We demonstrate theoretically that the single-photon purity of photons emitted from a quantum dot exciton prepared by phonon-assisted off-resonant excitation can be significantly higher in a wide range of parameters than that obtained by resonant preparation for otherwise identical conditions. Despite the off-resonant excitation the brightness stays on a high level. These surprising findings exploit that the phonon-assisted preparation is a two-step process where phonons first lead to a relaxation between laser-dressed states while high exciton occupations are reached only with a delay to the laser pulse maximum by adiabatically undressing the dot states. Due to this delay, possible subsequent processes, in particular multi-photon excitations, appear at a time when the laser pulse is almost gone. The resulting suppression of reexcitation processes increases the single-photon purity. Due to the spectral separation of the signal photons from the laser frequencies this enables the emission of high quality single photons not disturbed by a laser background while taking advantage of the robustness of the phonon assisted scheme.
@article{arxiv.1902.06132,
title = {Emission-frequency separated high quality single-photon sources enabled by phonons},
author = {Michael Cosacchi and Florian Ungar and Moritz Cygorek and Alexei Vagov and Vollrath Martin Axt},
journal= {arXiv preprint arXiv:1902.06132},
year = {2019}
}