Spontaneous dressed-state polarization of a coupled atom and cavity mode

The authors calculate the asymptotic quantum state of a driven cavity mode interacting with a two-state atom when the dipole coupling constant is much larger than the atomic and cavity linewidths. They show that a novel symmetry breaking transition occurs as the strength of the driving field is increased. Although the driving field, the cavity mode, and the atom are all resonant, above the transition threshold the intracavity field shows a bimodality in phase. The bimodality results from an intensity-dependent detuning between the driving field and the transition frequencies of the composite atom-cavity-mode 'molecule.' Well above the transition threshold the driven cavity mode plus atom behaves as a driven harmonic oscillator with randomly switched detuning; the detuning (and hence the phase of the interactivity field) changes sign each time the atom makes a spontaneous transition between dressed states.