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。 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 2025)
<Regular seminars (review of seminal papers)>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)。
Each seminar starts from 13:00, Thursday @ #913, Faculty of Science Bldg. 1 (unless otherwise indicated).
<Schedule>
Apr. 10 Oyaizu
"Infinite Number of Order Parameters for Spin-Glasses"
G. Parisi, Phys. Rev. Lett. 43, 1754 (1979).
"The order parameter for spin glasses: a function on the interval 0-1"
G. Parisi, J. Phys. A: Math. Gen. 13 1101 (1980).
"Order Parameter for Spin-Glasses"
G. Parisi, Phys. Rev. Lett. 50, 1946 (1983).
Apr. 17 Sugiura
"Theory of Superconductivity"
J. Bardeen, L. N. Cooper, and J. R. Schrieffer, Phys. Rev. 108, 1175 (1957).
Apr. 24 Shiraishi
"The Theory of a General Quantum System Interacting with a Linear Dissipative System"
R. P. Feynman and F. L. Vernon Jr. J. Annals of Physics, 24, 118-173 (1963).
May 1 (No seminar)
May 8 (No seminar)
May 15 Hongchao Li
"Existence of Long-Range Order in One and Two Dimensions"
P. C. Hohenberg, Phys. Rev. 158, 383 (1967).
"Absence of Ferromagnetism or Antiferromagnetism in One- or Two-Dimensional Isotropic Heisenberg Models"
N. D. Mermin and H. Wagner, Phys. Rev. Lett. 17, 1133 (1966).
"Long-Range Orders in Ground States and Collective Modes in One- and Two-Dimensional Models"
S. Takada, Prog. Theor. Exp. Phys. 54, 1039-1049 (1975).
May 22 Ishii
"Dynamical Scaling of Growing Interfaces"
Mehran Kardar, Giorgio Parisi, and Yi-Cheng Zhang, Phys. Rev. Lett. 56, 9 (1986).
May 29 (No seminar)
Jun. 5 Hokkyo
"An Area Law for One Dimensional Quantum Systems"
M. B. Hastings, J. Stat. Mech. 2007, P08024 (2007).
Jun. 12 (No seminar)
Jun. 19 (No seminar)
Jun. 26 Yamada
"Black holes as mirrors: quantum information in random subsystems"
P. Hayden and J. Preskill, J. High Energy Phys. 2007, 120 (2007).
Jul. 3 Iyama
"Theory of dynamic critical phenomena"
P. C. Hohenberg and B. I. Halperin, Rev. Mod. Phys. 49, 3 (1977).
冬学期 / Winter semester (October 2025-January 2026)
木曜日13時から理学部１号館414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)。Each seminar starts from 13:00, Thursday @ #414, Faculty of Science Bldg. 1 (unless otherwise indicated).
<Schedule>
10/2 (No seminar)
10/9 Shiraishi / Oyaizu (@913)
10/16 (No seminar)
10/23 (No seminar)
10/30 Ming Gong
11/6 (No seminar)
11/13 Hongchao Li (from 16:00)
11/20 Hokkyo
11/27 (No seminar)
12/4 (No seminar)
12/11 (No seminar)
12/18 Sugiura
12/25 Nakagawa
1/1 (No seminar)
1/8 Kai Li (@233)
1/15 Nakanishi / Ishii (@TBA)
1/22 Yamada (@233)
1/29 Iyama (@233)
| speaker | Shiraishi |
| title | Quantum master equation approach to electron systems driven by external field or temperature difference |
| abstract | Abstract |
| speaker | Oyaizu |
| title | Chaotic RG flows in non-unitary quantum dynamics |
| abstract | One of the most important concepts that underlies the success of renormalization groups (RG) is the universality, where microscopic perturbations do not affect the macroscopic property dramatically. In the language of RG theory, this can be understood by the fact that different systems flows a same fixed point. However, as already pointed out in Wilson's series of papers [1], the convergence of RG flows are not obvious a priori, and a chaotic RG flow without any fixed points is in principle possible. Indeed, it is pointed out, by a simple example of a classical 1D Ising chain under imaginary magnetic field, that if we allow non-Hermiticity in a system, we can easily make the associated RG flows chaotic [2]. However, such a non-Hermiticity is usually difficult to introduce in a real system, and apart from few known examples [3], it has been unclear whether such chaotic RG flows are relevant to a more physical system. Moreover, the physical mechanism of how non-Hermiticity gives rise to chaotic RG flows has remained largely elusive. In this work [4], we first uncover a duality mapping that enables a physical implementation of a non-Hermitian spin chain by nonunitary quantum dynamics. Moreover, by using it, we show that even a single qubit dynamics can accompany such chaotic RG flow in its dynamics. Finally, we reveal the clear physical picture behind the presence of chaotic RG flow in the dynamics. [1] K. G. Wilson, Phys. Rev. B 4, 3174 (1971); Phys. Rev. B 4, 3184 (1971); Wilson & Kogut, Phys. Rep. 12, 2 (1974). [2] Dolan, Phys. Rev. E 52, 4512 (1995). [3] McKay, Berker & Kirkpatrick, Phys. Rev. Lett. 48, 767 (1982), Ilderton, Phys. Rev. Lett. 125, 130402 (2020); Jiang, Qiao & Lan, Phys. Rev. E 103, 062117 (2021). [4] Oyaizu, Li, Nakagawa & Ueda, in preparation. |
| speaker | Ming Gong |
| title | A Quantum Circuit Viewpoint on Mesoscopic Partition Noise |
| abstract | Current noise is a key signal revealing the nature of charge carriers and transport processes. In mesoscopic physics it typically has two contributions: thermal (Johnson–Nyquist) noise and shot noise. In a typical quantum Hall beam splitter, electrons undergo coherent quantum scattering and are partitioned at the outputs, and the partition shot noise can be detected at the receiver even at zero temperature. It is commonly believed that dephasing and relaxation suppress partition noise, an intuition often modeled with the Büttiker-probe approach. However, recent developments show that treating scattering fully quantum mechanically—mapping channels and scattering processes to monitored quantum circuits—can lead to different conclusions; for example, dephasing alone does not suppress shot noise. In this seminar, I will first review the basics of current noise in mesoscopic systems, then introduce recent progress on partition noise from the quantum-circuit perspective. Next, I will outline the conventional understanding when strong energy relaxation is introduced. Finally, I will present our scheme that integrates energy relaxation into the quantum-circuit representation and emphasize our finding that, under strong energy relaxation, shot noise can be fully suppressed, whereas thermal noise cannot; instead, it is partitioned. [1] C. W. J. Beenakker and J.-F. Chen. "Monitored quantum transport: full counting statistics of a quantum Hall interferometer." Quantum 9, 1874 (2025). [2] C. W. J. Beenakker. "Pure dephasing increases partition noise in the quantum Hall effect." arXiv: 2509.10242v1. [3] A. Shimizu and M. Ueda. "Effects of dephasing and dissipation on quantum noise in conductors." Phys. Rev. Lett. 69, 1403 (1992). |
| speaker | Hongchao Li |
| title | Optimizing digital quantum simulation of open quantum lattice models |
| abstract | Simulating quantum many-body systems, as a central topic of high- and low-energy physics, is one of the tasks that quantum computers are naturally suited to solving due to the exponential-to-polynomial speed-ups. Substantial effort has been put into designing quantum algorithms for simulating many-body systems. The state-of-the-art techniques, including the Trotterization methods [1] and quantum signal processing [2], now achieve provably nearly optimal scaling of both geometrically local gate count and parallelized circuit depths with respect to system size and target precision. However, in practice, most physical systems inevitably interact with their surrounding environment, and need to be described as an open quantum system. While near-optimal algorithms have been developed for simulating many-body quantum dynamics, algorithms for their open system counterparts remain less well investigated. In this work [3], we have addressed the problem of simulating geometrically local many-body open quantum systems interacting with a stationary Gaussian environment. Under a smoothness assumption on the system-environment coupling, we develop nearly optimal algorithms for the simulation of non-Markovian dynamics. We additionally show that, if only simulating local observables is of interest, then the circuit depth of the digital algorithm can be chosen to be independent of the system size by introducing the Lieb-Robinson bound of the system. Finally, for the Markovian dynamics with commuting jump operators, we propose two algorithms based on a locally dilated Hamiltonian construction and on sampling a Wiener process, respectively. These algorithms reduce the asymptotic gate complexity on the system size compared to currently available algorithms in terms of the required number of geometrically local gates. [1]: A. M. Childs and Y. Su, Phys. Rev. Lett. 123, 050503 (2019). [2]: J. Haah, M. B. Hastings, R. Kothari, and G. H. Low, SIAM Journal on Computing 35, FOCS18 (2021). [3]: X. Yu, H. Li, J. I. Cirac and R. Trivedi, arXiv: 2509.02268. |