Résumé
Single photon emission is one of the most striking optical properties of semiconductor quantum dots (QDs), and the corresponding photon anti-bunching effect was observed by photoluminescence experiments in single QDs under non-resonant excitation [1]. In this configuration, the residual excitation of the QD environment that acts as a fluctuating reservoir for spectral diffusion [2] reduces the coherence time and prevents from the realization of single photons sources with high degree of indistinguishability. Therefore, strictly resonant excitation of the fundamental interband transition [3,4,5] is essential to reduce the dephasing processes and get high-performance single photon sources. In this paper, we report on the resonant Rayleigh scattering (RRS) of the exciton in single InAs/GaAs QDs embedded in a planar microcavity [3]. Strikingly, the most frequent case (98%) corresponds to the absence of resonance in the RRS spectrum, resulting in QDs non-coupled to light. We show that resonant fluorescence of the exciton is restored for all the QDs when an additional non-resonant laser is applied at extremely weak power ranges (few nWs). A clear photon anti-bunching under strictly resonant excitation proves that the optically gated RRS spectrum is dominated by resonant fluorescence of the exciton. A complete study will be presented such as the switching dynamics of the RRS and its power dependence with the resonant and non-resonant lasers. The phenomenon is interpreted within a simple model where the exciton resonant fluorescence is quenched by Coulomb blockade after tunneling of a hole in the QD from a structural deep level. The additional non-resonant laser suppresses Coulomb blockade by switching back the QD into a neutral state. We conclude that the optical response of the QD remains affected by its environment even in case of coherent resonant pumping. An optical control of the QD environment is essential to bring the QD from a "dark" to a "bright" state under strictly resonant excitation. References [1] P. Michler et al., Science 290, 2282 (2000) [2] A. Berthelot et al., Nature Physics 2, 759 (2006) [3] A. Muller et al., PRL 99, 187402 (2007) [4] R. Melet et al., PRB 78, 073301 (2008) [5] S. Ates et al., PRL 103, 167402 (2009)