Reducing noise in single-photon-level frequency conversion.

We demonstrate low-noise and efficient frequency conversion by sum-frequency mixing in a periodically poled LiNbO(3) (PPLN) waveguide. Using a 1556 nm pump, 1302 nm photons are efficiently converted to 709 nm photons. We obtain 70% conversion efficiency in the PPLN waveguide and >50% external conversion efficiency with 600 noise counts per second at peak conversion with continuous-wave pumping. We simultaneously achieve low noise and high conversion efficiency by careful spectral filtering. We discuss the impact of low-noise frequency translation on single-photon upconversion detection and quantum information applications.