CMSP Seminar Series @ICTP Stasi Seminar Room Thursday 16 February at 11:30: Stefano CHESI

[Condensed Matter Section]

ICTP Seminar Series in Condensed Matter and Statistical Physics
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Thursday 16 February at 11:30 a.m.

Luigi Stasi Seminar Room, first floor, ICTP Leonardo building
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Speaker: Stefano CHESI (CSRC, Beijing, People's Republic of China)

Title: Quantum Phase Transition in the Anisotropic Rabi Model

Abstract: The quantum Rabi model (QRM) describes a two-level system 
interacting with a bosonic mode and it is one of the simplest models of 
light-matter interactions. If the coupling strength is small, the QRM 
can be approximated by the 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 [1] and JC model [2] 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) naturally 
have finite anisotropy. Furthermore, the quantum phase transition has 
different universal properties in the known JC and isotropic QRM limits. 
Through a combination of analytic and numerical approaches we compute 
phase diagram, scaling functions, and critical exponents, which allows 
us to establish that the universality class with 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.

[1] M.-J. Hwang, R. Puebla, and M. B. Plenio, Phys. Rev. Lett. 115, 
180404 (2015).
[2] M.-J. Hwang and M. B. Plenio, Phys. Rev. Lett. 117, 123602 (2016).