近畿大学理工学部物理学コースの量子制御研究室、量子多体物理学研究室、物性理論研究室が合同で運営する量子物理学および量子技術に関するセミナーです。学期中は基本的に毎週水曜日10:45-12:15に開催しています。
今後の予定
2023年度
前期
日時： 2023年5月24日10:45-
教室： 31号館3階シミュレーション実験室 + Zoomでのオンライン配信
発表者： Polo, Juan（Quantum Research Center, Technology Innovation Institute）
題目：Fractionalization of the angular momentum in SU(N) atomtronic circuits
概要：Neutral atoms guided in ring-shaped atomtronic circuits present quantized values of the angular momentum per particle. Depending on the specific parameters characterizing the system (eg: nature of the particle statistics, interactions), the winding number present different quantizion properties. In this talk, I will showcase how such a phenomenon occurs in an atomtronic circuit with a quantum fluid consisting of strongly interacting N component fermions, the so-called SU(N) fermions. For repulsive interactions a specific emerging phenomenon of attraction from repulsion appears, providing a quantization with similar properties to the attracting bosonic case. For attractive interactions, the quantization is determined by the number of components N . The suggested implementation of our work is provided by cold atoms therefore, I will also present how the fractionalization of the winding number can be read-out experimentally.
日時： 2023年5月31日10:45-
教室： 31号館3階シミュレーション実験室 + Zoomでのオンライン配信
発表者： 段下 一平（量子多体）
題目：Correlation-spreading dynamics after a quantum quench in low-dimensional Ising models with transverse field
概要：Recent advances in controlling and manipulating Rydberg atoms trapped with an optical tweezer array have made it possible to utilize this platform as a quantum simulator of quantum Ising models, where dynamics of spin-spin correlations can be measured at a single-site resolution. Motivated by such experimental development, we theoretically study dynamics of spatial spreading of equal-time spin-spin correlations in the transverse-field Ising model subjected to a sudden change of the transverse field [1]. We assume that the initial state is a state polarized completely along the transverse direction, which is the ground state in the large-field limit. In one spatial dimension (1D), we use the exact analytical method and the linear spin-wave approximation (LSWA). We compare the outputs of the former with those of the latter in order to show that the latter can quantitatively capture the exact group velocity of the correlations as long as the transverse-field after the quench is sufficiently large compared to the spin-spin interaction. However, it fails to capture the detailed time dependence of the correlation functions. In 2D, with use of LSWA, we give a specific estimate of the group velocity in the large-field region. We also utilize the projected entangled pair states algorithm in order to provide quantitatively accurate time-evolution of the correlation functions for a relatively short time.
[1] R. Kaneko and I. Danshita, arXiv:2301.01407 [cond-mat.quant-gas].
日時： 2023年6月14日10:45-
教室： 31号館3階シミュレーション実験室 + Zoomでのオンライン配信
発表者： Mikkelsen, Mathias（量子多体）
題目：TBA
概要：TBA
日時： 2023年6月21日10:45-
教室： 31号館3階シミュレーション実験室 + Zoomでのオンライン配信
発表者： 安藤 京介（物性理論）
題目：TBA
概要：TBA
日時： 2023年6月29日13:15-
教室： 31号館3階シミュレーション実験室 + Zoomでのオンライン配信
発表者： 武上 響生（京都大学）
題目：TBA
概要：TBA
日時： 2023年7月5日10:45-
教室： 31号館3階シミュレーション実験室 + Zoomでのオンライン配信
発表者： 數田 裕紀（量子多体）
題目：TBA
概要：TBA
日時： 2023年7月12日10:45-
教室： 31号館3階シミュレーション実験室 + Zoomでのオンライン配信
発表者： 木屋 晴貴（量子制御）
題目：TBA
概要：TBA
日時： 2023年7月19日10:45-
教室： 31号館3階シミュレーション実験室 + Zoomでのオンライン配信
発表者： 近藤 康（量子制御）
題目：TBA
概要：TBA
過去の講演
2023年度
前期
日時： 2023年4月19日10:45-
教室： 31号館3階シミュレーション実験室 + Zoomでのオンライン配信
発表者： 小久保 治哉（物性理論）
題目： Size dependence of the critical velocity for quantum vortex formation by the superfluid wake with a plate obstacle
概要： The wake generated by an object moving through a fluid depends on the size and velocity of the obstacle and is associated with various physical phenomena such as vortex formation and turbulent transition. The wake has been studied experimentally and theoretically in superfluids. In cold atomic systems, optical potentials have been used in superfluid wake experiments [1-2]. In numerical simulations [3-4], Gaussian potential is often assumed as obstacles. However, the dynamics of the wake and the critical velocity for vortex formation depend on the specifics of the obstacle potential, complicating the universal discussion. Plate obstacle is comparatively easy to handle both theoretically and numerically. The size of the obstacle can be characterized only by the width of the plate, making it easy to study its effects.In this study, the size dependence of the critical velocity for quantum vortex formulation in the wake of a 2D Bose-Einstein condensate with the plate obstacle is investigated.
[1]Woo Jin Kwon, Joon Hyun Kim, Sang Won Seo, and Y. Shin, Phys. Rev. Lett. 117, 245301 (2016)
[2]Younghoon Lim, et al, New J. Phys. 24, 083020 (2022)
[3]Kazuki Sasaki, Naoya Suzuki, and Hiroki Saito, Phys. Rev. Lett. 104, 150404 (2010)
[4]M. T. Reeves, et al, Phys. Rev. Lett. 114, 155302 (2015)
日時： 2023年4月26日10:45-
教室： 31号館3階シミュレーション実験室 + Zoomでのオンライン配信
発表者： 笠松 健一（物性理論）
題目： Recent understanding and problems on vortex dynamics in binary Bose-Einstein condensates
概要： I review some recent progress and remaining problems on the properties of quantized vortices in two-component (binary) Bose-Einstein condensates (BECs). A vortex in binary BECs takes a rich variety of structures, forming a half-quantized vortex, as a result of the presence of multiple order parameters. This vortex exhibits nontrivial structure and dynamics when we consider the system of several or lots of vortices. In this talk, we will discuss (i) Interactions and dynamics of two separated vortices [1,2], (ii) Structures of vortex lattices in a rotating potential [3], (iii) Quantum turbulence by stirring of a localized potential [4].
[1] K. Kasamatsu, M. Eto, and M. Nitta, Phys. Rev. A, 93, 013615 (2016).
[2] J. Han, K. Kasamatsu, and M. Tsubota, J. Phys. Soc. Jpn. 91, 024401 (2022).
[3] K. Kasamatsu, M. Tsubota and M. Ueda, Int. J. Mod. Phys. B 19, 1835 (2005).
[4] T. Mithun, K. Kasamatsu, B. Dey, and P. G. Kevrekidis, Phys. Rev. A 103, 023301 (2021).
日時： 2023年5月10日10:45-
教室： 31号館3階シミュレーション実験室 + Zoomでのオンライン配信
発表者： 鏡原 大地（量子多体）
題目：Classical simulation of non-Hermitian boson sampling dynamics using matrix product states
概要：Sampling complexity means the difficulty of sampling from a distribution close to the desired (e.g., quantum system) probability distribution and is discussed in the context of quantum supremacy. A famous example where sampling complexity is often discussed is boson sampling [1], which consists of sampling from the distribution of identical bosons generated by a linear interferometer. An interferometer is characterized by a unitary matrix. It is shown that boson sampling is hard by classical computers for random unitary matrices. Recently, by considering the sampling problem of identical bosons time-evolved by a quadratic Hamiltonian from a product state, a transition from the state where sampling can be done easily to one where it is difficult has been proposed [2]. Furthermore, it has been pointed out that when time evolution is extended to be non-unitary by considering open systems, there is a transition in sampling complexity that has not been observed in unitary systems [3].
In the previous QPT seminar, we studied the Rényi entanglement entropy in the non-Hermitian boson sampling dynamics discussed in Ref. [3] and found that low-entangled states appear in some parameter regions. In this talk, we consider a classical simulation using matrix product states (MPS) with the expectation that low-entangled states would be well described using MPS and therefore an efficient classical simulation of the sampling would be possible. We investigate the dynamics of the bond dimension, which corresponds to the number of Schmidt states kept in MPS, because it is closely related to the efficiency of sampling [4]. Our results clarify the region where an efficient classical simulation can be performed using MPS.
[1] S. Aaronson and A. Arkhipov, in Proceedings of the Forty-Third Annual ACM Symposium on Theory of Computing (Association for Computing Machinery, New York, 2011), pp. 333–342.
[2] A. Deshpande, B. Fefferman, M. C. Tran, M. Foss-Feig, and A. V. Gorshkov, Phys. Rev. Lett. 121, 030501 (2018).
[3] K. Mochizuki and R. Hamazaki, Phys. Rev. Res. 5, 013177 (2023).
[4] H.-L. Huang, W.-S. Bao, and C. Guo, Phys. Rev. A 100, 032305 (2019); C. Oh, K. Noh, B. Fefferman, and L. Jiang, Phys. Rev. A 104, 022407 (2021).