PhysRevLett.134.080401

    Scopus

  • Universal Sampling Lower Bounds for Quantum Error Mitigation

    Takagi R., Tajima H., Gu M.

    Physical Review Letters   131 ( 21 )   2023.11   ISSN:00319007

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    Publisher:Physical Review Letters  

    Numerous quantum error-mitigation protocols have been proposed, motivated by the critical need to suppress noise effects on intermediate-scale quantum devices. Yet, their general potential and limitations remain elusive. In particular, to understand the ultimate feasibility of quantum error mitigation, it is crucial to characterize the fundamental sampling cost - how many times an arbitrary mitigation protocol must run a noisy quantum device. Here, we establish universal lower bounds on the sampling cost for quantum error mitigation to achieve the desired accuracy with high probability. Our bounds apply to general mitigation protocols, including the ones involving nonlinear postprocessing and those yet to be discovered. The results imply that the sampling cost required for a wide class of protocols to mitigate errors must grow exponentially with the circuit depth for various noise models, revealing the fundamental obstacles in the scalability of useful noisy near-term quantum devices.

    DOI: 10.1103/PhysRevLett.131.210602

    Scopus

  • Wigner-Araki-Yanase Theorem for Continuous and Unbounded Conserved Observables

    Kuramochi, Y; Tajima, H

    PHYSICAL REVIEW LETTERS   131 ( 21 )   210201   2023.11   ISSN:0031-9007 eISSN:1079-7114

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    Language:English   Publisher:Physical Review Letters  

    The Wigner-Araki-Yanase (WAY) theorem states that additive conservation laws imply the commutativity of exactly implementable projective measurements and the conserved observables of the system. Known proofs of this theorem are only restricted to bounded or discrete-spectrum conserved observables of the system and are not applicable to unbounded and continuous observables like a momentum operator. In this Letter, we present the WAY theorem for possibly unbounded and continuous conserved observables under the Yanase condition, which requires that the probe positive operator-valued measure should commute with the conserved observable of the probe system. As a result of this WAY theorem, we show that exact implementations of the projective measurement of the position under momentum conservation and of the quadrature amplitude using linear optical instruments and photon counters are impossible. We also consider implementations of unitary channels under conservation laws and find that the conserved observable LS of the system commutes with the implemented unitary US if LS is semibounded, while US†LSUS can shift up to possibly nonzero constant factor if the spectrum of LS is upper and lower unbounded. We give simple examples of the latter case, where LS is a momentum operator.

    DOI: 10.1103/PhysRevLett.131.210201

    Web of Science

    Scopus

    PubMed

  • Beyond i.i.d. in the Resource Theory of Asymmetry: An Information-Spectrum Approach for Quantum Fisher Information

    Yamaguchi K., Tajima H.

    Physical Review Letters   131 ( 20 )   2023.11   ISSN:00319007

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    Publisher:Physical Review Letters  

    Energetic coherence is indispensable for various operations, including precise measurement of time and acceleration of quantum manipulations. Since energetic coherence is fragile, it is essential to understand the limits in distillation and dilution to restore damage. The resource theory of asymmetry (RTA) provides a rigorous framework to investigate energetic coherence as a resource to break time-translation symmetry. Recently, in the independent and identically distributed (i.i.d.) regime where identical copies of a state are converted into identical copies of another state, it was shown that the convertibility of energetic coherence is governed by a standard measure of energetic coherence, called the quantum Fisher information (QFI). This fact means that QFI in the theory of energetic coherence takes the place of entropy in thermodynamics and entanglement entropy in entanglement theory. However, distillation and dilution in realistic situations take place in regimes beyond i.i.d., where quantum states often have complex correlations. Unlike entanglement theory, the conversion theory of energetic coherence in pure states in the non-i.i.d. regime has been an open problem. In this Letter, we solve this problem by introducing a new technique: an information-spectrum method for QFI. Two fundamental quantities, coherence cost and distillable coherence, are shown to be equal to the spectral QFI rates for arbitrary sequences of pure states. As a consequence, we find that both entanglement theory and RTA in the non-i.i.d. regime are understood in the information-spectrum method, while they are based on different quantities, i.e., entropy and QFI, respectively.

    DOI: 10.1103/PhysRevLett.131.200203

    Scopus

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Research Projects

  • Development and Application of a General Theory of Asymmetry Based on Resource Theory

    Grant number:25K00924  2025.4 - 2029.3

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (B)

    田島 裕康, 高木 隆司

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    Grant type:Scientific research funding

    現代物理において、対称性とその破れは最も基礎的な概念の一つである。近年、この概念をリソース理論的に取り扱う非対称性のリソース理論が、非常に大きな発展を遂げている。この理論は物理の様々な分野に応用されつつあるが、基礎理論が完成しているのが非常に限定的な群で表現される対称性に限られているという問題がある。本研究計画ではこの点を解決し、物性物理をはじめとした多くの対象に応用することを目指す。

  • Theory of performance enhancement of energy devices based on quantum effects

    Grant number:24H00831  2024.4 - 2027.3

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Transformative Research Areas (B)

    田島 裕康, 布能 謙

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    Grant type:Scientific research funding

    近年、量子力学の性質を用いて、計算やセンシングなどの様々な情報的タスクをオーダーレベルで性能向上させる「量子優位性」が確認されつつある。本計画班では、代表者・分担者が提案した量子効果による熱機関の性能の線形オーダーでの向上についての結果を発展させ、エネルギーデバイスに対する「量子優位性」の全貌を、より高次オーダーの性能向上の可能性を含めて明らかにする一般論を構築することを目的とする。合わせて、このような性能向上を活用し、理想的な熱・仕事変換効率と高出力を合わせ持つ熱機関を実験で実装するための理論提案を行う。

  • Pioneering and realizing innovative methods to improve the efficiency of energy gene ration/utilization through quantum effects

    Grant number:24H00830  2024.4 - 2027.3

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Transformative Research Areas (B)

    田島 裕康, 野口 篤史, 金澤 輝代士, 伊藤 創祐

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    Grant type:Scientific research funding

    本領域では、これまで計算や通信と言った情報分野で確認されてきた、量子効果による古典力学に従うデバイスに比べた飛躍的な性能上昇(量子優位性)がエネルギー生成・消費の分野にも存在する事を、理論的・実験的に検証することを目標としている。本総括班では、領域全体の運営・広報・領域内交流・webによる情報発信などを行う。