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

Incoherent pumping in quantum dots 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 ∝ 1/γ(S), due to the slow spin relaxation rate γ(S) in quantum dots. The existence of the dark path is shown to impose a limitation on the single photon emission process, especially in nanocavities which exhibit a large exciton-cavity coupling and a Purcell enhancement for fast quantum telecommunications.