UEDA GROUP
Department of Physics, The University of Tokyo
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2017年度 / Academic Year 2017

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。
他研究室、他機関の方のセミナーも度々開催しています。

冬学期 / Winter semester (October 2017-Janurary 2018)

木曜日13:00から理学部1号館201a号室で行います(普段と場所or時間の異なる場合は赤字で示します)。
Every seminar starts from 13:00, Thursday @ #201a, Faculty of Science Bldg. 1 (unless otherwise indicated).
Oct. 2-3 Tokyo-Beijing Workshop
Oct. 5 Shuhei M. Yoshida / Sho Higashikawa
Oct. 12 Tomohiro Shitara / Ryusuke Hamazaki
Oct. 17-19 Intensive lecture by Prof. Masatoshi Sato
Oct. 26 Yuto Murashita / Kohei Kawabata
Nov. 2 Takumi Yoshino / Kazuya Fujimoto
Nov. 9 Zongping Gong / Shunsuke Furukawa
Nov. 15-16 Todai-ENS Workshop
Nov. 23 (National Holiday)
Nov. 30 Emi Yukawa / Shun Uchino
Dec. 7 (No Seminar)
Dec. 14 Yuto Ashida / Naoto Tsuji
Dec. 21 Naoto Kura / Junichi Iwasaki
Jan. 11 Zhikang Wang / Masaya Nakagawa
Jan. 18 (No Seminar)
Jan. 25 B4


夏学期 / Summer semester (April-August 2017)

木曜日13時から理学部1号館913号室で行います(普段と場所or時間の異なる場合は赤字で示します)。
Every seminar starts from 13:00, Thursday @ #913, Faculty of Science Bldg. 1 (unless otherwise indicated).
<Schedule>
July 4 Prof. Adolfo del Campo
July 24 Prof. Haruki Watanabe
August 24 Flore K. Kunst & Dr. Emil J. Bergholtz

April 13 (Thu) Zongping Gong
    "Coherence in Spontaneous Radiation Processes"
    R. H. Dicke, Phys. Rev. 93, 99 (1954)
    "Chaos and the quantum phase transition in the Dicke model"
    C. Emary and T. Brandes, Phys. Rev. E 67, 066203 (2003)
    "Dicke quantum phase transition with a superfluid gas in an optical cavity"
    K. Baumann, C. Guerlin, F. Brennecke, and T. Esslinger, Nature 464, 1301 (2010)

April 20 (Thu) Yuto Ashida
    "Matrix product states represent ground states faithfully"
    F. Verstraete and J. I. Cirac, Phys. Rev. B 73, 094423 (2006)
    "Solving the quantum many-body problem with artificial neural networks"
    G. Carleo and M. Troyer, Science 355, 602 (2017)
    "Neural network representation of tensor network and chiral states"
    Y. Huang and J. E. Moore, arXiv:1701.06246

April 27 (Thu) Sho Higashikawa
    "Absence of neutrinos on a lattice: (I). Proof by homotopy theory"
    H. B. Nielsen and M. Ninomiya, Nucl. Phys. B185, 20 (1981)
    "Absence of neutrinos on a lattice: (II). Intuitive topological proof"
    H. B. Nielsen and M. Ninomiya, Nucl. Phys. B193, 173 (1981)

May 4 (Thu) (National Holiday)

May 11 (Thu) (TMS International Conference)

May 18 (Thu) Ryusuke Hamazaki
    "A bound on chaos"
    J. Maldacena, S. H. Shenker, and D. Stanford, J. High Energy Phys. 08 (2016) 106

May 25 (Thu) Tomohiro Shitara
    "The large deviation approach to statistical mechanics"
    H. Touchette, Phys. Rep. 478, 1 (2009)

June 1 (Thu) (No Seminar)

June 8 (Thu) Yuto Murashita
    "Controlling chaos"
    E. Ott, C. Grebogi, and J. A. Yorke, Phys. Rev. Lett. 64, 1196 (1990)

June 15 (Thu) Shuhei M. Yoshida
    "Exponential expressivity in deep neural networks through transient chaos"
    B. Poole, S. Lahiri, M. Raghu, J. Sohl-Dickstein, and S. Ganguli, in Advances in Neural Information Processing Systems 29

June 22 (Thu) Naoto Kura
    "String-net condensation: A physical mechanism for topological phases"
    M. A. Levin and X.-G. Wen, Phys. Rev. B 71, 045110 (2005)

June 29 (Thu) Takumi Yoshino
    "Colloquium: Artificial gauge potentials for neutral atoms"
    J. Dalibard, F. Gerbier, G. Juzeliūnas, and P. Öhberg, Rev. Mod. Phys. 83, 1523 (2011)

2017/7/4 (Tue.) 15:00- @ #201b
speaker Prof. Adolfo del Campo (UMass Boston)
title Engineering Quantum Thermal Machines
abstract Quantum thermodynamics has emerged as an interdisciplinary research field in quantum science and technology with widespread applications. Yet, the identification of scenarios characterized by quantum supremacy - a performance without match in the classical world - remains challenging. In this talk I shall review recent advances in the engineering and optimization of quantum thermal machines. I will show that nonadiabatic many-particle effects can give rise to quantum supremacy in finite-time thermodynamics [1].
Tailoring such nonadiabatic effects by making use of shortcuts to adiabaticity, quantum heat engines can be operated at maximum efficiency and arbitrarily high output power [2]. A thermodynamic cost of these shortcuts will be elucidated by analyzing the full work distribution function and introducing a novel kind of work-energy uncertainty relation [3]. I shall close by discussing the identification of scenarios with a quantum-enhanced performance in thermal machines run over many cycles [4].
[1] J. Jaramillo, M. Beau, and A. del Campo, New J. Phys. 18, 075019 (2016).
[2] M. Beau, J. Jaramillo, and A. del Campo, Entropy 18, 168 (2016).
[3] K. Funo, J.-N. Zhang, C. Chatou, K. Kim, M. Ueda, and A. del Campo, Phys. Rev. Lett. 118, 100602 (2017).
[4] G. Watanabe, B. P. Venkatesh, P. Talkner, and A. del Campo, Phys. Rev. Lett. 118, 050601 (2017).

July 6 (Thu) Kohei Kawabata
    "Statistical Theory of Equations of State and Phase Transitions. I. Theory of Condensation"
    C. N. Yang and T. D. Lee, Phys. Rev. 87, 404 (1952)
    "Statistical Theory of Equations of State and Phase Transitions. II. Lattice Gas and Ising Model"
    T. D. Lee and C. N. Yang, Phys. Rev. 87, 410 (1952)

July 13 (Thu) Taisuke Matsuda
    "Dynamical Model of Elementary Particles Based on an Analogy with Superconductivity. I"
    Y. Nambu and G. Jona-Lasinio, Phys. Rev. 122, 345 (1961)
    "Dynamical Model of Elementary Particles Based on an Analogy with Superconductivity. II"
    Y. Nambu and G. Jona-Lasinio, Phys. Rev. 124, 246 (1961)

July 20 (Thu) Norifumi Matsumoto
    "Quantized Hall Conductance in a Two-Dimensional Periodic Potential"
    D. J. Thouless, M. Kohmoto, M. P. Nightingale, and M. den Nijs, Phys. Rev. Lett. 49, 405 (1982)
    "Topological invariant and the quantization of the Hall conductance"
    M. Kohmoto, Ann. Phys. 160, 343 (1985)

2017/7/24 (Mon.) 13:00-14:30 @ #1220(Faculty of Science Bldg. #4)
speaker Prof. Haruki Watanabe (UTokyo)
title 空間群の対称性に基づいた量子相の一般的な理解
abstract 量子多体系の基底状態や低エネルギー励起状態といった巨視的な(IRの)性質を、系の対称性や粒子数密度という微視的な(UVの)情報だけから、どこまで一般的に理解・予言できるだろうか。本講演の前半では、Lieb-Schultz-Mattis (Oshikawa-Hastings)定理を(磁気)空間群の仮定のもとに改良し、与えられた対称性・粒子数密度に対してどのような基底状態・低エネルギー励起が可能であるかを制限し、量子スピン液体を含むトポロジカル秩序相への応用を議論する[1]。
後半では特に自由粒子系のバンド構造に焦点を絞り、空間群の対称性やその表現に基づいてバンド構造のトポロジカルな性質を一般的にどのように理解できるかを議論する[2]。よく知られているように、Z2トポロジカル絶縁体の指標はもともとPfaffianをk空間で積分したもので与えられるが、系が反転対称性を有する場合にはこの煩雑な計算を実行する必要はなく、TRIMにおける占有軌道のパリティを掛け合わせればよい。この「反転対称性のパリティに基づくトポロジカル絶縁体の指標」を1651個の磁気空間群それぞれに拡張した「空間群の表現に基づくトポロジカル結晶絶縁体・トポロジカル半金属の指標」について説明し、興味深い具体例をいくつか議論する。
[1] H. Watanabe, H. C. Po, A. Vishwanath, and M. P. Zaletel, Proc. Natl. Acad. Sci. U.S.A. 112, 14551 (2015); H. C. Po, H. Watanabe, C.-M. Jian, and M. P. Zaletel, arXiv:1703.06882. 日本物理学会誌 2017年1月号に解説あり。
[2] H. Watanabe, H. C. Po, M. P. Zaletel, and A. Vishwanath, Phys. Rev. Lett. 117, 096404 (2016); H. C. Po, H. Watanabe, M. P. Zaletel, and A. Vishwanath, Sci. Adv. 2, e1501782 (2016); H. C. Po, A. Vishwanath, and H. Watanabe, Nat. Commun. 8, 50 (2017); H. Watanabe, H. C. Po, and A. Vishwanath, arXiv:1707.01903.

2017/8/24 (Thu.) 13:00-15:00 @ #201a
speaker Flore K. Kunst (Stockholm University / Freie Universitat Berlin)
title Anatomy of Topological Flat and Surface States: Exact Solutions from Destructive Interference on Frustrated Lattices
abstract The main feature of topological phases is the presence of robust boundary states, which appear for example in the form of chiral edge states in Chern insulators and open Fermi arcs on the surfaces of Weyl semimetals. Even though, non-interacting, topological systems can be straightforwardly described in fully periodic systems, the detail of the corresponding boundary states has mainly relied on numerical studies. In our work, we present a general method on how to find exact, analytical solutions for topological as well as trivial boundary states using a generic tight-binding model on a large class of geometrically frustrated lattices without the necessity of having to fine-tune hopping amplitudes. Our method is inspired by a similar approach that has been used in the past to construct, topologically-trivial, flat band models from local constraints on ‘line graphs’, in which case fine-tuning is required in the sense that hopping is strictly local. We expand on this work by considering a larger class of lattices, finding solutions for both topologically trivial and non-trivial bands, and going beyond the need for fine-tuning. In this sense, it is likely that our work will contribute to both the research fields of flat-band physics and that of topological matter, as well as advance the cross-fertilization between them. In my talk, I will present a number of examples to illustrate our discoveries, some of which are experimentally relevant such as the derivation of exact solutions for Fermi arcs in the recently synthesized slabs of pyrochlore iridates.

speaker Dr. Emil J. Bergholtz (Stockholm University / Freie Universitat Berlin)
title Fractional Chern insulators: From higher Chern number phases to non-Abelian twist defects
abstract In this talk I will discuss fractional Chern insulators with emphasis on the analogy with more conventional continuum Landau level physics — and on aspects that are qualitatively new in the lattice setting such as Berry curvature fluctuations, competing instabilities and novel collective states of matter emerging in bands with higher Chern number. I will also explain how the lattice setting naturally allows for exotic extrinsic wormhole-like twist defects (aka “genons”) that effectively increase the genus of space.