Entanglement of Atoms with Vacuum in Jaynes Cummings Model

We investigate the conditions for entanglement in a system of two atoms and two photon modes with a vacuum, using the Jaynes-Cummings model in the rotating-wave approximation. The results of previous studies are generalized to the case of non-resonant conditions. It is found that the strength of entanglement in atoms is a periodic function of time, in general. We explicitly show that our results are in agreement with existing results and reproduce the existing entanglement conditions under appropriate limits.