Robust Entanglement in Atomic Systems via Lambda-Type Processes
  It is shown that the system of two three-level atoms in $\Lambda$ configuration in a cavity can evolve to a long-lived maximum entangled state if the Stokes photons vanish from the cavity by means of either leakage or damping. The difference in evolution picture corresponding to the general model and effective model with two-photon process in two-level system is discussed. 
Ozgur Cakir, M. Ali Can, Alexander Klyachko, and Alexander Shumovsky