Ultrafast superconducting single-photon detector

The state-of-the-art of the NbN nanowire superconducting single-photon detector technology (SSPD) is presented. The SSPDs exhibit excellent performance at 2 K temperature: 30% quantum efficiency from visible to infrared, negligible dark count rate, single-photon sensitivity up to 5.6 mu m. The recent achievements in the development of GHz counting rate devices with photon-number resolving capability is presented.