Quantum entropy and entanglement in the Jaynes-Cummings model without the rotating-wave approximation

We have investigated the evolution of the field quantum entropy and the entanglement of the atom-field in the Jaynes-Cummings model without the rotating-wave approximation, and examined the effects of the virtual-photon processes (the counter-rotating terms) on the evolution of the field quantum entropy and the entanglement of the atom-field. Our results show that under the condition of the initial strong field, the virtual-photon processes play an important role for the evolution of the field quantum entropy and the entanglement between the atom and the field.