  To realize a quantum network based on quantum entanglement swapping, bright
and completely autonomous sources are essentially required. Here, we
experimentally demonstrate Hong-Ou-Mandel (HOM) quantum interference between
two independent bright photon pairs generated via the spontaneous four-wave
mixing in Doppler-broadened ladder-type 87Rb atoms. Bright autonomous heralded
single photons are operated in a continuous-wave (CW) mode with no
synchronization or supplemental filters. The four-fold photon coincidence
counts per hour correspond to 5000 events for a temporal range of 10 ns, one
order higher than those of previously reported for autonomous single photons.
We observe an HOM dip with 83% visibility with the two autonomous heralded
single photons for an effective measurement time of 900 s. The achievement of
the HOM interference between the two bright autonomous photon-pair sources has
made an important step towards a practical scalable quantum network.
