A bright and fast source of coherent single photons

Semiconductor quantum dots (QDs) are potentially ideal emitters for realizing on-demand sources of indistinguishable single photons due to their large optical dipole moment and the low noise of the host material. A key challenge is to extract the photons and couple them efficiently into a single-mode optical fibre. So far end-to-end efficiency in such systems is low, restricting applications in single-photon-based quantum technologies.
In this work, we present a single-photon source with end-to-end efficiency of ~57%, more than 2x the prior state-of-the-art. This efficiency represents the probability of creating a single photon state at the output of the final optical fibre following pulsed excitation. Such performance is obtained with a tunable microcavity, a highly miniaturised Fabry-Perot cavity. The cavity is tunable in both frequency and antinode-position, and allows the QDs to be embedded in a p-i-n diode, which facilitates deterministic charging of the QDs and low-noise environment.
We measure a single-photon rate of 43.5 MHz under pulsed excitation (repetition rate = 76 MHz), accompanied by a high purity (g2(0)=2.1%), a high photon coherence (Hong-Ou-Mandel visibility of ~97%), maintained over thousands of consecutive emitted photons, and a radiative lifetime of just 50 ps.