High-efficiency, low noise UV superconducting nanowire single-photon detectors operating above 4 K

We have demonstrated ∼ 80% detection efficiency of 370 nm photons using superconducting nanowire single-photon detectors (SNSPDs) operating at 4.2 K, with system dark count rates below 1 count/s. Prospects for detecting shorter wavelengths are discussed.