Multiphoton interaction of a qutrit with single-mode quantized field in the ultrastrong and deep strong coupling regimes

We consider the multiphoton dynamics of a quantum system composed of a three-state atom (a qutrit) and a single-mode photonic field in the ultrastrong and deep strong coupling regimes, when the coupling strength is comparable to or larger than the oscillator energy scale. We assume a qutrit to be in a L configuration, where an upper level is coupled to a twofold degenerate lower level. Direct multiphoton resonant transitions revealing generalized Rabi oscillations, collapse, and revivals in atomic excitation probabilities for the ultrastrong couplings are studied. In the deep strong coupling regime, particular emphasis is placed on the ground state of the considered system which strictly exhibits nonclassical properties. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)