Coulomb quantum kinetics and optical dephasing on the femtosecond time scale

Quantum kinetic equations with memory are formulated and solved for the femtosecond Coulomb kinetics of an optically excited electron-hole plasma. In a time interval smaller than the inverse plasma frequency screening and energy conservation are still absent. The resulting decay of the optical interband polarization is shown to be nonexponential and is in qualitative agreement with the results of the quasiclassical theory of Gurevich et al.