  Photonic integrated circuits (PICs) have emerged as a scalable platform for
complex quantum technologies using photonic and atomic systems. A central goal
has been to integrate photon-resolving detectors to reduce optical losses,
latency, and wiring complexity associated with off-chip detectors.
Superconducting nanowire single-photon detectors (SNSPDs) are particularly
attractive because of high detection efficiency, sub-50-ps timing jitter,
nanosecond-scale reset time, and sensitivity from the visible to the
mid-infrared spectrum. However, while single SNSPDs have been incorporated into
individual waveguides, the system efficiency of multiple SNSPDs in one photonic
circuit has been limited below 0.2% due to low device yield. Here we introduce
a micrometer-scale flip-chip process that enables scalable integration of
SNSPDs on a range of PICs. Ten low-jitter detectors were integrated on one PIC
with 100% device yield. With an average system efficiency beyond 10% for
multiple SNSPDs on one PIC, we demonstrate high-fidelity on-chip photon
correlation measurements of non-classical light.
