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 10×10μm2), operating at 4.2K, exhibit an experimental QE of up to 20% in the visible range and ∼10% at 1.3 to 1.55μm wavelength and are potentially sensitive up to midinfrared (∼10μm) radiation. The SSPD counting rate was measured to be above 2GHz with jitter <18ps, independent of the wavelength. The devices’ NEP varies from ∼10−17W∕Hz1∕2 for 1.55μm photons to ∼10−20W∕Hz1∕2 for visible radiation. Lowering the SSPD operating temperature to 2.3K significantly enhanced its performance, by increasing the QE to ∼20% and lowering the NEP level to ∼3×10−22W∕Hz1∕2, both measured at 1.26μm wavelength.

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We demonstrate a bright, bandwidth-tunable, quasi-phase-matched single-waveguide source generating photon pairs near 900 nm and 1300 nm. Two-photon coincidence spectra are measured at a range of operating temperatures of a periodically-poled KTiOPO(4) (PPKTP) waveguide, which supports both type-0 and type-II spontaneous parametric down-conversion. We map out relative contributions of two-photon to one-photon fluorescence for a range of operating parameters. Such a versatile device is highly promising for future chip-scale quantum information processing.

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