Dephasing of intersublevel polarizations in InAs/GaAs self-assembled quantum dots

We have performed time-integrated degenerate four-wave mixing experiments in InAs/GaAs self-assembled quantum dots. The quantum dots are excited in resonance with an intersublevel transition between the valence states of the dots. The dephasing time T 2 is deduced from the time dependence of the photon echo amplitude as a function of the delay between the two incident pulses. At low temperature, a dephasing time T 2 of 15 ps is measured for a resonant excitation at 7.4 μm wavelength. This dephasing corresponds to an homogeneous broadening of the intersublevel transition of 87 μeV. The polarization decay time is much longer than the one observed for resonant intersubband excitations in quantum wells. The dephasing time of the intersublevel polarization exhibits only a weak temperature dependence, indicating that the dephasing is not dominated by phonon-assisted scattering mechanisms.