Dynamics of the Dicke model close to the classical limit

Abstract

We study the dynamical properties of the Dicke model for increasing spin length, as the system approaches the limit of a classical spin. First, we describe the emergence of collective excitations above the groundstate that converge to the coupled spin-oscillator oscillations found in the classical limit. The corresponding Green functions reveal quantum dynamical signatures close to the superradiant quantum phase transition. Second, we identify signatures of classical quasi-periodic orbits in the quantum time evolution using numerical time-propagation of the wave function. The resulting phase space plots are compared to the classical trajectories. We complete our study with the analysis of individual eigenstates close to the quasi-periodic orbits.