  Photons have proven to be excellent carriers of quantum information, and play
essential roles in numerous quantum information processing (QIP) applications.
In particular, heralded single- photon sources via spontaneous parametric-down
conversion (SPDC) have been a key technology for demonstrating small-scale QIP,
yet their low generation efficiency is a critical limitation for further
scaling up optical QIP technology. In order to efficiently overcome the
probabilistic nature of SPDC, here we demonstrate time multiplexing for up to
30 time slots of a periodically pumped heralded single-photon source, using a
switchable low-loss optical storage cavity. We observe a maximum single-photon
probability of 38.6% in periodic output time windows, corresponding to 6 times
enhancement over a non-multiplexed source, but with no increase in the
contribution of unwanted multi-photon events. Combining this time-multiplexing
technique with a heralded source producing pure single-photon states should
enable larger scale optical QIP systems than ever realized.
