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. [1] P. Michler et al., A quantum dot single-photon turnstile device, Science 290, 2282 (2000) [2] A. Berthelot et al., Unconventional motional narrowing in the optical spectrum of a semiconductor quantum dot, Nature Physics 2, 759 (2006) [3] A. Muller et al., Resonance fluorescence from a coherently driven semiconductor quantum dot in a cavity, PRL 99, 187402 (2007) [4] R. Melet et al., Resonant excitonic emission of a single quantum dot in the Rabi regime, PRB 78, 073301 (2008) [5] S. Ates et al., Post-selected indistinguishable photons from the resonance fluorescence of a single quantum dot in a microcavity, PRL 103, 167402 (2009) O02B6 48

We report on original nonlinear spectral hole-burning experiments in ensembles of single-wall carbon nanotubes. We have measured the temperature dependence of the excitonic homogeneous linewidth from 5 K up to room temperature. We show that the phonon-induced broadening in the weak coupling regime predominantly consists in pure dephasing. We present theoretical calculations of the exciton scattering rate due to phonon absorption within a one-dimensional framework for both excitons and phonons. We obtain a fair agreement with our experimental data and we discuss the specific properties of the exciton-phonon coupling in single-wall carbon nanotubes.

We report on original nonlinear spectral hole-burning experiments in single wall carbon nanotubes that bring evidence of pure dephasing induced by exciton-exciton scattering. We show that the collision-induced broadening in carbon nanotubes is controlled by exciton-exciton scattering as for Wannier excitons in inorganic semiconductors, while the population relaxation is driven by exciton-exciton annihilation as for Frenkel excitons in organic materials. We demonstrate that this singular behavior originates from the intrinsic one-dimensionality of excitons in carbon nanotubes, which display unique hybrid features of organic and inorganic systems.

We present nonlinear optical spectroscopy in GaN/AlN quantum dots that allow for the measurements of the homogeneous broadening of the intraband transition at 1.55 µm. We find that the population relaxation is driven by Auger processes, which play on the contrary a minor role in the decoherence dynamics.

The one-dimensionality of carriers in single-wall carbon nanotubes results in strong Coulomb interactions. Besides the non-perturbative binding of an electron-hole pair into an exciton, several time-resolved experiments have shown evidence for efficient exciton-exciton interactions. These studies have revealed that the exciton recombination is driven by an exciton-exciton annihilation mechanism. In fact such an Auger process is known to play a key role in the population relaxation of Frenkel excitons in organic materials, and especially J-aggregates and conjugated polymers. Here we show that the similarity with organic molecules breaks down for the dephasing induced by exciton-exciton interactions. We have studied the exciton dephasing by means of the non-linear optical technique of spectral-hole burning. We show that the collision broadening is surprisingly not limited by exciton-exciton Auger annihilation. We demonstrate that the coherence relaxation is determined by quasi-elastic exciton-exciton scattering within the fundamental excitonic band. This process is typical of Wannier excitons in inorganic semiconductors, while exciton annihilation is usually observed for Frenkel excitons in organic compounds. Our results reveal the unique non-linear properties of carbon nanotubes in between inorganic and organic materials.

The one-dimensionality of carriers in single-wall carbon nanotubes results in strong Coulomb interactions. Besides the non-perturbative binding of an electron-hole pair into an exciton, several time-resolved experiments have shown evidence for efficient exciton-exciton interactions. These studies have revealed that the exciton recombination is driven by an exciton-exciton annihilation mechanism. In fact such an Auger process is known to play a key role in the population relaxation of Frenkel excitons in organic materials, and especially J-aggregates and conjugated polymers. Here we show that the similarity with organic molecules breaks down for the dephasing induced by exciton-exciton interactions. We have studied the exciton dephasing by means of the non-linear optical technique of spectral-hole burning. We show that the collision broadening is surprisingly not limited by exciton-exciton Auger annihilation. We demonstrate that the coherence relaxation is determined by quasi-elastic exciton-exciton scattering within the fundamental excitonic band. This process is typical of Wannier excitons in inorganic semiconductors, while exciton annihilation is usually observed for Frenkel excitons in organic compounds. Our results reveal the unique non-linear properties of carbon nanotubes in between inorganic and organic materials.