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Résumé:

We discuss the decoherence dynamics in a single semiconductor quantum dot and analyze two dephasing mech- anisms. In the ¯rst part of the review, we examine the intrinsic source of dephasing provided by the coupling to acoustic phonons. We show that the non-perturbative reaction of the lattice to the interband optical transition results in a composite optical spectrum with a central zero-phonon line and lateral side-bands. In fact, these acoustic phonon side-bands completely dominate the quantum dot optical response at room temperature. In the second part of the paper, we focus on the extrinsic dephasing mechanism of spectral di®usion that determines the quantum dot decoherence at low temperatures. We interpret the variations of both width and shape of the zero- phonon line as due to the °uctuating electrostatic environment. In particular, we demonstrate the existence of a motional narrowing regime in the limit of low incident power or low temperature, thus revealing an unconventional phenomenology compared to nuclear magnetic resonance.