Updated on 2025/04/27

Information

 

写真a

 
YAMAGUCHI KOJI
 
Organization
Faculty of Information Science and Electrical Engineering Department of Informatics Academic Researcher
Title
Academic Researcher

Research Areas

  • Natural Science / Mathematical physics and fundamental theory of condensed matter physics

Research History

  • Kyushu University Faculty of Information Science and Electrical Engineering Department of Informatics Academic Researcher 特任助教

    2025.4 - Present

  • The University of Electro-Communications Graduate School of Informatics and Engineering 特任研究員・日本学術振興会特別研究員(PD) 

    2024.4 - 2025.3

  • The University of Electro-Communications Graduate School of Informatics and Engineering 特任研究員 

    2023.10 - 2024.3

  • University of Waterloo Department of Applied Mathematics JSPS Overseas Research Fellow 

    2021.10 - 2023.9

  • The University of Electro-Communications Graduate School of Informatics and Engineering 特任研究員 

    2021.4 - 2021.9

  • Japan Society for the Promotion of Science  特別研究員(DC1) 

    2018.4 - 2021.3

  • Tohoku University Graduate School of Science Department of Physics Research assistant 

    2017.4 - 2021.3

▼display all

Education

  • Tohoku University   Graduate School of Science   Department of Physics

    2018.4 - 2021.3

  • Tohoku University   Graduate School of Science   Department of Physics

    2016.4 - 2018.3

  • Kyoto University   Faculty of Science   Faculty of Science

    2012.4 - 2016.3

Research Interests・Research Keywords

  • Research theme: 量子情報

    Keyword: 量子情報

    Research period: 2025

  • Research theme: リソース理論

    Keyword: リソース理論

    Research period: 2025

  • Research theme: 情報スペクトル

    Keyword: 情報スペクトル

    Research period: 2025

  • Research theme: 相対論的量子情報

    Keyword: 相対論的量子情報

    Research period: 2025

  • Research theme: ブラックホール

    Keyword: ブラックホール

    Research period: 2025

Awards

  • 物理学専攻賞(博士)

    2021.3   東北大学  

  • 物理学専攻賞(修士)

    2017.3   東北大学  

Papers

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

    Koji Yamaguchi, Hiroyasu Tajima

    Physical Review Letters   131 ( 20 )   2023.11

     More details

    Authorship:Lead author, Corresponding author   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevLett.131.200203

  • Entanglement partners and monogamy in de Sitter universes Reviewed

    Yasusada Nambu, Koji Yamaguchi

    Physical Review D   108 ( 4 )   2023.8

     More details

    Authorship:Last author   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevD.108.045002

  • Entanglement is better teleported than transmitted Reviewed

    Koji Yamaguchi, Achim Kempf

    Physical Review D   108 ( 2 )   2023.7

     More details

    Authorship:Lead author, Corresponding author   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevD.108.025004

  • Smooth Metric Adjusted Skew Information Rates Reviewed

    Koji Yamaguchi, Hiroyasu Tajima

    Quantum   7   1012   2023.5

     More details

    Authorship:Lead author, Corresponding author   Publishing type:Research paper (scientific journal)  

    DOI: 10.22331/q-2023-05-22-1012

  • Modification of a Lie-algebra-based approach and its application to asymptotic symmetries on a Killing horizon Reviewed

    Takeshi Tomitsuka, Koji Yamaguchi

    Progress of Theoretical and Experimental Physics   2022 ( 4 )   2022.3   ISSN:2050-3911 eISSN:2050-3911

     More details

    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Oxford University Press (OUP)  

    Abstract

    We develop a new approach to find asymptotic symmetries in general relativity as a modification of the Lie-algebra-based approach proposed in T. Tomitsuka et al. [Classical Quantum Gravity 38, 225007 (2021)]. Those authors proposed an algorithmic protocol to investigate asymptotic symmetries. In particular, their guiding principle helps us to find a non-vanishing charge that generates an infinitesimal diffeomorphism. However, in order to check the integrability condition for the charges, it is necessary to solve differential equations to identify the integral curve of vector fields, which is usually quite hard. In this paper, we provide a sufficient condition of the integrability condition that can be checked without solving any differential equations, avoiding the difficulties in the approach in the above reference. As a demonstration, we investigate the asymptotic symmetries on a Killing horizon and find a new class of asymptotic symmetries. In 4D spacetimes with a spherical Killing horizon, we show that the algebra of the corresponding charges is a central extension of the algebra of vector fields.

    DOI: 10.1093/ptep/ptac046

    Other Link: https://academic.oup.com/ptep/article-pdf/2022/4/043E02/43296791/ptac046.pdf

  • A Lie algebra based approach to asymptotic symmetries in general relativity Reviewed

    Takeshi Tomitsuka, Koji Yamaguchi, Masahiro Hotta

    Classical and Quantum Gravity   38 ( 22 )   225007 - 225007   2021.10   ISSN:0264-9381 eISSN:1361-6382

     More details

    Publishing type:Research paper (scientific journal)   Publisher:IOP Publishing  

    DOI: 10.1088/1361-6382/ac2c1e

    Other Link: https://iopscience.iop.org/article/10.1088/1361-6382/ac2c1e/pdf

  • Superadditivity of channel capacity through quantum fields Reviewed

    Koji Yamaguchi, Aida Ahmadzadegan, Petar Simidzija, Achim Kempf, Eduardo Martín-Martínez

    Physical Review D   101 ( 10 )   2020.5   ISSN:2470-0029

     More details

    Authorship:Lead author, Corresponding author   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevD.101.105009

    Scopus

  • Information Stored in Correlations and Quantum Information Capsule Invited Reviewed

    Koji Yamaguchi, Masahiro Hotta

    日本物理学会誌   75 ( 5 )   284 - 288   2020.5

     More details

    Authorship:Lead author, Corresponding author  

    DOI: 10.11316/butsuri.75.5_284

  • Strong chaos of fast scrambling yields order: Emergence of decoupled quantum information capsules Reviewed

    Hotta, M., Yamaguchi, K.

    Physics Letters, Section A: General, Atomic and Solid State Physics   384 ( 3 )   126078 - 126078   2020   ISSN:0375-9601

     More details

    Authorship:Last author   Publishing type:Research paper (scientific journal)   Publisher:Elsevier {BV}  

    DOI: 10.1016/j.physleta.2019.126078

    Scopus

  • A fundamental upper bound for signal to noise ratio of quantum detectors Reviewed

    Katsube, R., Hotta, M., Yamaguchi, K.

    Journal of the Physical Society of Japan   89 ( 5 )   2020   ISSN:1347-4073

     More details

    Publishing type:Research paper (scientific journal)  

    DOI: 10.7566/JPSJ.89.054005

    Scopus

  • Duality in the dynamics of Unruh-DeWitt detectors in conformally related spacetimes Reviewed

    Hotta, M., Kempf, A., Mart{\'i}n-Mart{\'i}nez, E., Tomitsuka, T., Yamaguchi, K.

    Physical Review D   101 ( 8 )   2020   ISSN:2470-0029

     More details

    Authorship:Last author   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevD.101.085017

    Scopus

  • Partner formula for an arbitrary moving mirror in 1+1 dimensions Reviewed

    Tomitsuka, T., Yamaguchi, K., Hotta, M.

    Physical Review D   101 ( 2 )   2020   ISSN:2470-0029

     More details

    Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevD.101.024003

    Scopus

  • Quantum information capsule in multiple-qudit systems and continuous-variable systems Reviewed

    Yamaguchi, K., Hotta, M.

    Physics Letters, Section A: General, Atomic and Solid State Physics   384 ( 23 )   2020   ISSN:0375-9601

     More details

    Authorship:Lead author, Corresponding author   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.physleta.2020.126447

    Scopus

  • Theorems on Entanglement Typicality in Non-equilibrium Dynamics Reviewed

    Koji Yamaguchi

    Journal of the Physical Society of Japan   88 ( 6 )   2019.6   ISSN:1347-4073

     More details

    Authorship:Lead author, Last author, Corresponding author   Publishing type:Research paper (scientific journal)  

    DOI: 10.7566/JPSJ.88.064002

    Scopus

  • Quantum information capsule and information delocalization by entanglement in multiple-qubit systems Reviewed

    Koji Yamaguchi, Naoki Watamura, Masahiro Hotta

    Physics Letters A   383 ( 12 )   1255 - 1259   2019.4   ISSN:03759601

     More details

    Authorship:Lead author, Corresponding author   Publishing type:Research paper (scientific journal)   Publisher:Elsevier {BV}  

    DOI: 10.1016/j.physleta.2019.01.036

  • Spatially overlapped partners in quantum field theory Reviewed

    Jose Trevison, Koji Yamaguchi, Masahiro Hotta

    Journal of Physics A: Mathematical and Theoretical   52 ( 12 )   2019   ISSN:1751-8121

     More details

    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Institute of Physics Publishing  

    In quantum field theory particles are physically defined as what Unruh-De Witt particle detectors observe. By detecting a particle mode A, a reduced density operator for a quantum state of A is constructed. Even if the entire quantum state of the quantum field is pure, the state of A is not pure but mixed due to entanglement between other subsystems. The partner mode B of the field is defined as a purification partner of A such that the AB system in a pure state. We show that, without any fine-tuning of the particle detector design of A, the weighting function of partner B has spatial overlap of that of A. We show a general formula of partner B associated with arbitrarily fixed A of a free field in a general Gaussian state. We demonstrate an example of memory effects in an expanding Freedman-Robertson-Walker universe.

    DOI: 10.1088/1751-8121/ab065b

    Scopus

  • Pure state entanglement harvesting in quantum field theory Reviewed

    Jose Trevison, Koji Yamaguchi, Masahiro Hotta

    Progress of Theoretical and Experimental Physics   2018 ( 10 )   2018.10   ISSN:2050-3911

     More details

    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Physical Society of Japan  

    Quantum fields in vacuum states carry an infinite amount of quantum entanglement, and its entanglement entropy has ultraviolet divergence. Harvesting protocols of the vacuum entanglement have been investigated, but its efficiency is very low to date. The main reason for the low efficiency originates from the fact that the extracted entanglement is embedded in a mixed state of two external devices. We propose a general protocol with high efficiency by extracting pure state entanglement from the field. We only use bi-linear interactions between the fields and external devices. Even though the ultraviolet cutoff remains finite, the protocol is capable of extracting a huge amount of entanglement. Hence an infinite amount of entanglement extraction is attained without the ultraviolet divergence of the field entanglement entropy in a continuum limit. There exists a trade-off relation between the extracted entanglement and its energy cost.

    DOI: 10.1093/ptep/pty109

    Scopus

  • Soft-Hair-Enhanced Entanglement beyond Page Curves in a Black Hole Evaporation Qubit Model Reviewed

    Masahiro Hotta, Yasusada Nambu, Koji Yamaguchi

    Physical Review Letters   120 ( 18 )   2018.5   ISSN:1079-7114

     More details

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

    We propose a model with multiple qubits that reproduces the thermal properties of four-dimensional Schwarzschild black holes (BHs) by simultaneously taking account of the emission of Hawking particles and the zero-energy soft-hair evaporation at the horizon. The results verify that the entanglement entropy between a qubit and other subsystems, including emitted radiation, is much larger than the BH entropy analogue of the qubit, as opposed to the Page curve prediction. Our result suggests that early Hawking radiation is entangled with soft hair and that late Hawking radiation can be highly entangled with the degrees of freedom of a BH, avoiding the emergence of a firewall at the horizon.

    DOI: 10.1103/PhysRevLett.120.181301

    Scopus

    PubMed

  • Gravitational memory charges of supertranslation and superrotation on Rindler horizons Reviewed

    Masahiro Hotta, Jose Trevison, Koji Yamaguchi

    PHYSICAL REVIEW D   94 ( 8 )   2016.10   ISSN:2470-0010 eISSN:2470-0029

     More details

    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    In a Rindler-type coordinate system spanned in a region outside of a black hole horizon, we have nonvanishing classical holographic charges as soft hairs on the horizon for stationary black holes. Taking a large black hole mass limit, the spacetimes with the charges are described by asymptotic Rindler metrics. We construct a general theory of gravitational holographic charges for a (1 + 3)-dimensional linearized gravity field in the Minkowski background with Rindler horizons. Although matter crossing a Rindler horizon causes horizon deformation and a time-dependent coordinate shift-that is, gravitational memory-the supertranslation and superrotation charges on the horizon can be defined during and after its passage through the horizon. It is generally proven that holographic states on the horizon cannot store any information about absorbed perturbative gravitational waves. However, matter crossing the horizon really excites holographic states. By using gravitational memory operators, which consist of the holographic charge operators, we suggest a resolution of the no-cloning paradox of quantum information between matter falling into the horizon and holographic charges on the horizon from the viewpoint of the contextuality of quantum measurement.

    DOI: 10.1103/PhysRevD.94.083001

    Web of Science

▼display all

Presentations

  • Quantum geometric tensor determines the i.i.d. conversion rate in the resource theory of asymmetry for any compact Lie group

    Koji Yamaguchi

    28th Quantum Information Processing Conference (QIP 2025)  2025.2 

     More details

    Event date: 2025.2

    Language:English   Presentation type:Oral presentation (general)  

  • Quantum information capsule and its application to information transmission

    Koji Yamaguchi

    Relativistic Quantum Information 13 Workshop (South) 

     More details

    Event date: 2019.2

    Language:English   Presentation type:Oral presentation (general)  

  • Building block approach to asymptotic symmetries in general relativity

    Koji Yamaguchi

    RQI-Online 2020/21  2021.2 

     More details

    Language:English   Presentation type:Oral presentation (general)  

  • Partners and quantum information capsule

    Koji Yamaguchi

    Future Perspective in Cosmology and Gravity  2019.4 

     More details

    Language:English   Presentation type:Oral presentation (general)  

  • Partners and Quantum Information Capsule

    Koji Yamaguchi

    Relativistic Quantum Information- North 2019  2019.5 

     More details

    Language:English   Presentation type:Oral presentation (general)  

  • Quantum Information Capsule and Information Delocalization by Entanglement in Multiple-qubit Systems

    山口幸司

    日本物理学会第74回年次大会  2019.3 

     More details

    Presentation type:Oral presentation (general)  

  • Quantum Information Capsule and Information Delocalization by Entanglement in Multiple-qubit Systems

    Koji Yamaguchi

    Quantum Information and String Theory 2019  2019.6 

     More details

    Language:English   Presentation type:Poster presentation  

  • Theorems on Entanglement Typicality in Non-equilibrium Dynamics

    Koji Yamaguchi

    日本物理学会2018年秋季大会  2018.9 

     More details

    Language:Japanese   Presentation type:Oral presentation (general)  

  • Theorems on Entanglement Typicality in Non-equilibrium Dynamics

    Koji Yamaguchi

    Relativistic Quantum Information-North 2018  2018.9 

     More details

    Language:English   Presentation type:Poster presentation  

  • Theorems on Entanglement Typicality in Non-equilibrium Dynamics

    山口幸司

    量子情報・物性の新潮流  2018.8 

     More details

    Language:Japanese   Presentation type:Poster presentation  

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

    Koji Yamaguchi

    Beyond IID in Information Theory 10  2022.9 

     More details

    Language:English   Presentation type:Oral presentation (general)  

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

    Koji Yamaguchi

    Quantum resources: from mathematical foundations to operational characterisation  2022.12 

     More details

    Language:English   Presentation type:Oral presentation (general)  

  • Entanglement is better teleported than transmitted

    Koji Yamaguchi

    Relativistic Quantum Information-North 2022  2022.9 

     More details

    Language:English   Presentation type:Oral presentation (general)  

  • Improving the efficiently of transmitting quantum information by utilizing correlated quantum fluctuations

    Koji Yamaguchi

    13th Annual Conference on Relativistic Quantum Information (North)  2023.7 

     More details

    Language:English   Presentation type:Oral presentation (general)  

  • Quantum geometric tensor determines the i.i.d. conversion rate in the resource theory of asymmetry for any compact Lie group

    Koji Yamaguchi

    Quantum Resources 2025  2025.3 

     More details

    Language:English   Presentation type:Poster presentation  

  • コンパクトLie群についての非対称性リソース理論におけるi.i.d.状態変換レートの量子幾何テンソルによる決定

    山口幸司

    日本物理学会 2025年春季大会  2025.3 

     More details

    Language:Japanese   Presentation type:Oral presentation (general)  

  • 量子フィッシャー情報量の情報スペクトル的拡張によるエネルギーコヒーレンスの漸近変換の一般論

    山口幸司

    日本物理学会2024年春季大会  2024.3 

     More details

    Language:Japanese   Presentation type:Oral presentation (general)  

  • 非対称性のリソース理論におけるsmooth metric adjusted skew informationとその漸近レート

    山口幸司

    日本物理学会 第79回年次大会  2024.9 

     More details

    Language:Japanese   Presentation type:Oral presentation (general)  

▼display all

MISC

  • Encrypted Qubits can be Cloned

    Koji Yamaguchi, Achim Kempf

    2025.1

     More details

    We show that encrypted cloning of unknown quantum states is possible. Any
    number of encrypted clones of a qubit can be created through a unitary
    transformation, and each of the encrypted clones can be decrypted through a
    unitary transformation. The decryption of an encrypted clone consumes the
    decryption key, i.e., only one decryption is possible, in agreement with the
    no-cloning theorem. A possible application of encrypted cloning is to enable
    encrypted quantum multi-cloud storage. Beyond applications in cryptography,
    encrypted cloning could provide a form of redundancy, parallelism, fault
    tolerance or scalability where direct duplication is forbidden by the
    no-cloning theorem.

    arXiv

    Other Link: http://arxiv.org/pdf/2501.02757v1

  • Quantum geometric tensor determines the i.i.d. conversion rate in the resource theory of asymmetry for any compact Lie group

    Koji Yamaguchi, Yosuke Mitsuhashi, Tomohiro Shitara, Hiroyasu Tajima

    2024.11

     More details

    Symmetry is one of the most significant foundational principles underlying
    nature. The resource theory of asymmetry (RTA) is a resource-theoretic
    framework for investigating asymmetry as a resource to break constraints
    imposed by symmetries. It has recently undergone significant developments,
    resulting in applications in a variety of research areas since symmetry and its
    breaking are ubiquitous in physics. Nevertheless, the resource conversion
    theory at the core of RTA remains incomplete. In the independent and
    identically distributed (i.i.d.) setup, where identical copies of a state are
    converted to identical copies of another state, conversion theory among pure
    states has been completed only for $U(1)$ group and finite groups. Here, we
    establish an i.i.d. conversion theory among any pure states in RTA for any
    continuous symmetry described by a compact Lie group, which includes the cases
    where multiple conserved quantities are involved. We show that the quantum
    geometric tensor is an asymmetry monotone for pure states that determines the
    optimal approximate asymptotic conversion rate. Our formulation achieves a
    unified understanding of conversion rates in prior studies for different
    symmetries. As a corollary of the formula, we also affirmatively prove the
    Marvian-Spekkens conjecture on reversible asymptotic convertibility in RTA,
    which has remained unproven for a decade.

    arXiv

    Other Link: http://arxiv.org/pdf/2411.04766v2

Media Coverage

  • Quanten-Dolly | Schlupfloch in einem Quantengesetz

    Spektrum der Wissenschaft  https://www.spektrum.de/news/qubits-koennen-geklont-werden-wenn-man-sie-verschluesselt/2260066  2025.4