Superconducting Nanowires for Single-Photon Detection: Progress, Challenges, and Opportunities

Single-photon detectors and nanoscale superconducting devices are two major candidates for realizing quantum technologies. Superconducting-nanowire single-photon detectors (SNSPDs) comprise these two solid-state and optic aspects enabling high-rate (1.3 Gb s⁻¹) quantum key distribution over long distances (>400 km), long-range quantum communication (>1200 km), as well as space communication (239 000 miles). The attractiveness of SNSPDs stems from competitive performance in the four single-photon relevant characteristics at wavelengths ranges from UV to the mid-IR: high detection efficiency, low false-signal rate, low uncertainty in photon time arrival, and fast reset time. However, to date, these characteristics cannot be optimized simultaneously. In this review, the mechanisms that govern these four characteristics are presented, and it is demonstrated how they are affected by material properties and device design as well as by the operating conditions, allowing aware optimization of SNSPDs. Based on the evolution in the existing literature and state of the art, it is proposed how to choose or design the material and device for optimizing SNSPD performance, while possible future opportunities in the SNSPD technology are also highlighted.