Entanglement Swapping: Entangling Atoms That Never Interacted
  In this paper we discuss four different proposals of entangling atomic states of particles which have never interacted. The experimental realization proposed makes use of the interaction of Rydberg atoms with a micromaser cavity prepared in either a coherent state or in a superposition of the zero and one field Fock states. We consider atoms in either a three-level cascade or lambda configuration 
E. S. Guerra and C. R. Carvalho