In this review, we address the extrinsic dephasing mechanism of spectral diffusion that dominates the decoherence in semiconductor quantum dots at cryogenic temperature. We discuss the limits of random telegraph and Gaussian stochastic noises, and we describe the general effect of motional narrowing in the context of spectral noise. We emphasize the unconventional phenomenology of motional narrowing in standard semiconductor quantum dots at low incident power and temperature, that makes the quantum dot emission line a sensitive probe of the extrinsic reservoir fluctuation dynamics. We further show that the text book phenomenology of motional narrowing in nuclear magnetic resonance is recovered in quantum dots embedded in field-effect heterostructure. In that case, the electrical control of the mesoscopic environment of the quantum dot leads to conventional motional narrowing where the motion consists in carrier tunneling out of the defects around the quantum dot

We present a general theoretical description of the extrinsic dephasing mechanism of spectral diffusion that dominates the decoherence dynamics in semiconductor quantum dots at low temperature. We discuss the limits of random telegraph and Gaussian stochastic noises and show that the combination of both approaches in the framework of the pre-Gaussian noise theory allows a quantitative interpretation of high-resolution experiments in single semiconductor quantum dots. We emphasize the generality and the versatility of our model where the inclusion of asymmetric jump processes appears as an essential extension for the understanding of semiconductor quantum dot physics.

We present homogeneous line width measurements of the intraband transition at 1.55 mu m in GaN/AlN quantum dots by means of nonlinear spectral hole-burning experiments. The square-root dependence of the differential transmission signal with the incident pump power reveals the importance of electron-electron scattering in the population relaxation dynamics. We find on the contrary that this scattering process plays a minor role in the coherence relaxation dynamics since the homogeneous linewidth of 15 meV at 5 K does not depend on the incident pump power. This suggests the predominance of other dephasing mechanisms such as spectral diffusion, and temperature-dependent measurements support this hypothesis. (C) 2010 American Institute of Physics. [doi:10.1063/1.3476340]

We present a review of coherence properties of interband and intraband optical transitions in self assembled InAs/GaAs quantun dots. Indeed, recent experimental and theoretical investigations of the optical transitions in both spectral domains have allowed a better understanding of the different phenomena that affects the interaction of confined carriers with light. These studies point out the many different ways the electron-phonon interactions play a role on the optical response of quantum dots. They also stress the primary role of the close environment on the coherence characteristics of quantum dots. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3130926]

We report on environmental effects on the optical properties of single-wall carbon nanotubes in a gelatin-based composite material designed to foster their photoluminescence. We show that the dielectric screening of excitons due to the surrounding medium is responsible for a sizeable shift of the luminescence lines, which hardly depends on the tube geometry. In contrast, the temperature dependence from 4 to 300 K of the luminescence is clearly chirality dependent; the first and second excitonic lines shift in opposite directions with a magnitude that can be related quantitatively to a strain-induced modification of the electronic structure due to an expansivity mismatch between the nanotube and the matrix.

We demonstrate the control with a dc-voltage of the environment-induced decoherence in a semiconductor quantum dot embedded in a gated ¯eld-e®ect device. The electrical control of the spectral di®usion dynamics governing the quantum dot decoherence induces various e®ects, and in particular a narrowing of the quantum dot emission spectrum on increasing the electric ¯eld applied to the structure. We develop a model in the framework of the pre-Gaussian noise theory that provides a quantitative interpretation of our data as a function of gate voltage. The standard phenomenology of motional narrowing described in nuclear magnetic resonance is successfully reached by hastening the carrier escape from the traps around the quantum dot through tunnelling under reverse bias voltage. Our study paves the way to a protection of zero-dimensional electronic states from outside coupling through a voltage-controlled motional narrowing e®ect.

The ultrafast electron dynamics subsequent to a hundred femtosecond photo-excitation is monitored in a few nanometer thick Au/Co/Au film by means of time-resolved transient spectroscopy. We show that the insertion of the thin Co layer in the Au film leads to a drastic modification of the scattering rates of the different thermalization regimes. The electron-electron interactions are dominated by the mobile sp-electrons scattering on the heavy d-electrons, which concomitantly enhances the electron-phonon interactions by up to a factor of 5. In the framework of ultrafast magnetization dynamics, this study provides important data on the electronic processes underlying the spin dynamics in a sample typically designed for magneto-optical applications.