应兰州大学物理学院赵继泽老师邀请，上海交通大学蔡子副教授举办线上学术报告。欢迎广大师生届时参加！

题目：Excitations in quantum time crystals

报告人：蔡子  副教授

时间：2020年10月23日下午15:00

线上地点：腾讯会议（会议ID：306 159 017）

会议链接：https://meeting.tencent.com/s/BtX3lDgF6AxV

线下地点：理工楼1215会议室

联系人：赵继泽

报告摘要:

        Spontaneous symmetry breaking and elementary excitation are two of the pillars of condensed matter physics that are closely related to each other. The symmetry and its spontaneous breaking not only control the dynamics and spectrum of elementary excitations, but also determine their underlying structures. In this paper, we study the excitation properties of a non-equilibrium quantum matter: a discrete time crystal phase that spontaneously breaks the temporal translational symmetry. It is shown that such an intriguing symmetry breaking allows an instanton-like excitation that represents a tunneling between two ``degenerate'' time crystal phases. Furthermore, we also observe a dynamical transition point at which the instanton ``size'' diverges, a reminiscence of the critical slowing down phenomenon in nonequilibrium statistic physics. A phenomenological theory has been proposed to understand the phase dynamics of the proposed system and the experimental realization and detection have also been discussed.

个人简介：

        Zi Cai received his bachelor his PhD in theoretical Physics by the Institute of Physics, Chinese Academy of Sciences in 2010. He was postdoc in the University of California at San Diego, University of Munich and the Institute of quantum optics of information, Austria Academy of Sciences before he joined Shanghai Jiao Tong University as a tenure track associate professor in 2016. He was selected as Young 1000 talent plan in 2017 and Shanghai 1000 talent plan in 2018. He work on several theoretical topics of quantum many-body physics focusing on open and non-equilibrium quantum systems, ultracold atoms as well as numerical strongly correlated physics.