主讲人：Sergej Flach 教授（韩国基础科学研究院）  

题目：Chaos and Thermalization  

时间：2024年07月22日上午09：00  

地点：理工楼1215  

报告摘要：  

We will discuss strategies to quantify the thermalization of isolated classical nonlinear many body systems. Generically the underlying Hamiltonian will be nonintegrable and the dynamics chaotic. A trajectory will endlessly scan the available phase space. From a practical perspective of an experimentalist, we can measure observables (aka functions on the phase space) and their temporal fluctuations. We then extract time scales from these fluctuations which will give us estimates of ergodization times TE – times up to which we have to wait to observe reasonable agreement between time averages and phase space averages of observables in agreement with the ergodic theory. Since there are infinitely many observables, we can produce infinitely many ergodization times. From a theorist perspective we can measure the entire Lyapunov spectrum and invert the exponents to obtain an entire spectrum of chaos time scales TL. Frequently studies quench the system into a specific initial state and evolve it in order to attempt to measure some thermalization time TQ. An early example is the Fermi-Pasta-Ulam-Tsingou (FPUT) paradox. How are all these time scale sets related to each other? Answers and surprises can be found when tuning the systems close to integrability where thermalization is expected to slow down. I will use FPUT, Toda, unitary circuit networks and Josephson junction network models as numerical platforms to investigate the above problems.  

个人简介：

Prof. Sergej Flach is the Director of the Center for Theoretical Physics of Complex Systems, established in December 2014. He earned both his M.A. and Ph.D. from the Dresden University of Technology in Germany between 1986 and 1989. After an Alexander-von-Humboldt fellowship at TU Munich and postdoctoral work at Boston University, he joined the Max Planck Society in 1994. From 2012 to 2016, he was a professor at the New Zealand Institute for Advanced Study. Prof. Flach's research focuses on nonlinear quantum and classical waves in complex systems, Fano resonances in nanoscale structures, and exciton-polariton Bose-Einstein condensates. He has over 240 publications and has received several awards, including the Stefanos Pnevmatikos Award for Nonlinear Science. He also serves on the editorial boards of major scientific journals and has coordinated numerous workshops and conferences.