where P j , Q j , and ω j are the momentum, coordinate, and frequency of the photon modes outside the cavity, and the coupling strength is specified by c j . We should mention that Eq. ( ) is usually termed as cavity loss, which would be more appropriate in the case where the cavity photon bath is Markovian and there is no reflux of the photon back into the cavity. The model in Eq. ( ) can be considered as an open quantum system, that is, a system of interest interacting with a macroscopic environment,