Quantum decoherence of excited states in self assembled quantum dots.

Here we report the measurements of quantum dephasing times on various excited states of hundreds of individual SAQDs in parallel. Detailed analysis on the results of these measurements led us to three possible dephasing mechanisms each of which plays a dominant role at different range of energy separation between the excited state and the ground state (E_rel). These mechanisms are: (1) LO phonon emission when energy separation of excited states match one LO phonon energy. (2) Hole relaxation through LA phonon emission for excited states with unmatched enrgy separations (3) Auger scattering for higher excited states which are energitically and spatially overlapped with continuum like absorption band. Furthermore we also found that some of the excited states with 15 to 20 meV of E_rel show very long dephasing times (50-80ps). Temperature dependent studies on these states suggested that this long dephasing time is due to reduced phase space for LA phonon emission.