Indistinguishable single photons from a quantum dot

We report a set of experiments designed to test the quantum indistinguishability of single photons emitted by a resonantly pumped InAs/GaAs quantum dot, embedded in a microcavity. We first performed high resolution interferometric measurements on the source to infer its coherence time. By comparison with the exciton lifetime, obtained by time-resolved spectroscopy, we found that some quantum dots were emitting almost transform-limited photons. The measured ratio of the coherence time to the pulse duration gives a lower bound on the dephasing time which agrees well with previous studies. We then directly measured the mean overlap between wave packets of consecutive photons emitted 2 ns apart, through a Hong-Ou-Mandel type two-photon interference experiment. For the best dot, an overlap as high as 0.81 was inferred. This result suggests that quantum dots could be a practical single photon source to perform quantum information processing experiments. We stress the importance of the microcavity for identical photon generation.