Time-dependent Fr\"ohlich transformation approach for two-atom   entanglement generated by successive passage through a cavity
  Time-dependent Fr\"ohlich transformations can be used to derive an effective Hamiltonian for a class of quantum systems with time-dependent perturbations. We use such a transformation for a system with time-dependent atom-photon coupling induced by the classical motion of two atoms in an inhomogeneous electromagnetic field. We calculate the entanglement between the two atoms resulting from their motion through a cavity as a function of their initial position difference and velocity. 
Yong Li, C. Bruder, and C. P. Sun