Investigation of Non Resonant Dot - Cavity Coupling in Two Dimensional Photonic Crystal Nanocavities

We study the optical emission from single semiconductor quantum dots coupled to the optical modes of photonic crystal nanocavities. For dots that are both spectrally and spatially coupled, auto-correlation measurements reveal efficient single photon generation, with a drastically reduced lifetime due to the Purcell-effect. However, the multi-photon emission probability is enhanced compared to the same QD transition when it is detuned from the cavity mode by controlled $N_2$-deposition. This indicates the presence of an emission background that is shown to be related to the dot using photon cross-correlation spectroscopy. Photon temporal correlations persist even for large spectral detunings beyond $\Delta\lambda\sim-10 nm$, excluding the intrinsic QD continuum and phonon mediated processes as being responsible for the cavity mode emission background. We propose a mechanism based on photon induced shake up processes in the charged quantum dots, enhanced by the optical cavity.