The analytical eigenenergies and eigenstates of the Rabi model are obtained approximately based on a unitary transformation and a generalized rotating-wave approximation (GRWA). Using these analytical expressions without the rotating wave approximation (RWA), we generalize the definition of the physical emission spectrum valid with the RWA in order to meet without the RWA with some modifications. Taking into account the counter-rotating wave terms and the intercrossing of energy level in the strong coupling regime, the physical emission spectru...
