Fluctuations and dark count rates in superconducting NbN single‐photon detectors

We measured the temperature- and current-dependence of dark count rates of a superconducting single-photon detector. The detector's key element is a 84 nm wide meander strip line fabricated from an 5 nm thick NbN film. Due to its reduced dimensions various types of fluctuations cancause temporal and localizied transitions into a resistive state leading to dark count events. Adopting a recent refinement of the hot-spot model we achieve a satisfying description of the experimental dark count rates taking into account fluctuations of the Cooper-pair density and current-assisted unbinding of vortex-antivortex pairs.