Yusuke Nakai

Name

Yusuke, Nakai (中井雄介)

Status

Present Affiliation

RIKEN (国立研究開発法人理化学研究所)
⊃ Pioneering Research Institute (開拓研究所)
⊃ Nonequilibrium Quantum Statistical Mechanics RIKEN Hakubi Research Team (濱崎非平衡量子統計力学理研白眉研究チーム )

Research fields and interests (ABC order)

Nonequilibrium phases of matter
Nonequilibrium statistical physics
Non-Hermitian physics
Quantum computation and quantum information
Strongly correlated electronic systems
Topological phenomena in condensed matter systems

E-mail

yusuke.nakai_AT_yukawa.kyoto-u.ac.jp
yusuke.nakai_AT_riken.jp

Please replace _AT_ by @.

Paper

〇Yusuke O. Nakai, Reuel Dsouza, Daichi Nakamura, Shu Hamanaka, Andreas P. Schnyder, Masatoshi Sato, ‘‘Callan-Rubakov effects in topological insulators’’, arXiv:2502.16729

The Callan-Rubakov effect describes monopole-catalyzed proton decay. While this effect is fundamental for quantum field theories, its experimental observation has remained far from reality. Here, we reveal a similar, but experimentally reachable, defect-catalysis of the quantum anomaly in topological materials. In particular, surface Dirac fermions on topological insulators develop a distinct localized state at the position of dislocations or π-fluxes, which mediates spin-flip time-reversal breaking scattering or absorption of electrons. Despite the Hermiticity of topological insulators, a non-Hermitian topological number guarantees the robust existence of the localized state. Our finding implies that non-magnetic defects may behave like magnetic impurities on surfaces of topological insulators. Using the K-theory classification, we generalize this condensed-matter version of the Callan-Rubakov effect to other classes of topological materials.

〇Yusuke O. Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘Topological enhancement of nonnormality in non-Hermitian skin effects’’, Phys. Rev. B 109, 144203 (2024). arXiv:2304.06689 [Selected as Editor’s Suggestion]

This paper introduces scalar measures that adequately characterize the non-Hermitian skin effects under the open boundary condition. Using these measures, we reveal that the topological properties of the non-Hermitian skin effect give a macroscopic enhancement of non-normality under the open boundary condition. The topological enhancement of non-normality governs the perturbation sensitivity of the spectra and the anomalous time-evolution dynamics intrinsic to non-Hermiticity. They also show that these measures correctly describe the disorder-induced topological phase transitions of the skin effect.

Colloquium / Seminar

〇Yusuke Nakai, Reuel Dsouza, Daichi Nakamura, Shu Hamanaka, Andreas Schnyder, Masatoshi Sato, ‘‘A new perspective on defects in topological insulators’’, ETH Zurich, Mar. 2025.
〇Yusuke Nakai, Reuel Dsouza, Daichi Nakamura, Shu Hamanaka, Andreas Schnyder, Masatoshi Sato, ‘‘A new perspective on defects in topological insulators’’, Frank Schindler's group seminar, Theory of Topological Matter, Imperial College London, Feb. 2025.
〇Yusuke Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘Topological enhancement of non-normality in non-Hermitian skin effects’’, Hatano laboratory Seminar, Institute of Industrial Science, University of Tokyo, Apr. 2024.
〇Yusuke Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘Enhanced non-normality in non-Hermitian skin effects’’, Quantum Many-Body Theory Group Seminar, Max Planck Institute for Solid State Research, Stuttgart, Germany, Feb. 2024.
〇Yusuke Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘Enhanced non-normality in non-Hermitian skin effects’’, RCNP Theory Seminar, Research Center for Nuclear Physics, Osaka University, Jan. 2024.
〇Yusuke Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘Topological enhancement of non-normality in non-Hermitian skin effects’’, Tohyama Lab, Applied Physics Seminar, Tokyo University of Science, Department of Applied Physics Japan, Oct. 2023.
〇Yusuke Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘Topological enhancement of non-normality in non-Hermitian skin effects’’, Solid State Theory Laboratory (Quantum Transport Theory Group) Seminar, Nagoya University, Department of Physics, Oct. 2023.

Oral presentation (International Conferences)

〇Yusuke Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘Topological enhancement of non-normality in non-Hermitian skin effects’’, Quantum Simulation of Novel Phenomena with Ultracold Atoms and Molecules, Kyoto, Japan, Apr. 2024.
〇Yusuke Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘Enhanced non-normality in non-Hermitian skin effects’’, APS March Meeting, Minneapolis, America, Mar. 2024.
〇Yusuke O. Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘Topological enhancement of non-normality in non-Hermitian skin effects’’, Physics of Open Systems & Beyond, Sapporo, Japan, Aug. 2023.
〇Yusuke Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘New characterization of non-Hermitian skin effects’’, APS March Meeting, Las Vegas, America, Mar. 2023.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘The stability of Z_2 skin effect in one dimension’’, International Seminar Dojo 2021 / Future Advanced Quantum Technology Workshop 2021, Online, Sep. 2021.

Poster presentation (International Conferences)

〇Yusuke Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘Topological enhancement of non-normality in non-Hermitian skin effects’’, Non-Hermitian topology, geometry and symmetry across physical platforms, New York, America, Sep. 2024.
〇Yusuke Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘Topological enhancement of non-normality in non-Hermitian skin effects’’, Quantum Information, Quantum Matter and Quantum Gravity, Kyoto, Japan, Sep. 2023.
〇Yusuke Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘Topological enhancement of non-normality in non-Hermitian skin effects’’, Non-Hermitian Topology: from Classical Optics to Quantum Matter, Dresden, Germany, Aug. 2023.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘New characterization of non-Hermitian skin effects’’, Novel Quantum States in Condensed Matter 2022, Kyoto, Japan, Nov. 2022.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘Topology and non-normality of non-Hermitian skin effects’’, International Seminar Dojo 2022 / Future Advanced Quantum Technology Workshop 2022, Kyoto, Japan, Sep. 2022.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘The characterization of non-Hermitian skin effects in disordered systems by non-normality’’, Localisation2022, Sapporo, Japan, Aug. 2022.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘The characterization of non-Hermitian skin effect in disordered systems by condition number’’, 29th International Conference on Low Temperature Physics, Sapporo, Japan, Aug. 2022.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘The competition skin modes and Anderson modes’’, International Symposia on Creation of Advanced Photonic and Electronic Devices 2022 and Advanced Quantum Technology for Future 2022, Online, Mar. 2022.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘The effects of disorder in non-hermitian skin effect in one dimension’’, EP2DS-24/MSS-20, Online, Nov. 2021.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘The construction of a topological number that can characterize skin effects in disordered one-dimensional systems’’, Stat&QuantPhys Autumn School 2021 (SQP2021), Online, Sep. 2021.

Oral presentation (Domestic Conferences)

〇Yusuke Nakai, Reuel Dsouza, Daichi Nakamura, Shu Hamanaka, Andreas Schnyder, Masatoshi Sato, ‘‘A new perspective on defects in topological insulators ~ Callan-Rubakov effects in topological insulators ~’’, JPS 2025 Spring Meeting, The Physical Society of Japan, Online, Mar. 2025.
〇Yusuke Nakai, Kenji Shimomura, Masatoshi Sato, ‘‘Enhanced non-normality in non-Hermitian skin effects’’, JPS 2024 Spring Meeting, The Physical Society of Japan, Online, Mar. 2024.
〇Yusuke Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘Non-normality enhancement in non-Hermitian systems’’, JPS 2023 Spring Meeting, The Physical Society of Japan, Online, Mar. 2023.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘The investigation of skin effects by dep’’, JPS 2022 Autumn Meeting Program, The Physical Society of Japan, Tokyo, Japan, Sep. 2022.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘The characterization of non-Hermitian skin effects by non-normality’’, The 67th Condensed Matter Physics Summer School, Online, Aug. 2022.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘The effects of disorder in non-Hermitian skin effect in one dimension’’, JPS 2021 Autumn Meeting, The Physical Society of Japan, The Physical Society of Japan, Online, Sep. 2021.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘The effects of disorder in non-Hermitian skin effect in one dimension’’, The 66th Condensed Matter Physics Summer School, Online, Aug. 2021.

Poster presentation (Domestic Conferences)

〇Yusuke Nakai, Nobuyuki Okuma, Daichi Nakamura, Kenji Shimomura, Masatoshi Sato, ‘‘Non-normality enhancement in non-Hermitian systems’’, Computational Physics Spring School, Okinawa, Mar. 2023.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘Analysis of stability against disorder in non-Hermitian skin effects’’, ISSP Workshops, Open system topology and biophysical/quantum/statistical physics, Chiba, Japan, Mar. 2022.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘On the stability of skin effect’’, JPS 77th Annual Meeting, The Physical Society of Japan, Online, Mar. 2022.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘Disorder effects for non-Hermitian skin effects’’, First Extreme Universe School, Online, Mar. 2022.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘The effects of disorder in non-Hermitian skin effect in one dimension’’, Quantum Theory of Thermal Fields and Its Applications, Online, Aug. 2021.
〇Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato, ‘‘Impurities effects in non-Hermitian skin effects’’, JPS 76th Annual Meeting, The Physical Society of Japan, Online, Mar. 2021.

Grants

Jun. 2024-Dec. 2024 Overseas Challenge Program for Young Researchers, Japan Society for the Promotion of Science (short-term scholar at Max Planck Institute for Solid State Research, Stuttgart, Germany), 1400,000 yen.
Apr. 2024- JST SPRING research grant, 300,000 yen.
Jul. 2023-Mar. 2024 Kyoto University WISE Program, Innovation of Advanced Photonic and Electronic Devices, Research Grant, 320,000 yen.
Jul. 2023-Mar. 2024 JST SPRING research grant, 300,000 yen.
Apr. 2023-Mar. 2024 JST SPRING, Grant Number JPMJSP2110, 400,000 yen.
Oct. 2022-Mar. 2023 Kyoto University WISE Program, Innovation of Advanced Photonic and Electronic Devices, Research Grant, 350,000 yen.
Apr. 2022-Mar. 2023 JST SPRING, Grant Number JPMJSP2110, 400,000 yen.
Apr. 2021- Kyoto University WISE Program, Innovation of Advanced Photonic and Electronic Devices.

Teaching Experience

Sep. 2023-Mar. 2024 Teaching Assistant, Faculty of Science, Kyoto University Fall semester: ‘‘Quantum mechanics III’’
Sep. 2022-Mar. 2023 Teaching Assistant, Faculty of Science, Kyoto University Fall semester: ‘‘Quantum mechanics III’’

Internship Experience

Sep. 2023-Oct. 2023 Quantum Computer Internship, Quantum Laboratory, Fujitsu Research, Fujitsu Limited.

Language

Japanese native
English conversational

Computer skills

OS: MacOS, Windows
Programming language: Python, LATEX, Julia, C, Fortran
Visualization: matplotlib
Text Editor: Visual Studio Code

公的業務補助等

西宮湯川記念国際滞在型研究会「Novel Quantum States in Condensed Matter 2022」運営補助業務（2022年10月〜2022年12月）．

Membership

Visits (more than 2 weeks)

Jun. 2024 - Dec. 2024 Max Planck Institute for Solid State Research, Stuttgart, Germany
Jan. 2024- Feb. 2024 Max Planck Institute for Solid State Research, Stuttgart, Germany

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