Dynamic effects of electromagnetic wave on a damped two-level atom

We studied the dynamic effects of an electromagnetic (EM) wave with circula r polarization on a two-level damped atom. The results demonstrate an inter esting ac Stark split of the energy levels of the damped atom. The split le vels have different energies and lifetimes, both of which depend on the int eraction and the damping rate of atom. When the frequency of the EM wave is tuned to satisfy the resonance condition in the strong coupling limit, the transition probability exhibits Rabi oscillation. Momentum transfer betwee n atom and EM wave shows similar properties as the tansition probability un der resonance condition. For a damped atom interacting with EM field, there exists no longer stable state. More importantly, if the angular frequency of the EM wave is tuned to be the same as the atomic transition frequency a nd its amplitude is adjusted appropriately according to the damping coeffic ients, we can prepare a particular 'Dressed State' of the coupled system be tween atom and EM field and can keep the system coherently in this 'Dressed state' for a very long time. This opens another way to prepare coherent at omic states. (C) 1999 Elsevier Science B.V. All rights reserved.