  Efficient synchronization of single photons that are compatible with
narrowband atomic transitions is an outstanding challenge, which could prove
essential for photonic quantum information processing. Here we report on the
synchronization of independently-generated single photons using a
room-temperature atomic quantum memory. The photon source and the memory are
interconnected by fibers and employ the same ladder-level atomic scheme. We
store and retrieve the heralded single photons with end-to-end efficiency of
$\eta_\text{e2e}=25\%$ and final anti-bunching of $g^{(2)}_\text{h}=0.023$. Our
synchronization process results in over tenfold increase in the photon-pair
coincidence rate, reaching a rate of more than $1000$ detected synchronized
photon pairs per second. The indistinguishability of the synchronized photons
is verified by a Hong-Ou-Mandel interference measurement.
