量子信息交叉中心学术报告006

Title: Violation of fluctuation-response relation in active systems

Speaker: Prof. Lei-Han Tang, Beijing Computational Science Research Center, and Department of Physics, Hong Kong Baptist University （汤雷翰教授，北京计算科学研究中心，香港浸会大学物理系)

Place:  RM 101，Bulg. 2，Xixi Campus (西溪校区西二楼101室)

Date and time: 14:00，April 1，2019 （4月1日下午14:00）

Abstract：The fluctuation-dissipation theorem (FDT), also known as the fluctuation-response relation (FRR), is a central result of statistical physics, which applies to any system at thermodynamic equilibrium. Its violation is a strong signature of nonequilibrium behavior. In active systems, which include most of life forms on earth but potentially also future man-made intelligent systems, energy is injected at small scales and used to drive larger scale nonequilbirum behavior. For active systems described by Langevin equation(s), the Harada-Sasa equality[1] relates FRR violation to the entropy production by the system. We have recently developed an adiabatic perturbative scheme that allows calculation of the frequency-resolved response and auto-correlations in time-scale separated systems[2]. We found the existence of a generic plateau regime for FRR violation in frequency space, which can be used to estimate entropy production due to coupling between fast and slow degrees of freedom. We also discuss the concept of an effective temperature for active systems upon coarse-graining in time, and give examples where the FRR either holds or is violated on the low frequency side.

[1]R Kubo, Rep. Prog. Phys. 29, 255 (1966).

[2]T Harada and S-I Sasa, Phys Rev Lett 95,130602 (2005).

[3]S-W Wang, K Kawaguchi, S-i Sasa, and L-H Tang, Phys Rev Lett 117, 070601 (2016).

汤雷翰博士简介：Dr. Tang completed his PhD in statistical physics at the Carnegie Mellon University in 1987. He did postdoctoral work on quasicrystals, growing surfaces, and other nonequilibrium and disordered systems at various US and German institutions including Texas A&M University, the Institute for Solid State Science at KFA Jülich and the Institute for Theoretical Physics at the University of Cologne. He was appointed Lecturer at the Imperial College of Science, Technology and Medicine in 1996 and subsequently joined the Physics Department at the Hong Kong Baptist University as Associate Professor and promoted to Professor in 2005. He joined the Beijing Computational Science Research Center in 2010 as the head of the Complex Systems Laboratory. He has also held visiting appointments at UCSF, Peking University, Sun Yat-Sen University, Zhejiang University and the University of Science and Technology of China. Dr. Tang’s research combines analytical and computational approaches to explore the effect of equilibrium and nonequilibrium fluctuations on the stability of ordered structures in various physical and biophysical contexts, in particular the energetics and dynamics of defects that disrupt ordering. In recent years, he has collaborated with experimentalists on the development of quantitative tools to analyze and integrate biological data and information.