Temporal and photon number resolution of superconducting nanowire single-photon detectors

Single-photon detectors based on superconducting nanowires (SNSPDs) are promising technologies with good comprehensive performance, especially their excellent temporal resolution for applications in quantum precision measurements and time-varying ultimate detection. The response time of an SNSPD can be characterized by aspects of hotspot thermal relaxation and electrical relaxation, which are also responsible for the time jitter of the SNSPD. The factors affecting the temporal resolution of an SNSPD, the underlying physical mechanism, the intrinsic limit, and possible optimization methods are reviewed. The poor energy resolution and lack of photon number resolution for conventional SNSPDs can be overcome by using high-impedance readouts, novel device structures, characterization methods and, most importantly, SNSPD arrays, which can simultaneously further improve the temporal resolution. The study of the temporal and photon number resolution of SNSPDs helps reveal the underlying physics and is valuable for their new application in various practical engineering areas.