Heralded single-photon source
= Heralded single-photon source
Detection of one member of a pair conditions the other mode towards a one-photon state. Imperfect collection reduces heralding efficiency; unresolved spectral correlations can leave a mixed state, and multiple pairs can contaminate the heralded output. Filtering can improve purity while reducing brightness. Heralding is conditional preparation, not deterministic conversion of every pump pulse.