Dynamical evolution of an inverted spin ensemble in a cavity:   Inhomogeneous broadening as a stabilizing mechanism
  We study the evolution of an inverted spin ensemble coupled to a cavity. The inversion itself presents an inherent instability of the system; however, the inhomogeneous broadening of spin-resonance frequencies presents a stabilizing mechanism, and a stability criterion is derived. The detailed behavior of mean values and variances of the spin components and of the cavity field is accounted for under both stable and unstable conditions. 
Brian Julsgaard and Klaus M{\o}lmer
quant-ph