Noise-assisted purification of a single-photon source

Scalable quantum networks and photonic quantum technologies require single-photon sources with extremely high purity. In resonantly driven two-level systems typically employed in realizing such sources, photon purity is generally limited by multiphoton emission and residual laser scattering, traditionally treated as independent noise sources. Here, we reveal that residual laser scatter can be coherently engineered to interfere destructively with unwanted multiphoton emission, dramatically enhancing single-photon purity. Through theoretical modeling, we identify optimal excitation conditions where phase-sensitive interference harnesses noise to boost emission purity by several orders of magnitude without sacrificing brightness. These results introduce a new design paradigm for quantum light sources, where scattered light becomes a powerful resource for advancing scalable, high-purity photon generation in integrated photonic platforms.