# Emission-frequency separated high quality single-photon sources enabled by phonons

## TL;DR

This paper theoretically shows that phonon-assisted off-resonant excitation of quantum dots can produce high-purity, high-brightness single-photon sources with spectral separation from the laser, outperforming resonant methods.

## Contribution

It introduces a phonon-assisted off-resonant excitation scheme that enhances single-photon purity while maintaining brightness and spectral separation, surpassing resonant excitation techniques.

## Key findings

- Single-photon purity is higher with phonon-assisted off-resonant excitation.
- Brightness remains high despite off-resonant excitation.
- Spectral separation enables high-quality photon emission free from laser background.

## Abstract

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.