Impact of the dark path on quantum dot single photon emitters in small cavities

TL;DR

This paper investigates how the dark excitation path in quantum dots affects single photon emission in small cavities, revealing limitations on photon purity due to spin relaxation effects.

Contribution

It demonstrates that dark-pumping pathways increase two-photon emission probability, constraining single photon sources in nanocavities with strong exciton-cavity coupling.

Findings

Dark path enhances two-photon emission probability.

Dark path limits single photon purity in nanocavities.

Spin relaxation rate influences emission characteristics.

Abstract

Incoherent pumping in quantum dots (QDs) can create a biexciton state through two paths: via the formation of bright or dark exciton states. The latter, dark-pumping, path is shown to enhance the probability of two-photon simultaneous emission, and hence increase $g^{(2)}(0)$ by a factor $\propto 1/\gamma_S$, due to the slow spin relaxation rate $\gamma_S$ in QDs. The existence of the dark path is shown to impose a limitation on the single photon (SP) emission process, especially in nanocavities which exhibit a large exciton-cavity coupling and a Purcell enhancement for fast quantum telecommunications.