Superconducting single photon detector: research and applications

During last twenty years, a new generation of superconducting detectors based on hot-electron-phenomena was developed. These sensors have already demonstrated performance that makes them devices-of-choice for many terahertz, infrared and optical applications. The development of compact helium-free cryocoolers together with effective sources of terahertz and infrared radiation greatly expanded the field of application of superconducting detectors including astronomy, medicine, security and quantum communications, and made them friendly in use. To date, due to the growing interest, the market for superconducting devices is gradually expanding, as evidenced by the emergence of small companies engaged in the development, improvement and commercialization of superconducting devices. One such device is the superconducting nanowire single-photon detector (SNSPD or SSPD). SNSPDs combine high detection efficiency, low dark count rate, and high temporal resolution in a single device in visible and near IR range. SNSPDs have been successfully employed for classical and quantum optics applications ranging from optical time domain reflectometry (OTDR), light detection and ranging (LiDAR), space-to-ground communications, quantum dot photonics, quantum key distribution to experiments with indistinguishable and entangled photon pairs and applications in the life sciences. Few years ago, a fully integrated circuit including a single photon source (carbon nanotube), detectors (SNSPDs) and Si3N4 waveguides has already been implemented on a chip. Going beyond such proof-of-principle concepts, the realization of large scale QPICs is expected to have profound impact on science and technology, material engineering, as well as quantum information processing including quantum computing, simulation and metrology. It has recently been shown that the nanosize of the current-carrying strip is not a necessary attribute for single-photon detection. Using a kinetic-equation approach, the dynamics of electrons and phonons in current-carrying superconducting strip with a current close to the depairing current after the absorption of a single photon of the near-infrared or optical range was studied. Second, it has been experimentally demonstrated that single-photon detection is indeed achieved in micrometer-wide NbN bridges biased by a direct current close to the experimental critical current, which is estimated to be at least 50