The Husimi distribution, the Wehrl entropy and the superradiant phase in   spin-boson interactions
  We study the Husimi distribution of the ground state in the Dicke model of field-matter interactions to visualize the quantum phase transition, from normal to superradiant, in phase-space. We follow an exact numerical and variational analysis, without making use of the usual Holstein-Primakoff approximation. We find that Wehrl entropy of the Husimi distribution provides an indicator of the sharp change of symmetry trough the critical point. Additionally, we note that the zeros of the Husimi distribution characterize the Dicke model quantum phase transition. 
R. del Real, M. Calixto and E. Romera
quant-ph math-ph math.MP