古川 俊輔 (フルカワ シュンスケ)

Furukawa, Shunsuke



理工学部 物理学科 (矢上)





経歴 【 表示 / 非表示

  • 2007年04月

    理化学研究所, 物性理論研究室, 基礎科学特別研究員

  • 2009年09月

    トロント大学, 物理学科, ポストドクトラル・フェロー

  • 2011年07月

    東京大学, 大学院理学系研究科 物理学専攻, 特任研究員

  • 2012年08月

    東京大学, 大学院理学系研究科 物理学専攻, 助教

  • 2019年04月

    慶應義塾大学, 理工学部 物理学科, 専任講師

学歴 【 表示 / 非表示

  • 1999年04月

    東京工業大学, 理学部, 物理学科

    大学, 飛び級

  • 2002年04月

    東京工業大学, 理工学研究科, 物性物理学専攻

    大学院, 修了, 修士

  • 2004年04月

    東京工業大学, 理工学研究科, 物性物理学専攻

    大学院, 修了, 博士後期

学位 【 表示 / 非表示

  • 博士(理学), 東京工業大学, 課程, 2007年03月

    Characterization of Exotic Orders in Quantum Spin Systems


研究分野 【 表示 / 非表示

  • 自然科学一般 / 数理物理、物性基礎

  • 自然科学一般 / 半導体、光物性、原子物理

研究キーワード 【 表示 / 非表示

  • トポロジカル物性

  • 冷却原子系

  • 磁性

研究テーマ 【 表示 / 非表示

  • スピン梯子系におけるトポロジカル相と秩序相の競合, 


  • 人工ゲージ場中のボース・アインシュタイン凝縮体における渦格子, 


  • 非エルミート量子多体系における量子臨界現象, 


  • 結合トライマー模型に基づくボルボサイトのフラストレート磁性の理論, 


  • 人工ゲージ場中の冷却原子系における量子ホール物理, 


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論文 【 表示 / 非表示

  • Vortex lattices in binary Bose–Einstein condensates: collective modes, quantum fluctuations, and intercomponent entanglement

    Takumi Yoshino and Shunsuke Furukawa and Masahito Ueda

    Journal of Physics B: Atomic, Molecular and Optical Physics (IOP Publishing)  55 ( 10 )  2022年05月

    ISSN  0953-4075


    We study binary Bose-Einstein condensates subject to synthetic magnetic fields in mutually parallel or antiparallel directions. Within the mean-field theory, the two types of fields have been shown to give the same vortex-lattice phase diagram. We develop an improved effective field theory to study properties of collective modes and ground-state intercomponent entanglement. Here, we point out the need to introduce renormalized coupling constants for coarse-grained densities. We show that the low-energy excitation spectra for the two types of fields are related to each other by suitable rescaling with the renormalized coupling constants. By calculating the entanglement entropy, we find that for an intercomponent repulsion (attraction), the two components are more strongly entangled in the case of parallel (antiparallel) fields, in qualitative agreement with recent studies for a quantum (spin) Hall regime. We also find that the entanglement spectrum exhibits an anomalous square-root dispersion relation, which leads to a subleading logarithmic term in the entanglement entropy. All of these are confirmed by numerical calculations based on the Bogoliubov theory with the lowest-Landau-level approximation. Finally, we investigate the effects of quantum fluctuations on the phase diagrams by calculating the correction to the ground-state energy due to zero-point fluctuations in the Bogoliubov theory. We find that the boundaries between rhombic-, square-, and rectangular-lattice phases shift appreciably with a decrease in the filling factor.

  • Symmetry-protected topological phases and competing orders in a spin- 12 XXZ ladder with a four-spin interaction

    Ogino Takuhiro, Furukawa Shunsuke, Kaneko Ryui, Morita Satoshi, Kawashima Naoki

    Physical Review B (Physical Review B)  104 ( 7 )  2021年08月

    ISSN  2469-9950


    We study a spin-12 XXZ model with a four-spin interaction on a two-leg ladder. By means of effective field theory and matrix product state calculations, we obtain rich ground-state phase diagrams that consist of eight distinct gapped phases. Four of them exhibit spontaneous symmetry breaking with either a magnetic or valence-bond-solid (VBS) long-range order. The other four are featureless, i.e., the bulk ground state is unique and does not break any symmetry. The featureless phases include the rung singlet (RS) and Haldane phases as well as their variants, the RS∗ and Haldane∗ phases, in which twisted singlet pairs (|↑↓)+|↓↑))/2 are formed between the two legs. We argue and demonstrate that Gaussian transitions with the central charge c=1 occur between the featureless phases and between the ordered phases while Ising transitions with c=1/2 occur between the featureless and ordered phases. The two types of transition lines cross at the SU(2)-symmetric point, where the criticality is described by the SU(2)2 Wess-Zumino-Witten theory with c=3/2. The RS-Haldane∗ and RS∗-Haldane transitions give examples of topological phase transitions. Interestingly, the RS∗ and Haldane∗ phases, which have highly anisotropic nature, appear even in the vicinity of the isotropic case. We demonstrate that all the four featureless phases are distinguished by topological indices in the presence of certain symmetries.

  • Intercomponent entanglement entropy and spectrum in binary Bose-Einstein condensates

    Yoshino T., Furukawa S., Ueda M.

    Physical Review A (Physical Review A)  103 ( 4 )  2021年04月

    ISSN  2469-9926


    We study the entanglement entropy and spectrum between components in binary Bose-Einstein condensates in d spatial dimensions. We employ effective field theory to show that the entanglement spectrum exhibits an anomalous square-root dispersion relation in the presence of intercomponent tunneling (Rabi coupling) and a gapped dispersion relation in its absence. These spectral features are associated with the emergence of long-range interactions in terms of the superfluid velocity and the particle density in the entanglement Hamiltonian. Our results demonstrate that unusual long-range interactions can be emulated in a subsystem of multicomponent BECs that have only short-range interactions. We also find that for a finite Rabi coupling the entanglement entropy exhibits a volume-law scaling with subleading logarithmic corrections originating from the Nambu-Goldstone mode and the symmetry restoration for a finite volume.

  • Continuous phase transition between Néel and valence bond solid phases in a J−Q -like spin ladder system

    Ogino Takuhiro, Kaneko Ryui, Morita Satoshi, Furukawa Shunsuke, Kawashima Naoki

    Physical Review B (Physical Review B)  103 ( 8 )  2021年02月

    ISSN  2469-9950


    We investigate a quantum phase transition between a Néel phase and a valence bond solid (VBS) phase, each of which breaks a different Z2 symmetry, in a spin-1/2 two-leg XXZ ladder with a four-spin interaction. The model can be viewed as a one-dimensional variant of the celebrated J-Q model on a square lattice. By means of variational uniform matrix product state calculations and an effective field theory, we determine the phase diagram of the model and present evidence that the Néel-VBS transition is continuous and belongs to the Gaussian universality class with the central charge c=1. In particular, the critical exponents β,η, and, ν are found to satisfy the constraints expected for a Gaussian transition within numerical accuracy. These exponents do not detectably change along the phase boundary while they are in general allowed to do so for the Gaussian class.

  • Magnetoelastic study on the frustrated quasi-one-dimensional spin- 12 magnet LiCuVO4

    Miyata A., Hikihara T., Furukawa S., Kremer R. K., Zherlitsyn S., Wosnitza J.

    Physical Review B (Physical Review B)  103 ( 1 )  2021年01月

    ISSN  2469-9950


    We investigated the magnetoelastic properties of the quasi-one-dimensional spin-12 frustrated magnet LiCuVO4. Longitudinal-magnetostriction experiments were performed at 1.5 K in high magnetic fields of up to 60 T applied along the b axis, i.e., the spin-chain direction. The magnetostriction data qualitatively resemble the magnetization results, and saturate at Hsat≈54 T, with a relative change in sample length of ΔL/L≈1.8×10-4. Remarkably, both the magnetostriction and the magnetization evolve gradually between Hc3≈48 T and Hsat, indicating that the two quantities consistently detect the spin-nematic phase just below the saturation. Numerical analyses for a weakly coupled spin-chain model reveal that the observed magnetostriction can overall be understood within an exchange-striction mechanism. Small deviations found may indicate nontrivial changes in local correlations associated with the field-induced phase transitions.

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総説・解説等 【 表示 / 非表示

  • エンタングルメント・エントロピーと共形場理論

    古川俊輔, 白石潤一

    日本物理学会誌 69   541 - 546 2014年

    記事・総説・解説・論説等(学術雑誌), 共著

研究発表 【 表示 / 非表示

  • Magnetic properties of volborthite determined by a coupled-trimer model

    S. Furukawa and T. Momoi

    International Workshop on Microscopic Properties of Quantum Materials (Hokkaido University) , 



  • 結合トライマー模型によるボルボサイトの理論


    第17回量子スピン系研究会 (沖縄県那覇市ともかぜ振興会館およびオンライン) , 



  • 強磁性・反強磁性相互作用の競合する量子磁性体の理論的研究


    強磁場コラボラトリーセミナー(強磁場フォーラム フロンティア奨励賞 受賞講演) (東京大学 物性研究所) , 



  • Quantum entanglement in topological phases and symmetry-broken phases


    Quantum Information Entropy in Physics (京都大学 基礎物理学研究所) , 




    I will review some applications of entanglement entropy (EE) and entanglement spectra (ES) in quantum many-body systems. In a variety of topological phases, it has been found that the ES has a similar structure as the edge-mode spectrum. The "cut and glue" picture gives a physical explanation of this remarkable entanglement-edge correspondence [1]. I will explain a simple formulation of this picture based on two coupled (chiral) Tomonaga-Luttinger liquids [2]. The obtained ES can be used to derive the so-called topological entropy. In systems with continuous symmetry breaking, the EE shows a subleading logarithmic term whose coefficient is related to the number of Nambu-Goldstone modes [3]. Furthermore, the ES shows a "tower of states" structure reminiscent of the finite-size energy spectrum. I will explain the emergence of analogous features in the intercomponent entanglement in binary Bose-Einstein condensates [4].

    [1] X.-L. Qi, H. Katsura, and A.W.W. Ludwig, Phys. Rev. Lett. 108, 196402 (2012).
    [2] R. Lundgren, Y. Fuji, S. Furukawa, and M. Oshikawa, Phys. Rev. B 88, 245137 (2013).
    [3] M. A. Metlitski and T. Grover, arXiv:1112.5166.
    [4] T. Yoshino, S. Furukawa, and M. Ueda, Phys. Rev. A 103, 043321 (2021).

  • スピン1/2フラストレートXXZ梯子の基底状態相図

    荻野卓啓, 金子隆威, 森田悟史, 古川俊輔

    日本物理学会2021年秋季大会 (オンライン開催) , 



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競争的研究費の研究課題 【 表示 / 非表示

  • 人工ゲージ場中のボース・アインシュタイン凝縮体における多体効果の理論的研究


    慶應義塾, 学事振興資金, 古川俊輔, 補助金,  研究代表者

  • 対称性で多様化したトポロジカル相の基礎理論の構築と実現法の提案


    文部科学省・日本学術振興会, 科学研究費助成事業, 古川 俊輔, 基盤研究(C), 補助金,  研究代表者

  • 光格子中のボース・アインシュタイン凝縮体における位相フラストレーション


    松尾学術研究助成金, 古川俊輔, 補助金,  研究代表者

  • 強相関冷却原子系におけるトポロジカル秩序の探索とその基礎理論の構築


    東京大学, 古川 俊輔, 若手研究(B), 未設定



受賞 【 表示 / 非表示

  • 第2回強磁場フォーラムフロンティア奨励賞

    古川俊輔, 2020年12月, 強磁場フォーラム, 強磁性・反強磁性相互作用の競合する量子磁性体の理論的研究

    受賞区分: 国内学会・会議・シンポジウム等の賞



  • 第7回日本物理学会領域11若手奨励賞

    古川俊輔, 2013年03月, 日本物理学会, 量子多体系におけるエンタングルメント・エントロピーの研究

    受賞区分: 国内学会・会議・シンポジウム等の賞




担当授業科目 【 表示 / 非表示

  • 物理学演習第1


  • 物理学B


  • 物理学A


  • 物理数学


  • 論文講読発表


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所属学協会 【 表示 / 非表示

委員歴 【 表示 / 非表示

  • 2022年04月

    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年04月

    新著紹介小委員会 委員, 日本物理学会

  • 2020年04月

    領域3(磁性)運営委員, 日本物理学会