Dispersion in the driven dicke model

Abstract

An exact steady state solution for the atomic density operator is obtained for a model of N identical superimposed two- level atoms (the Dicke model) driven by a cw off-resonance laser field. Exact expressions are given then for the atomic observables and their fluctuations and for the atomic correlation functions for any N. The results show that the second order phase transition critical bifurcation point found in the resonant case and for N → ∞ disappears due to the dispersive (non- resonant) effects. This is confirmed, further, by an exact semiclassical analysis of the governing equations of motion.