Updated on 2025/03/18

写真a

 
KATO Kohtaro
 
Organization
Graduate School of Informatics Department of Mathematical Informatics 2 Assistant Professor
Graduate School
Graduate School of Informatics
Undergraduate School
School of Informatics Department of Natural Informatics
Title
Assistant Professor

Degree 1

  1. Ph.D. in Science ( 2017.3   The University of Tokyo ) 

 

Papers 16

  1. Universal validity of the second law of information thermodynamics

    Minagawa S., Mohammady M.H., Sakai K., Kato K., Buscemi F.

    npj Quantum Information   Vol. 11 ( 1 )   2025.12

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    Publisher:npj Quantum Information  

    Adiabatic measurements, followed by feedback and erasure protocols, have often been considered as a model to embody Maxwell’s Demon paradox and to study the interplay between thermodynamics and information processing. Such studies have led to the conclusion, now widely accepted in the community, that Maxwell’s Demon and the second law of thermodynamics can peacefully coexist because any gain provided by the demon must be offset by the cost of performing the measurement and resetting the demon’s memory to its initial state. Statements of this kind are collectively referred to as second laws of information thermodynamics and have recently been extended to include quantum theoretical scenarios. However, previous studies in this direction have made several assumptions, particularly about the feedback process and the demon’s memory readout, and thus arrived at statements that are not universally applicable and whose range of validity is not clear. In this work, we fill this gap by precisely characterizing the full range of quantum feedback control and erasure protocols that are overall consistent with the second law of thermodynamics. This leads us to conclude that the second law of information thermodynamics is indeed universal: it must hold for any quantum feedback control and erasure protocol, regardless of the measurement process involved, as long as the protocol is overall compatible with thermodynamics. Our comprehensive analysis not only encompasses new scenarios but also retrieves previous ones, doing so with fewer assumptions. This simplification contributes to a clearer understanding of the theory.

    DOI: 10.1038/s41534-024-00922-w

    Scopus

  2. Port-based telecloning of an unknown quantum state

    Reiji Okada, Kohtaro Kato, Francesco Buscemi

    arXiv e-print     2025.1

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    Language:English  

  3. Analysis of Discrete Modern Hopfield Networks in Open Quantum System

    Takeshi Kimura, Kohtaro Kato

    arXiv e-print     2024.11

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    Authorship:Last author  

  4. Exact renormalization group flow for matrix product density operators

    Kohtaro Kato

    arXiv e-print     2024.10

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    Authorship:Lead author   Language:English  

  5. Generic increase of observational entropy in isolated systems

    Nagasawa T., Kato K., Wakakuwa E., Buscemi F.

    Physical Review Research   Vol. 6 ( 4 )   2024.10

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    Publisher:Physical Review Research  

    Observational entropy - a quantity that unifies Boltzmann's entropy, Gibbs' entropy, von Neumann's macroscopic entropy, and the diagonal entropy - was recently argued to play a key role in a modern formulation of statistical mechanics. Here, relying on algebraic techniques taken from Petz's theory of statistical sufficiency and on a Lévy-type concentration bound, we prove rigorous theorems showing how the observational entropy of a system undergoing a unitary evolution chosen at random tends to increase with overwhelming probability and to reach its maximum very quickly. More precisely, we show that for any observation that is sufficiently coarse with respect to the size of the system, regardless of the initial state of the system (be it pure or mixed), random evolution renders its state practically indistinguishable from the uniform (i.e., maximally mixed) distribution with a probability approaching 1 as the size of the system grows. The same conclusion holds not only for random evolutions sampled according to the unitarily invariant Haar distribution but also for approximate 2-designs, which are thought to provide a more physically and computationally reasonable model of random evolutions.

    DOI: 10.1103/PhysRevResearch.6.043327

    Scopus

  6. Exact and local compression of quantum bipartite states

    Kohtaro Kato

    arXiv e-print     2023.9

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    Authorship:Lead author   Language:English  

  7. Modular commutator in gapped quantum many-body systems

    Kim Isaac H., Shi Bowen, Kato Kohtaro, Albert Victor V.

    PHYSICAL REVIEW B   Vol. 106 ( 7 )   2022.8

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    Language:Japanese   Publisher:Physical Review B  

    In Phys. Rev. Lett. 128, 176402 (2022)0031-900710.1103/PhysRevLett.128.176402, we argued that the chiral central charge - a topologically protected quantity characterizing the edge theory of a gapped (2+1)-dimensional system - can be extracted from the bulk by using an order parameter called the modular commutator. In this paper, we reveal general properties of the modular commutator and strengthen its relationship with the chiral central charge. First, we identify connections between the modular commutator and conditional mutual information, time reversal, and modular flow. Second, we prove, within the framework of the entanglement bootstrap program, that two topologically ordered media connected by a gapped domain wall must have the same modular commutator in their respective bulk. Third, we numerically calculate the value of the modular commutator for a bosonic lattice Laughlin state for finite sizes and extrapolate to the infinite-volume limit. The result of this extrapolation is consistent with the proposed formula up to an error of about 0.7%.

    DOI: 10.1103/PhysRevB.106.075147

    Web of Science

    Scopus

  8. Chiral Central Charge from a Single Bulk Wave Function

    Kim Isaac H., Shi Bowen, Kato Kohtaro, Albert Victor V.

    PHYSICAL REVIEW LETTERS   Vol. 128 ( 17 ) page: 176402   2022.4

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    Language:Japanese   Publisher:Physical Review Letters  

    A (2+1)-dimensional gapped quantum many-body system can have a topologically protected energy current at its edge. The magnitude of this current is determined entirely by the temperature and the chiral central charge, a quantity associated with the effective field theory of the edge. We derive a formula for the chiral central charge that, akin to the topological entanglement entropy, is completely determined by the many-body ground state wave function in the bulk. According to our formula, nonzero chiral central charge gives rise to a topological obstruction that prevents the ground state wave function from being real valued in any local product basis.

    DOI: 10.1103/PhysRevLett.128.176402

    Web of Science

    Scopus

    PubMed

  9. Symmetry-protected sign problem and magic in quantum phases of matter

    Ellison Tyler D., Kato Kohtaro, Liu Zi-Wen, Hsieh Timothy H.

    QUANTUM   Vol. 5   2021.12

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    Language:Japanese   Publisher:Quantum  

    We introduce the concepts of a symmetry-protected sign problem and symmetry-protected magic to study the complexity of symmetry-protected topological (SPT) phases of matter. In particular, we say a state has a symmetry-protected sign problem or symmetry-protected magic, if finite-depth quantum circuits composed of symmetric gates are unable to transform the state into a non-negative real wave function or stabilizer state, respectively. We prove that states belonging to certain SPT phases have these properties, as a result of their anomalous symmetry action at a boundary. For example, we find that one-dimensional Z2 × Z2 SPT states (e.g. cluster state) have a symmetry-protected sign problem, and two-dimensional Z2 SPT states (e.g. Levin-Gu state) have symmetry-protected magic. Furthermore, we comment on the relation between a symmetry-protected sign problem and the computational wire property of one-dimensional SPT states. In an appendix, we also introduce explicit decorated domain wall models of SPT phases, which may be of independent interest.

    DOI: 10.22331/q-2021-12-28-612

    Web of Science

    Scopus

  10. Asymptotic reversibility of thermal operations for interacting quantum spin systems via generalized quantum Stein's lemma

    Sagawa Takahiro, Faist Philippe, Kato Kohtaro, Matsumoto Keiji, Nagaoka Hiroshi, Brandao Fernando G. S. L.

    JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL   Vol. 54 ( 49 )   2021.12

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    Language:Japanese   Publisher:Journal of Physics A: Mathematical and Theoretical  

    For quantum spin systems in any spatial dimension with a local, translation-invariant Hamiltonian, we prove that asymptotic state convertibility from a quantum state to another one by a thermodynamically feasible class of quantum dynamics, called thermal operations, is completely characterized by the Kullback-Leibler (KL) divergence rate, if the state is translation-invariant and spatially ergodic. Our proof consists of two parts and is phrased in terms of a branch of the quantum information theory called the resource theory. First, we prove that any states, for which the min and max Rényi divergences collapse approximately to a single value, can be approximately reversibly converted into one another by thermal operations with the aid of a small source of quantum coherence. Second, we prove that these divergences collapse asymptotically to the KL divergence rate for any translation-invariant ergodic state. We show this via a generalization of the quantum Stein's lemma for quantum hypothesis testing beyond independent and identically distributed situations. Our result implies that the KL divergence rate serves as a thermodynamic potential that provides a complete characterization of thermodynamic convertibility of ergodic states of quantum many-body systems in the thermodynamic limit, including out-of-equilibrium and fully quantum situations.

    DOI: 10.1088/1751-8121/ac333c

    Web of Science

    Scopus

  11. Matrix Product Density Operators: when do they have a local parent Hamiltonian? Invited

    Chi-Fang Chen, Kohtaro Kato, Fernando G.S.L. Brandão

    arXiv e-preprint     2020.10

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    Language:English  

  12. Toy model of boundary states with spurious topological entanglement entropy Reviewed International coauthorship

    Kohtaro Kato and Fernando G. S. L. Brandão

    PHYSICAL REVIEW RESEARCH   Vol. 2 ( 3 )   2020.7

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    Authorship:Lead author   Language:English  

    DOI: 10.1103/PhysRevResearch.2.032005

  13. Deformations of the Boundary Theory of the Square Lattice AKLT Model Reviewed

    John Martyn, Kohtaro Kato, and Angelo Lucia

    PHYSICAL REVIEW B   Vol. 102 ( 3 )   2020.6

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    Language:English  

    DOI: 10.1103/PhysRevB.102.035121

  14. Clustering of conditional mutual information for quantum Gibbs states above a threshold temperature Reviewed International coauthorship

    Tomotaka Kuwahara, Kohtaro Kato, and Fernando G. S. L. Brandão

    PHYSICAL REVIEW LETTERS   Vol. 124 ( 22 )   2020.6

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    Language:English  

    DOI: 10.1103/PhysRevLett.124.220601

  15. Fusion rules from entanglement Reviewed

    Bowen Shi, Kohtaro Kato, Isaac H. Kim

    Annals of Physics   Vol. 418   2020.6

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    Language:English  

    DOI: 10.1016/j.aop.2020.168164

  16. An entropic invariant for 2D gapped quantum phases Reviewed International coauthorship

    Kohtaro Kato, Pieter Naaijkens

    Journal of Physics A: Mathematical and Theoretical   Vol. 53 ( 8 ) page: 085302   2020.1

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    Authorship:Lead author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1088/1751-8121/ab63a5

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MISC 1

  1. トポロジカル量子計算とマヨラナ粒子 Invited

    数理科学4月号 マヨラナ粒子をめぐって   Vol. 60 ( 4 ) page: 58 - 64   2022.4

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    Language:Japanese   Publishing type:Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)  

Presentations 13

  1. Exact renormalization flow for matrix product density operators International conference

    Kato Kohtaro

    28th Quantum Information Processing Conference (QIP2025)  2025.2.25 

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    Event date: 2025.2

    Language:English   Presentation type:Poster presentation  

    Country:United States  

  2. Generalized cluster expansion: an attempt to prove locality of effective Hamiltonians Invited International conference

    Kato Kohtaro

    Correlations of quantum many-body systems  2024.12.18 

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    Event date: 2024.12

    Language:English   Presentation type:Oral presentation (invited, special)  

    Country:Germany  

  3. Exact and Local Compression of Quantum Bipartite States International conference

    Kato Kohtaro

    Quantum Extreme Universe: Matter, Information, and Gravity  2024.10.21 

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    Event date: 2024.10

    Language:English   Presentation type:Poster presentation  

    Country:Japan  

  4. Non-abelian anyons in quantum information Invited

    Kato Kohtaro

    2024.9.26 

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    Event date: 2024.9

    Language:English   Presentation type:Oral presentation (invited, special)  

    Country:Japan  

  5. Exact renormalization flow for matrix product density operators Invited International conference

    Kato Kohtaro

    Shenzhen-Nagoya Workshop on Quantum Science 2024  2024.9.21 

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    Event date: 2024.9

    Language:English   Presentation type:Oral presentation (invited, special)  

    Country:Japan  

  6. Exact and Local Compression of Quantum Bipartite States International conference

    Kato Kohtaro

    24th AQIS Conference  2024.8.27 

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    Event date: 2024.8

    Language:English   Presentation type:Poster presentation  

    Country:Japan  

  7. 非可換エニオンとトポロジカル 量子計算 Invited

    Kato Kohtaro

    創発量子現象のフロンティア: 超伝導接合、エッジ伝導、エニオン  2024.5.30 

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    Event date: 2024.5

    Language:English   Presentation type:Oral presentation (invited, special)  

    Venue:基礎物理学研究所 湯川記念館 パナソニック国際交流ホール   Country:Japan  

  8. 量子スピン系における量子情報理論的アプローチ Invited

    加藤晃太郎

    第67回物性夏の学校  2022.8.2 

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    Event date: 2022.8

    Presentation type:Public lecture, seminar, tutorial, course, or other speech  

    Venue:オンライン  

  9. Fusion rules of anyons from entanglement Invited International coauthorship

    Kohtaro Kato

    2021.11.18 

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    Event date: 2021.11

    Language:English   Presentation type:Oral presentation (invited, special)  

  10. Etanglement bootstrap approach in 2D gapped spin systems Invited International coauthorship International conference

    Kohtaro Kato

    BIRS Workshop "Topology and Entanglement in Many-Body Systems"  2021.10.13 

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    Event date: 2021.10

    Presentation type:Oral presentation (invited, special)  

  11. 非可換エニオンを用いたトポロジカル量子計算入門 Invited

    加藤晃太郎

    日本物理学会  2021.9.20 

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    Event date: 2021.9

    Language:Japanese   Presentation type:Public lecture, seminar, tutorial, course, or other speech  

    Venue:オンライン  

  12. 量子情報と量子スピン系の物理 Invited

    加藤晃太郎

    量子情報春の学校2021  2021.3.27 

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    Event date: 2021.3

    Language:Japanese   Presentation type:Public lecture, seminar, tutorial, course, or other speech  

  13. スピン系におけるトポロジカル秩序相と量子情報 Invited

    加藤晃太郎

    オンラインCRESTチュートリアル・ワークショップ「物質のトポロジカル相の理論的探究」 

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    Event date: 2021.2

    Presentation type:Public lecture, seminar, tutorial, course, or other speech  

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KAKENHI (Grants-in-Aid for Scientific Research) 5

  1. トポロジカル量子計算機アーキテクチャの理論的研究

    Grant number:24H00829  2024.4 - 2027.3

    学術変革領域研究(B)

    加藤晃太郎

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\23920000 ( Direct Cost: \18400000 、 Indirect Cost:\5520000 )

  2. 「エニオンの動的制御による情報技術の開拓」領域の総括

    Grant number:24H00826  2024.4 - 2027.3

    学術変革領域研究(B)

    橋坂 昌幸,吉岡 克将,加藤晃太郎

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    Authorship:Coinvestigator(s)  Grant type:Competitive

    Grant amount:\14430000 ( Direct Cost: \11100000 、 Indirect Cost:\3330000 )

  3. 超伝導接合系におけるエニオン: マヨラナフェルミオンを超えて

    Grant number:23K17668  2023.6 - 2026.3

    挑戦的研究(萌芽)

    田仲 由喜夫,加藤 晃太郎,星野 晋太郎

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    Authorship:Coinvestigator(s)  Grant type:Competitive

    Grant amount:\6240000 ( Direct Cost: \4800000 、 Indirect Cost:\1440000 )

  4. ギャップのある局所ハミルトニアン系に現れる多体相関の量子情報的解析

    Grant number:22K13972  2022 - 2024

    文部科学省  科学研究費助成事業  若手研究

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    Authorship:Principal investigator  Grant type:Competitive

    Direct Cost: \1900000 、 Indirect Cost:\570000 )

  5. 量子情報理論的手法による1次元テンソルネットワークの数理的解析

    Grant number:22H05254  2022 - 2023

    文部科学省  科学研究費助成事業  学術変革領域研究(A)

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    Authorship:Principal investigator  Grant type:Competitive

    Direct Cost: \900000 、 Indirect Cost:\270000 )

 

Academic Activities 1

  1. YITP international workshop "Quantum Information Entropy in Physics" International contribution

    Role(s):Planning, management, etc., Panel moderator, session chair, etc.

    加藤晃太郎 (Chair)   2022.3

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    Type:Academic society, research group, etc.