Cavity-enhanced single photons from a quantum dot

Single-photon sources rarely emit two or more photons in the same pulse, compared to a Poisson-distributed source of the same intensity, and have numerous applications in quantum information science. The quality of such a source is evaluated based on three criteria: high efficiency, small multi-photon probability, and quantum indistinguishability. We have demonstrated a single-photon source based on a quantum dot in a micropost microcavity that exhibits a large Purcell factor together with a small multi-photon probability. For a quantum dot on resonance with the cavity, the spontaneous emission rate has been increased by a factor of five, while the probability to emit two or more photons in the same pulse has been reduced to 2% compared to a Poisson-distributed source of the same intensity. The indistinguishability of emitted single photons from one of our devices has been tested through a Hong-Ou-Mandel-type two-photon interference experiment; consecutive photons emitted from such a source have been largely indistinguishable, with a mean wave-packet overlap as large as 0.81. We have also designed and demonstrated two-dimensional photonic crystal GaAs cavities containing InAs quantum dots that exhibit much higher quality factors together with much smaller mode volumes than microposts, and therefore present an ideal platform for construction of single photon sources of even higher quality.