Effect of the third level on time evolution of the spontaneous upper level decay due to counter-rotating terms

The third level has great influence on the time evolution of the spontaneous decay from the excited state, when the counter-rotating terms are taken into account. The influence in the cascade-type and V-type three-level systems is investigated for two initial states, excited from the ground states of the whole system (atom plus vacuum modes) and from the bare atom. The third level results in the additional virtual photon processes, emitting a photon from one level and reabsorbing the same photon to another level and vice versa. The main influence of the third level is to accelerate the decay, which leads to or enhances the anti-Zeno effect, especially for the initial state excited from the ground state of the whole system. Therefore, the third level cannot be neglected, if the counter-rotating terms are taken into account.