Homodyne detection of coherence and phase shift of a quantum dot in a cavity.

A homodyne measurement technique is demonstrated that enables direct observation of the coherence and phase of light that passed through a coupled quantum dot (QD)-microcavity system, which in turn enables clear identification of coherent and incoherent QD transitions. As an example, we study the effect of power-induced decoherence, where the QD transition saturates and incoherent emission from the excited state dominates at higher power. Further, we show that the same technique allows measurement of the quantum phase shift induced by a single QD in the cavity, which is strongly enhanced by cavity quantum electrodynamics effects.

Fine tuning of micropillar cavity modes through repetitive oxidations.

Repetitive wet thermal oxidations of a tapered oxide aperture in a micropillar structure are demonstrated. After each oxidation step the confined optical modes are analyzed at room temperature. Three regimes are identified. First, the optical confinement increases when the aperture oxidizes toward the center. Then, the cavity modes shift by more than 30 nm when the taper starts to oxidize through the center, leading to a decrease in the optical path length. Finally, the resonance frequency levels off when the aperture is oxidized all the way through the micropillar, but confined optical modes with a high quality factor remain. This repetitive oxidation technique therefore enables precise control of the optical cavity volume or wavelength.