Coherent interband effects in quantum kinetics

The quantum kinetics of a laser pulse exciting electrons and holes interacting with LO‐phonons is studied in [l] within the generalized Kadanoff‐Baym approximation, but the spectral Green functions are approximated by damped free propagators. After including the Hartree‐Fock coherent terms due to the bare Coulomb interaction, oscillations (“quantum beats”) of the incoherently summed polarization with the LO‐phonon frequency have been found in [2]. Here we include the Coulomb Hartree‐Fock terms as well as the optical pump field selfconsistently for both the spectral and particle functions. This procedure takes the phonon‐assisted transitions and excitonic effects fully into account. Our calculations in three‐dimensional and particularly in two‐dimensional semiconductors show an enhancement of the coherent “quantum beat” effects in the incoherently summed polarization. Further we show that these quantum beats are well resolved in the photon echo signal.