Optical dephasing of coherent intersubband transitions in a quasi-two-dimensional electron gas

We present a microscopic many-particle theory for the dephasing of coherent intersubband excitations in semiconductor quantum wells including carrier-carrier and carrier-phonon scattering and light propagation effects. The contributions of many-particle processes are nonadditive and thus cannot be treated separately. It is shown that due to nondiagonal correlation contributions, scattering rates alone cannot be taken as a measure for the dephasing of the intersubband polarization. Surprisingly, radiative damping is found to be important even at moderate carrier densities. Calculated absorption spectra are in excellent agreement with experiments on a high-quality sample.