In this book, we study the system that consists of a two 2-level atoms interacting with a single-mode or two-mode quantized radiation field in the absent or presence of the Stark shift. Both atoms are prepared initially in the exited state and the field in a coherent state. An analytical solution for the system of two identical 2-level atom is obtained. The phase distribution, phase variance and Wigner function are investigated. The influence of the Stark shift on the Wigner function and the phase properties is analyzed. We investigate the purity loss of the system and bipartite partitions of...