Coherent Dynamics Of An Asymmetric Double Quantum Well

Coherent optical effects coming from two excited levels in an engineered asymmetric double quantum well have been detected with duration of picoseconds.1This short decoherence time is related with the dephasing time. Although dephasing is mainly due to electron–electron scattering and LO phonons in polar semiconductor provide the dominant inelastic scattering mechanism, a study of the elastic scattering with phonons during the coherent stage is also needed to understand the coherent electron dynamics. In this work is presented a microscopic study of the elastic scattering rates due to electron–LO-phonon interaction, which are obtained for each of the three conduction subbands on a tailored double asymmetric quantum well by using the imaginary part of the polaron self-energy within a many-body formalism. Both absorption and emission rates are calculated. The dephasing times for different electronic states in a given heterostructure can be very different, depending on the material, geometry, temperature, carrier density, etc. As an important geometric parameter is chosen the barrier width, which tunes the energy differences between the two upper levels or tunneling times. Electron density effect is studied through screening. Two limits are presented — unscreened and static screening. It is found that after an ultrashort pulse the absorption and emission scattering rates in each level are very different from the scattering rates in equilibrium and that screening effects can be used as coherent control mechanism.