Spontaneous emission properties of a quantum dot in an ultrahigh-Q cavity:: Crossover from weak- to strong-coupling states and robust quantum interference

We theoretically discuss spontaneous emission properties of a quantum dot embedded in an ultrahigh-Q microcavity, where a detuning between an excitation in the quantum dot and the cavity mode is taken into account. Both weak- and strong-coupling states are obtained under the ultrahigh-Q condition. In the high-Q weak-coupling case, the spontaneous emission spectrum shows a sharp dip, whose origin is a quantum interference. In the strong-coupling case, there is a region where both the Rabi splitting and the quantum interference contribute on an equal footing, referred to as a crossover region, where the spontaneous emission spectral shape is quite similar to that of the high-Q weak-coupling state. The quantum interference is robust against the detuning.