We have studied the spin dynamics in self-organized InAs/GaAs quantum dots by time-resolved photoluminescence performed under strictly resonant excitation. At low temperature, we observe strictly no decay of both the linear and the circular luminescence polarization. This demonstrates that the carrier spins are totally frozen on the exciton lifetime scale.

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We demonstrate that the optical orientation of excitons can be coherently controlled and directly observed in a resonant time resolved photoluminescence experiment. The optical dephasing time of excitons, their longitudinal and transverse spin relaxation times, and their radiative lifetime, are measured with strictly the same experimental conditions. The measurements rely on the linear response of the crystal. [S0031-9007(97)04222-1]