  Advanced quantum information science and technology (QIST) applications place
exacting de- mands on optical components. Quantum waveguide circuits offer a
route to scalable QIST on a chip. Superconducting single-photon detectors
(SSPDs) provide infrared single-photon sensitivity combined with low dark
counts and picosecond timing resolution. In this study we bring these two
technologies together. Using SSPDs we observe a two-photon interference
visibility of 92.3\pm1.0% in a silica-on-silicon waveguide directional coupler
at \lamda = 804 nm-higher than that measured with silicon detectors
(89.9\pm0.3%). We further operated controlled-NOT gate and quantum metrology
circuits with SSPDs. These demonstrations present a clear path to
telecom-wavelength quantum waveguide circuits.
