A semiconductor quantum dot in an open microcavity

A semiconductor quantum dot is an excellent source of single photons and also acts as host for a spin qubit. Significant challenges are to create an efficient single-photon source, to reduce the noise such that photons created far apart in time also exhibit two-photon interference, and to ensure that the spin retains its coherence as a string of photons is generated. Potentially, all these challenges can be met by embedding a gated quantum-dot in an open microcavity. Results are presented here in both the strong-coupling and weak-coupling regimes of cavity-QED. In the weak coupling regime, the system mimics closely a canonical "one-dimensional atom", and acts as a single-photon source with an end-to-end efficiency above 50%. Single-shot spin readout is achieved in the Faraday configuration in just a few nanoseconds. Fast and coherent spin rotations are achieved in the Voigt configuration by using a Raman laser, and the spin coherence is extended by cooling the nuclear spins.