Entanglement dynamics of two independent Jaynes-Cummings atoms without the rotating-wave approximation

Entanglement evolution of two independent Jaynes-Cummings atoms without rotating-wave approximation (RWA) is studied by an numerically exact approach. The previous results in the RWA are essentially modified in the strong coupling regime ($g\ge 0.1$), which has been reached in the recent experiments on the flux qubit coupled to the LC resonator. For the initial Bell state with anti-correlated spins, the entanglement sudden death (ESD) is absent in the RWA, but does appear in the present numerical calculation without RWA. Aperiodic entanglement evolution in the strong coupling regime is observed. The strong atom-cavity coupling facilitates the ESD. The sign of detuning play a essential role in the entanglement evolution for strong coupling, which is irrelevant in the RWA. An analytical results based on an unitary transformation are also given, which could not modify the RWA picture essentially. It is suggested that the activation of the photons may be the origin of the ESD. The present theoretical results could be applied to artificial atoms realized in recent experiments.