On evolution of the purity of two nonidentical two-level atoms   interecting with one-mode coherent field
  The resonant interaction of two nonidentical two-level atoms with one mode of the electromagnetic field has been considered. The pure-state evolution of the atomic states for field initially in the coherent state and atoms in the ground state has been investigated. It has been shown that for intermediate values of the relative differences of two coupling constants the atoms as well as the field are returned most closely to a pure state at the revival time. The possibility of the maximally entangled states at the beginning of the collapse time has been discussed. 
E.K. Bashkirov