Phase Transition in a Two-level-cavity System in an Ohmic Environment

We propose that in the presence of an Ohmic, de-phasing type environment, a two-level-cavity system undergoes a quantum phase transition from a state with damped Rabi oscillation to a state without. We present the phase diagram and make predictions for pump and probe experiment. Such a strong coupling effect of the environment is beyond the reach of conventional perturbative treatment.