Superconducting single-photon ultrathin NbN film detector

Superconducting single-photon ultrathin NbN film detectors are studied. The development of manufacturing technology of detectors and the reduction of their operating temperature down to 2 K resulted in a considerable increase in their quantum efficiency, which reached in the visible region (at 0.56 mu m) 30 % - 40 %, i.e., achieved the limit determined by the absorption coefficient of the film. The quantum efficiency exponentially decreases with increasing wavelength, being equal to similar to 20% at 1.55 mu m and similar to 0.02% at 5 mu m. For the dark count rate of similar to 10(-4) s(-1), the experimental equivalent noise power was 1.5 x 10(-20) W Hz(-1/2); it can be decreased in the future down to the record low value of 5 x 10(-21) W Hz(-1/2). The time resolution of the detector is 30 ps.