Colour centres in diamond as practical single-photon sources

The paper describes a "turn-key" single-photon source based on nitrogen-vacancy (N-V) colour centre photoluminescence inside dispersed diamond nanocrystals. The authors have used the emitted single photons to realize a wave-particle delayed-choice experiment based on a Mach-Zehnder interferometer. The diamond-based single-photon source is also to open-air quantum key distribution (QKD).