# Quantum phase transition and universal dynamics in the Rabi model

- Speaker: Myung-Joong Hwang (Univ of Ulm, Germany)
- Date: Monday February 16, 2016 17:00
- Place: Jeongho Seminar Room

In this talk, I will discuss our recent finding [1] that a two-level system coupled to a single-mode cavity field, described by the Rabi model, undergoes a second order quantum phase transition. Having only two constituent particles, the Rabi model is far from being in a thermodynamic limit; however, out study shows that an infinite ratio of the atomic transition frequency to the cavity frequency can play the role of thermodynamic limit. I first prove the quantum phase transition of the model by developing an effective low-energy theory for the infinite frequency-ratio limit. Then, in the sprit of finite-size scaling theory, I will discuss the influence of the criticality on a finite frequency-ratio limit by calculating finite-frequency exponents and scaling functions. This opens up a possibility to observe the evidence of the QPT in the Rabi model experimentally. Finally, going beyond the equilibrium setting, the influence of the quantum phase transition on the dynamics will be discussed. We show that Kibble-Zurek mechanism can precisely predict the universal scaling of the adiabatic dynamics of the Rabi model, which provides a first confirmation of the KZM prediction for a model without spatial degrees of freedom.

[1] Myung-Joong Hwang, Ricardo Puebla, and Martin B. Plenio, Phys. Rev. Lett. 115, 180404 (2015)