Temperature Dependent Performances of Superconducting Nanowire Single-Photon Detectors in an Ultralow-Temperature Region

We present the performances of a superconducting nanowire single-photon detector (SNSPD) in an ultralow-temperature region from 16 mK to 4 K. The system detection efficiency of the SNSPD showed saturation in the bias-current and temperature dependences, and reached the considerably high value of 15% for 100 Hz dark count rate below 1.4 K at a wavelength of 1550 nm even without an optical cavity structure. We found that the dark count exists even at 16 mK and black body radiation becomes its dominant origin in the low temperatures for fiber-coupled devices.