学　术

　　由基础与前沿研究院主办的“基础论坛”第156期邀请到北京计算科学研究中心Stefano Chesi博士来校作学术交流。具体安排如下，欢迎师生们参加。

　　一、题　目：Quantum phase transition in the anisotropic Rabi model

　　二、时　间：2019年3月25日（周一）10:30

　　三、地　点: 沙河校区　通信楼818会议室

　　四、报告摘要

　　The quantum Rabi model (QRM) describes a two-level system interacting with a bosonic mode and is one of the simplest models of light-matter interactions. If the coupling strength is small, the QRM can be approximated by the even simpler Jaynes-Cummings (JC) model, where counter-rotating terms are neglected. Although these models have only few degrees of freedom, recent work has shown that a suitable limit of both the QRM and JC model displays a quantum phase transition similar to Dicke superradiance. In this talk we extend these results to the anisotropic QRM, where rotating- and counter-rotating terms have different weights. This question is important since typical realizations of strong light-matter interactions(e.g., in circuit QED) have quite naturally a finite anisotropy. Furthermore, the quantum phase transition has different universal properties in the known JC and QRM limits. Through a combination of analytic and numerical approaches we compute phase diagram, scaling functions, and critical exponents, which allow us to establish that the universality class at finite anisotropy is the same of the QRM. We also find other interesting features, like a superradiance-induced freezing of the effective mass and discontinuous scaling functions in the JC limit. Finally, by extending our study to a finite number of two-level systems, we demonstrate the full equivalence between the few-body quantum phase transition and regular Dicke superradiance occurring in the thermodynamic limit .

　　五、主讲人简介    

　　Stefano Chesi received his Ph.D. (2007) from Purdue University. He subsequently held postdoctoral positions in the University of Basel (2007-2011) and McGill University (2011-2013). In 2013 he became Research Scientist in RIKEN, Japan. 

　　Research Interests： 

　　Theoretical Condensed Matter Physics

　　Coherent spin phenomena in nanostructures

　　Quantum Information based on semiconductor systems

　　Electron correlations in the solid-state

　　　　　　　　　　　　　　　　　　　　　　　　　基础与前沿研究院

　　　　　　　　　　　　　　　　　　　　　　　　　　2019年3月22日