Solid-state single-photon emitters

Single-photon emitters play an important role in many leading quantum technologies. There is still no 'ideal' on-demand single photon emitter, but a plethora of promising material systems have been developed, and several have transitioned from proof-of concept to engineering efforts with steadily improving performance. Here, we review recent progress in the race towards true single-photon emitters required for a range of quantum information processing applications. We focus on solid-state systems including quantum dots, defects in solids, two-dimensional hosts and carbon nanotubes, as these are well positioned to benefit from recent breakthroughs in nanofabrication and materials growth techniques. We consider the main challenges and key advantages of each platform, with a focus on scalable on-chip integration and fabrication of identical sources on photonic circuits.