Fig. 2: Key building blocks of the platform.

a, Schematics of photon source, filter network, interferometer and detector. b, Measured joint spectral intensity of an interferometrically coupled resonator photon source, indicating a spectral purity of 99.5% (Supplementary Information). c, Response of our pump filter network. We shade the pump, signal and herald frequency bands and show the measured herald (orange) and signal (blue) filter spectrum, characterized with on-chip SNSPDs. d, Measured response of a Mach–Zehnder interferometer to heralded single-photon illumination on a fully integrated platform. The extinction ratio at the transmission port is >50 dB. The asymmetry in the Mach–Zehnder interferometer response is an artefact of a non-constant step size, which is finer around one feature only. There is no marked variation in performance across a circuit or among different circuits. e, Measured on-chip detection efficiency as a function of detector bias current (I_B) normalized by the detector switching current (I_SW) and the detector count rate (blue) and dark count rate (orange) per second (inset) (Supplementary Information).