Influence of the External Classical Field on the Entanglement of a Two-Level Atom

The atomic and the field entropies of a two-level atom, which is additionally driven by an external classical field are investigated. Under a certain canonical transformation for the excited and ground states the system is transformed into the usual JCM. Using the equations of motion in the Heisenberg picture exact solutions for the time-dependent dynamical operators are obtained. The entanglement between atom-field system is studied by using the atomic and the field entropies. Also we use the concurrence to detect the sudden death phenomenon and the relationship between entropies and the concurrence of the entanglement are discussed. It is shown that the amount of entanglement, the atomic and the field entropies of the subsystem can be improved by controlling the external classical field.