KEIO RESEARCHERS INFORMATION SYSTEM

Career 【 Display / hide 】

Career 【 Display / hide 】

• 2007.04

  -

  2009.08

  RIKEN, Condensed Matter Theory Laboratory, Special Postdoctoral Researcher

• 2009.09

  -

  2011.06

  University of Toronto, Department of Physics, Postdoctoral Fellow

• 2011.07

  -

  2012.08

  University of Tokyo, Department of Physics, Postdoctoral Researcher

• 2012.08

  -

  2019.03

  University of Tokyo, Department of Physics, Assistant Professor

• 2019.04

  -

  2025.03

  Keio University, Department of Physics, Assistant Professor

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Academic Background 【 Display / hide 】

Academic Background 【 Display / hide 】

• 1999.04

  -

  2002.03

  Tokyo Institute of Technology, School of Science, Department of Physics

  University, Skipped grade(s)

• 2002.04

  -

  2004.03

  Tokyo Institute of Technology, Graduate School of Science, Department of Physics

  Graduate School, Completed, Master's course

• 2004.04

  -

  2007.03

  Tokyo Institute of Technology, Graduate School of Science, Department of Physics

  Graduate School, Completed, Doctoral course

Academic Degrees 【 Display / hide 】

Academic Degrees 【 Display / hide 】

• 博士（理学）, Tokyo Institute of Technology, Coursework, 2007.03

  Characterization of Exotic Orders in Quantum Spin Systems

Research Areas 【 Display / hide 】

Research Areas 【 Display / hide 】

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

• Natural Science / Semiconductors, optical properties of condensed matter and atomic physics

Research Keywords 【 Display / hide 】

Research Keywords 【 Display / hide 】

• topological states of matter

• ultracold atomic systems

• magnetism

Research Themes 【 Display / hide 】

Research Themes 【 Display / hide 】

• Competition of topological and ordered phases in spin ladder systems, 

  2022.07

  -

  Present

• Vortex lattices in Bose-Einstein condensates in synthetic gauge fields, 

  2017.01

  -

  2022.05

• Quantum critical phenomena in non-Hermitian quantum many-body systems, 

  2015.12

  -

  Present

• Theory of frustrated magnetism of volborthite based on a coupled-trimer model, 

  2015.03

  -

  Present

• Quantum Hall physics of ultracold atomic systems in synthetic gauge fields, 

  2011.07

  -

  Present

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Papers 【 Display / hide 】

Papers 【 Display / hide 】

• High-Field Magnetism of the Spin-1/2 Two-Leg-Ladder Antiferromagnet Cu(DEP)Cl2 under High Pressure

  Morimoto T., Morikawa E., Nihongi K., Kida T., Narumi Y., Honda Z., Furukawa S., Uwatoko Y., Kindo K., Hagiwara M.

  Journal of the Physical Society of Japan 94 ( 2 )  2025.02

  ISSN  00319015

  　View Summary

  We report the magnetic properties of powder samples of the two-leg-ladder antiferromagnet Cu(DEP)Cl2 (DEP: 2,3-diethylpyradine) measured in magnetic fields of up to 40 T under pressures (P) of up to 1.7 GPa. Measured magnetic properties (magnetic susceptibility and high-field magnetization with two transition fields) at ambient P are compared with those calculated by a quantum Monte Carlo method and are well explained by the two-leg-ladder antiferromagnetic model with large rung exchange interaction (Jrung). A peak of magnetic susceptibility shifts largely to a higher temperature with a significant decrease in height, and both transition fields shift largely to higher fields at a critical pressure Pc of approximately 0.2 GPa. The results of an evaluation of these exchange constants below and above Pc indicate that antiferromagnetic two-leg ladders (Jrung > Jleg) with a very weak Jint changed into strongly coupled (Jrung) antiferromagnetic dimers with weak Jleg and Jint

  • Access to Document (DOI)

• Phase Diagram of a Spin-\(\frac{1}{2}\) Heisenberg Ladder with a Chirality–Chirality Interaction

  Fontaine M., Furukawa S.

  Journal of the Physical Society of Japan 93 ( 12 )  2024.12

  ISSN  00319015

  　View Summary

  A spin-12 Heisenberg model with a chirality–chirality interaction (CCI) on a two-leg ladder provides a minimal setup to explore an interplay between spin and chirality degrees of freedom. This model is potentially relevant for understanding the effects of a four-spin ring exchange and a phonon-mediated interaction on a ladder. By applying the Abelian bosonization and two types of spin-chirality duality, we derive a comprehensive ground-state phase diagram that includes previously unexplored cases of a ferromagnetic rung exchange Jτ < 0 or a negative CCI Kch < 0. The phase diagram consists of the rung singlet (RS) phase, the Haldane phase, and three non-magnetic ordered phases. Moreover, the RS and Haldane phases consist of several regions with different dominant correlations in terms of spin, dimer, or chirality. We perform numerical simulations to confirm the predicted phase structure and critical properties.

  • Access to Document (DOI)

• System-environment entanglement phase transitions

  Ashida Y., Furukawa S., Oshikawa M.

  Physical Review B 110 ( 9 )  2024.09

  ISSN  24699950

  　View Summary

  Entanglement in quantum many-body systems can exhibit universal phenomena governed by long-distance properties. We study universality and phase transitions of the entanglement inherent to open many-body systems, namely, the entanglement between a system of interest and its environment. Specifically, we consider the Tomonaga-Luttinger liquid (TLL) under a local measurement and analyze its unconditioned nonunitary evolution, where the measurement outcomes are averaged over. We quantify the system-environment entanglement by the Rényi entropy of the post-measurement density matrix, whose size-independent term encodes the universal low-energy physics. We develop a field-theoretical description to relate the universal term to the effective ground-state degeneracy known as the g function in a boundary conformal field theory, and use the renormalization group method to determine its value. We show that the universal contribution is determined by the TLL parameter K and can exhibit singularity signifying an entanglement phase transition. Surprisingly, in certain cases the size-independent contribution can increase as a function of the measurement strength in contrast to what is naïvely expected from the g-theorem. We argue that this unconventional behavior could be attributed to the dangerously irrelevant term which has been found in studies of the resistively shunted Josephson junction. We also check these results by numerical calculations in the spin-12 XXZ chain subject to a site-resolved measurement. Possible experimental realization in ultracold gases, which requires no postselections, is discussed.

  • Access to Document (DOI)

• Symmetry, topology, duality, chirality, and criticality in a spin-1/2 XXZ ladder with a four-spin interaction

  Fontaine M., Sugimoto K., Furukawa S.

  Physical Review B (American Physical Society)  109 ( 13 ) 134413 2024.04

  Research paper (scientific journal), Joint Work, Accepted,  ISSN  24699950

  　View Summary

  We study the ground-state phase diagram of a spin-12 XXZ model with a chirality-chirality interaction (CCI) on a two-leg ladder. This model offers a minimal setup to study an interplay between spin and chirality degrees of freedom. The spin-chirality duality transformation allows us to relate the regimes of weak and strong CCIs. By applying the Abelian bosonization and the duality, we obtain a rich phase diagram that contains distinct gapped featureless and ordered phases. In particular, Néel and vector chiral orders appear for easy-axis anisotropy, while two distinct symmetry-protected topological (SPT) phases appear for easy-plane anisotropy. The two SPT phases can be viewed as twisted variants of the Haldane phase. We also present an effective description in terms of (spinor) hard-core bosons, which reveals critical behavior on the self-dual line in the easy-axis and easy-plane regimes. We perform numerical simulations to confirm the predicted phase structure and critical properties. We further demonstrate that the two SPT phases and a trivial phase are distinguished by topological indices in the presence of certain symmetries. A similar phase structure is expected in a spin-12 XXZ ladder with four-spin ring exchange.

  • Access to Document (DOI)

• Ground-state phase diagram of a spin-1/2 frustrated XXZ ladder

  Ogino T., Kaneko R., Morita S., Furukawa S.

  Physical Review B (American Physical Society)  106 ( 15 ) 155106 2022.10

  Research paper (scientific journal), Joint Work, Accepted,  ISSN  24699950

  　View Summary

  We study the ground-state phase diagram of a spin-12 frustrated XXZ ladder, in which two antiferromagnetic chains are coupled by competing rung and diagonal interactions, J⊥ and J×. Previous studies on the isotropic model have revealed that a fluctuation-induced effective dimer attraction between the legs stabilizes the columnar dimer (CD) phase in the highly frustrated regime J⊥≈2J×, especially for ferromagnetic J⊥,×<0. By means of effective field theory and numerical analyses, we extend this analysis to the XXZ model, and we obtain a rich phase diagram. The diagram includes four gapped featureless phases with no symmetry breaking: the rung singlet (RS) and Haldane phases as well as their twisted variants, the RS∗ and Haldane∗ phases, which are all distinct in the presence of certain symmetries. Significantly, the Haldane-CD transition point in the isotropic model turns out to be a crossing point of two transition lines in the XXZ model, and the stripe Néel and RS∗ phases appear between these lines. This indicates a nontrivial interplay between the effective dimer attraction and the exchange anisotropy. In the easy-plane regime, the four featureless phases and two critical phases are found to compete in a complex manner depending on the signs of J⊥,×.

  • Access to Document (DOI)

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Papers, etc., Registered in KOARA 【 Display / hide 】

Papers, etc., Registered in KOARA 【 Display / hide 】

• Theoretical study of many-body effects in Bose-Einstein condensates in synthetic gauge fields

  Furukawa, Shunsuke

  学事振興資金研究成果実績報告書 (慶應義塾大学)  2019

Reviews, Commentaries, etc. 【 Display / hide 】

Reviews, Commentaries, etc. 【 Display / hide 】

• Entanglement entropy and conformal field theory

  S. Furukawa, J. Shiraishi

  BUTSURI 69 ( 8 ) 541 - 546 2014

  Article, review, commentary, editorial, etc. (scientific journal), Joint Work

  • Access to Document (DOI)

Presentations 【 Display / hide 】

Presentations 【 Display / hide 】

• スピン梯子系におけるトポロジカルエンタングルメントスワッピング

  濱田瑞貴, 古川俊輔

  日本物理学会2025年春季大会 (オンライン) , 

  2025.03

  , 

  Oral presentation (general)

• スピン梯子系におけるトポロジカルエンタングルメントスワッピング

  濱田瑞貴, 古川俊輔

  サスティナブル量子AI研究拠点第5回全体会議 (慶應義塾大学日吉キャンパス ) , 

  2025.02

  , 

  Poster presentation

• 量子多体系における測定と場の理論

  古川俊輔

  場の理論の新しい計算方法2024 (東京大学駒場Ⅱキャンパス) , 

  2024.12

  , 

  Public lecture, seminar, tutorial, course, or other speech

• Investigation of topological phases and transitions via quantum control, quantum entanglement, and duality

  Shunsuke Furukawa

  The 4th ExU Annual Meeting of the Extreme Universe Collaboration (Nambu Yoichiro Hall, Osaka University) , 

  2024.09

  , 

  Oral presentation (general)

• Symmetry, topology, duality, chirality, and criticality in a spin-1/2 XXZ ladder with a four-spin interaction

  M. Fontaine, K. Sugimoto, S. Furukawa

  SUN2024 : SU(N) physics in quantum many-body systems: theory, experiment, and numerics (Sendai) , 

  2024.07

  , 

  Poster presentation

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Research Projects of Competitive Funds, etc. 【 Display / hide 】

Research Projects of Competitive Funds, etc. 【 Display / hide 】

• Investigation of topological phases and transitions via quantum control, quantum entanglement, and duality

  2024.04

  -

  2026.03

  Grants-in-Aid for Scientific Research, Grant-in-Aid for Transformative Research Areas (A), No Setting

  　View Summary

  液相から固相への転移が分子の自発的な秩序化として理解される一方、そのような秩序化では捉えられない奇妙な物質相としてトポロジカル相が知られ、量子磁性体や半導体などにおいて盛んに研究されている。本研究では、トポロジカル相研究の新しい舞台として、急速に技術革新の進む量子コンピュータに着目する。クラウド利用できる量子コンピュータを利用してトポロジカル状態をつくり出し、量子誤り軽減法によりノイズの影響を抑えたもとで非局所相関関数などの量子計算を行う。また、トポロジカル相に内在する量子もつれを量子情報の視点から特徴づける方法を発展させ、物性物理学と量子情報の融合領域の開拓を推進する。

• Theoretical study of many-body effects in Bose-Einstein condensates in synthetic gauge fields

  2019.04

  -

  2020.03

  Keio Gijuku, Academic Development Funds, Shunsuke Furukawa, Research grant, Principal investigator

• Symmetry-enriched topological phases: theoretical foundation and proposal for realization

  2018.04

  -

  2024.03

  MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), Principal investigator

• Phase frustration in Bose-Einstein condensates in optical lattices

  2016.11

  -

  2019.03

  Matsuo Foundation, Shunsuke Furukawa, Research grant, Principal investigator

• Exploration of topological orders in strongly correlated ultracold atomic systems and development of their fundamental theory

  2013.04

  -

  2017.03

  The University of Tokyo, FURUKAWA SHUNSUKE, Grant-in-Aid for Young Scientists (B), No Setting

  　View Summary

  Topologically ordered states exhibit a number of intriguing properties such as quantized responses and quasiparticles obeying fractional statistics. In this study, we have theoretically explored novel topologically ordered states that can be realized in highly controlled ultracold atomic systems, and investigated their physical properties. In particular, we have determined detailed ground-state phase diagrams of two-component Bose gases in synthetic gauge fields, and revealed (i) the appearance of a bosonic integer quantum Hall state with unusual edge states and (ii) a nontrivial role of time-reversal symmetry in the interaction effect. We have also shown that Bose-Einstein condensate in optical lattices can host an excitation band with nontrivial topology, and that edge states originating from it can be observed by exploiting a macroscopic quantum interference.

Awards 【 Display / hide 】

Awards 【 Display / hide 】

• The 2nd High Magnetic Field Forum Frontier Incentive Award

  Shunsuke Furukawa, 2020.12, The High Magnetic Field Forum of Japan, Theoretical studies on quantum magnets with competing ferromagnetic and antiferromagnetic interactions

  Type of Award： Award from Japanese society, conference, symposium, etc.

  　View Description

  http://www.issp.u-tokyo.ac.jp/labs/mgsl/himag-forum/frontier.html

• The 7th Young Scientist Award of the Physical Society of Japan

  Shunsuke Furukawa, 2013.03, Physical Society of Japan, Entanglement entropy in quantum many-body systems

  Type of Award： Award from Japanese society, conference, symposium, etc.

  　View Description

  https://www.jps.or.jp/activities/awards/jusyosya/wakate2013.html#r11
  http://www.r11.div.jps.or.jp/wakate07.html
  https://ss.scphys.kyoto-u.ac.jp/TQP/achievements/newsletters.html#no3

Courses Taught 【 Display / hide 】

Courses Taught 【 Display / hide 】

• THERMODYNAMICS

  2025

• STATISTICAL PHYSICS B

  2025

• PHYSICS SEMINAR 4

  2025

• PHYSICS B

  2025

• OFF-CAMPUS WORK-STUDY PROGRAM

  2025

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Memberships in Academic Societies 【 Display / hide 】

Memberships in Academic Societies 【 Display / hide 】

• Physical Society of Japan, 

  2004.01

  -

  Present

Committee Experiences 【 Display / hide 】

Committee Experiences 【 Display / hide 】

• 2022.04

  -

  2023.03

  新著紹介小委員会 委員長（兼 会誌編集委員）, 日本物理学会

• 2021.04

  -

  2022.03

  新著紹介小委員会 委員, 日本物理学会

• 2020.04

  -

  2021.03

  領域３（磁性）運営委員, 日本物理学会