The dynamics of entanglement in two-atom Tavis-Cummings model with   non-degenerate two-photon transitions for tripartite entangled W-like states
  The influence of dipole-dipole interaction on the entanglement between two atoms with different initial entangled W-like states in Tavis-Cummings model with degenerate two-photon transitions has been investigated. The results show that the entanglement between two atoms can be increased by means of dipole-dipole interaction and for some initial states the entanglement sudden death effect can be weakened. 
E.K. Bashkirov, M.S. Mastyugin
quant-ph