  Scalable photonic quantum technologies require on-demand single-photon
sources with simultaneously high levels of purity, indistinguishability, and
efficiency. These key features, however, have only been demonstrated separately
in previous experiments. Here, by s-shell pulsed resonant excitation of a
Purcell-enhanced quantum dot-micropillar system, we deterministically generate
resonance fluorescence single photons which, at pi pulse excitation, have an
extraction efficiency of 66%, single-photon purity of 99.1%, and photon
indistinguishability of 98.5%. Such a single-photon source for the first time
combines the features of high efficiency and near-perfect levels of purity and
indistinguishabilty, and thus open the way to multi-photon experiments with
semiconductor quantum dots.
