Mean field description of the Dicke Model
  A mean field description of the Dicke model is presented, employing the Holstein-Primakoff realization of the angular momentum algebra. It is shown that, in the thermodynamic limit, when the number of atoms interacting with the photons goes to infinity the energy surface takes a simple form, allowing for a direct description of many observables. 
Jorge G. Hirsch, Octavio Castanos, Ramon Lopez-Pena, and Eduardo   Nahmad-Achar
quant-ph