Sensitivity and gigahertz counting performance of NbN superconducting single-photon detectors

We have measured the quantum efficiency (QE), GHz counting rate, jitter, and noise-equivalent power (NEP) of nanostructured NbN superconducting single-photon detectors (SSPDs) in the visible to infrared radiation range. Our 3.5-nm-thick and 100- to 200-nm-wide meander-type devices (total area 10x10 mum(2)), operating at 4.2 K, exhibit an experimental QE of up to 20% in the visible range and similar to10% at 1.3 to 1.55 mum wavelength and are potentially sensitive up to midinfrared (similar to10 mum) radiation. The SSPD counting rate was measured to be above 2 GHz with jitter <18 ps, independent of the wavelength. The devices' NEP varies from similar to10(-17) W/Hz(1/2) for 1.55 mum photons to similar to10(-20)W/Hz(1/2) for visible radiation. Lowering the SSPD operating temperature to 2.3 K significantly enhanced its performance, by increasing the QE to similar to20% and lowering the NEP level to similar to3x10(-22) W/Hz(1/2), both measured at 1.26 mum wavelength. (C) 2004 American Institute of Physics.