Photon emission via vacuum-dressed intermediate states under ultrastrong coupling

Understand

We investigate theoretically quantum effects of a cavity-atom system in which the upper two levels of a cascade-type three-level atom interact with a cavity field mode in the ultrastrong coupling regime.

• By exploiting the virtual photons carried by atom-cavity dressed states, we indicate how two external driving fields induce Raman transitions such that a continuous conversion of virtual photons into real photons can be achieved with a high probability.
• We present analytical and numerical solutions of the system.
• In addition, we show that the converted photons exhibit a bunching behavior in the steady state.