Department of Physics, The University of Tokyo
go to 2018 2017 2016 2015 2014 2013 2012 2011 2010 2009 2008 2007 2006 2005 2004 2003 2002 2001
2019年度 / Academic Year 2019

研究室メンバーによるレギュラー・セミナー、 および、他研究室・機関からのゲスト・スピーカーのセミナーを開催しています。 レギュラー・セミナーは下記要領で行います。 ご興味ある方の参加、歓迎します。事前の連絡なく参加頂けますが、 夏学期の論文紹介ゼミについては発表者に連絡頂けましたら発表資料を必要分印刷します。

Access map:理学部1号館 (Faculty of Science Bldg. 1) / 理学部4号館 (Faculty of Science Bldg. 4)

夏学期 / Summer semester (April-July 2019)

<Regular seminars (review of seminal papers)>
    Each seminar starts from 13:00, Thursday @ #913, Faculty of Science Bldg. 1 (unless otherwise indicated).
<Seminars by guest speakers>
    June 14 (Fri.) Prof. Tanmoy Das (the Indian Institute of Science) 13:15- @ #447
    June 20 (Thu.) Mr. Kazuki Yokomizo (Tokyo Institute of Technology) 13:00- @ #913
    July 2 (Tue.) Prof. Keiji Saito (Keio University) 13:00- @ #447

April 18 (Thu) Naoto Kura
    "Proof of a theorem of A. N. Kolmogorov on the invariance of quasi-periodic motions under small perturbations of the Hamiltonian"
    V. I. Arnol'd, Russ. Math. Surv. 18, 9 (1963)

April 25 (Thu) Zhikang Wang
    "Supersymmetry and quantum mechanics"
    F. Cooper, A. Khare and U. Sukhatme, Phys. Rept. 251, 267-385 (1995)

May 2 (Thu) (National Holiday)

May 14 (Tue.) 13:00- @ #447, Faculty of Science Bldg. 1 Zongping Gong
    "Topological Gauge Theories and Group Cohomology"
    R. Dijkgraaf, and E. Witten, Commun. Math. Phys. 129, 393 (1990)
    "Symmetry protected topological orders and the group cohomology of their symmetry group"
    X. Chen, Z.-C. Gu, Z.-X. Liu, and X.-G. Wen, Phys. Rev. B 87, 155114 (2013)

May 16 (Thu) Kohei Kawabata
    "Topological field theory of time-reversal invariant insulators"
    X.-L. Qi, T. L. Hughes, and S.-C. Zhang, Phys. Rev. B 78, 195424 (2008)

May 23 (Thu) Takumi Yoshino
    "Entropy, entanglement, and area: analytical results for harmonic lattice systems"
    M. B. Plenio, J. Eisert, J. Dreißig, and M. Cramer, Phys. Rev. Lett. 94, 060503 (2005)
    "Entanglement-area law for general bosonic harmonic lattice systems"
    M. Cramer, J. Eisert, M. B. Plenio, and J. Dreißig, Phys. Rev. A 73, 012309 (2006)

May 30 (Thu) Norifumi Matsumoto
    "Locality in Quantum and Markov Dynamics on Lattices and Networks"
    M. B. Hastings, Phys. Rev. Lett. 93, 140402 (2004)

June 6 (Thu) Ryusuke Hamazaki
    "Semiclassical Foundation of Universality in Quantum Chaos"
    S. Müller, S. Heusler, P. Braun, F. Haake, and A. Altland, Phys. Rev. Lett. 93, 014103 (2004)
    "Periodic-orbit theory of universality in quantum chaos"
    S. Müller, S. Heusler, P. Braun, F. Haake, and A. Altland, Phys. Rev. E 72, 046207 (2005)

June 13 (Thu) Kangqiao Liu
    "Three faces of the second law. I. Master equation formulation"
    M. Esposito, and C. V. d. Broeck, Phys. Rev. E 82, 011143 (2010)
    "Three faces of the second law. II. Fokker-Planck formulation"
    C. V. d. Broeck, and M. Esposito, Phys. Rev. E 82, 011144 (2010)

2019/6/14 (Fri.) 13:15- @ #447, Faculty of Science Bldg. 1
speaker Prof. Tanmoy Das (the Indian Institute of Science)
title The non-Hermitian world
abstract Exploration of non-Hermitian systems dates back to the early days of quantum theory. However, the progress of this field has exploded in the recent years with the development of a parallel quantum theory, and experimental verifications. The key advantage is that the relaxation of the Hermiticity constraint opens up a huge phase space for many unique features that may or may not have any direct analog with the Hermitian counterparts. Furthermore, parity and time-reversal symmetries render a parallel quantum world with a new way of defining conservation laws and associated properties. With a short overview on these new developments, I shall focus the discussions on the new topological phases and non-Hermitian superconductors when Hermiticity constraint is removed and/or replaced with other symmetry constraints. I shall also touch upon some of the experimental demonstrations in Photonic crystals and future realization in quantum matters.
[1] A. Ghatak and T. Das, arXiv:1902.07972.
[2] A. Ghatak and T. Das, Phys. Rev. B 97, 014512 (2018).

2019/6/20 (Thu.) 13:00- @ #913, Faculty of Science Bldg. 1
speaker Mr. Kazuki Yokomizo (Tokyo Institute of Technology)
title Bloch Band Theory for Non-Hermitian Systems
abstract Non-Hermitian systems, which are described by non-Hermitian Hamiltonians have been attracting much attention. In particular, the bulk-edge correspondence has been intensively studied in topological systems. In contrast to Hermitian systems, it seems to be violated in some cases. The reasons for this violation is that the Bloch wave vector is treated as real in non-Hermitian systems similarly to Hermitian ones. In this presentation, we establish a generalized band theory in a one-dimensional tight-binding model. In particular, we explain how to determine the generalized Brillouin zone C_β for the complex Bloch wave number β=e^ik, k∈C. In contrast to Hermitian cases, where C_β is always a unit circle, in non-Hermitian systems, C_β is a closed curve, not necessarily a unit circle. Furthermore, we find that C_β can have cusps, and its shape depends on system parameters. A byproduct of our theory is that one can prove the bulk-edge correspondence between the winding number defined from C_β and existence of topological edge states in the one-dimensional non-Hermitian systems.

June 25 (Tue.) 13:00- @ #447, Faculty of Science Bldg. 1 Ziyin Liu
    "Brownian Motion of a Quantum Oscillator"
    J. Schwinger, J. Math. Phys. 2, 407 (1961)

June 27 (Thu) Shoki Sugimoto
    "Normal Form of Antiunitary Operators"
    E. P. Wigner, J. Math. Phys. 1, 409 (1960)

2019/7/2 (Tue.) 13:00- @ #447 , Faculty of Science Bldg. 1
speaker Prof. Keiji Saito (Keio University)
title Ensemble equivalence and eigenstate thermalization from clustering of correlation
abstract Clustering of an equilibrium bipartite correlation is widely observed in non-critical many-body quantum systems. In this talk, we consider the thermalization phenomenon in generic finite systems exhibiting clustering. We demonstrate that such classes of systems exhibit the ensemble equivalence between microcanonical and canonical ensembles even for subexponetially small energy shell with respect to the system size. Most remarkably, in low-energy regime, the thermalization for single eigenstate is proven. In this seminar, I will provide several examples satisfying the eigenstate thermalization. I will also explain several key-ingredients in mathematical aspect also.
Ref.: T. Kuwahara and KS, arXiv:1905.01886.

July 4 (Thu) Hiroto Takahashi
    "Topological semimetal and Fermi-arc surface states in the electronic structure of pyrochlore iridates"
    X. Wan, A. M. Turner, A. Vishwanath, and S. Y. Savrasov, Phys. Rev. B 83, 205101 (2011)

July 11 (Thu) Takuya Kamijima
    "Entropy production fluctuation theorem and the nonequilibrium work relation for free energy differences"
    G. E. Crooks, Phys. Rev. E 60, 2721 (1999)