  Narrowband single photons that couple well to atomic ensembles could prove
essential for future quantum networks, but the efficient generation of such
photons remains an outstanding challenge. We realize a spatially-multiplexed
heralded source of single photons that are inherently compatible with the
commonly employed D2 line of rubidium. Our source is based on four-wave mixing
in hot rubidium vapor, requiring no laser cooling or optical cavities, and
generates single photons with high rate and low noise. We use Hong-Ou-Mandel
interference to verify the indistinguishability of the photons generated in two
different (multiplexed) channels. We further demonstrate a five-fold tunability
of the photons' temporal width. The experimental results are well reproduced by
a theoretical model.
