  We report on the generation of an indistinguishable heralded single-photon
state, using highly nondegenerate spontaneous parametric downconversion (SPDC).
Spectrally factorable photon pairs can be generated by incorporating a
broadband pump pulse and a group-velocity matching (GVM) condition in a
periodically-poled potassium titanyl phosphate (PPKTP) crystal. The heralding
photon is in the near IR, close to the peak detection efficiency of
off-the-shelf Si single-photon detectors; meanwhile, the heralded photon is in
the telecom L-band where fiber losses are at a minimum. We observe spectral
factorability of the SPDC source and consequently high purity (90%) of the
produced heralded single photons by several different techniques. Because this
source can also realize a high heralding efficiency (> 90%), it would be
suitable for time-multiplexing techniques, enabling a pseudo-deterministic
single-photon source, a critical resource for optical quantum information and
communication technology.
