Evolution of the vacuum Rabi peaks in a many-atom system

The two peaks of the vacuum Rabi splitting behave like simple harmonic oscillators for very weak excitation. The transmission spectrum of a cavity filled with two-level atoms shows this doublet at low values of the driving intensity, but only a single peak at high values. The evolution from a doublet to a singlet is governed by the anharmonic response of the system as the driving intensity increases. The anharmonicity can grow to a point where frequency hysteresis appears in the transmission spectrum. This work investigates theoretically with a semiclassical model the transition from the doublet into the singlet. The stability of the different solutions is analysed as the parameters of atomic and cavity detuning vary. The model is extended to include the experimentally relevant transverse profile of the cavity mode as well as the standing wave structure of the field.