Photon Berry phases, Instantons, Schrodinger Cats with oscillating parities and crossover from $U(1)$ to $Z_2$ limit in cavity QED systems

Yu Yi-Xiang, Jinwu Ye, W. M. Liu +1

In this work, we study the $U(1)/Z_2$ Dicke model at a finite $N$ by using the $1/J$ expansion and exact diagonization. This model includes the four standard quantum optics m…