Intrinsic quantum efficiency and electro-thermal model of a superconducting nanowire single-photon detector

Superconducting single-photon detectors from thin niobium nitride nanostrips exhibit a cut-off of the wavelength-independent quantum efficiency along with a moderate energy resolution in the near-infrared spectral range. Before the cut-off, the intrinsic quantum efficiency of the detector reaches 30% of the ultimate value, which is physically limited to the absorbance of the detector structure. The intrinsic quantum efficiency is most likely controlled by non-homogeneities of the niobium nitride films. We have developed an electro-thermal model of the detector response that allowed us to optimize the SQUID-based readout and to achieve, in the temperature range from 1 to 6 K, the photon count rate 3 107 s-1 and a dark count rate less than 10-4 s-1.