Characterizing a Metropolitan Fiber Link with Heralded Single Photons from an Electronic-Photonic Chip

We characterize single photon transmission through a ~ 48 km underground fiber link. Using an integrated source, we measure delay variations in the timing correlations between the photon-pairs of 40 ps over 90 minutes, compared to 200 ps in a 50 km spool kept in the laboratory, showing the suitability of buried fiber for quantum networks.