Abstract

We demonstrate that quantum interference strongly affects the coherent emission from semiconductor quantum wells for multi-subband excitation. This quantum interference manifests itself by a pulse-width-limited decay of the four-wave mixing (FWM) emission as a function of time delay even when the dephasing times of all resonances are much longer than the pulse width. Similar observations have been reported for multisubband excitation of Fano and Lorentzian magnetoexcitons in bulk GaAs¹ and for single-subband excitation of the lowest exciton transition and a broadband continuum.² Theoretical modeling requires to consider many-body Coulomb correlation.^1-3 A microscopic theory for multisubband excitation in low-dimensional semiconductor structures is still missing, although the dynamics in low-dimensional structures with various subbands under ultrabroadband pulse excitation becomes increasingly important. Our results demonstrate that quantum interference effects in multisubband systems are not restricted to the magnetic-field case. This reduces the complexity for the development of a microscopic theory of the nonlinear optical response, which takes into account the Coulomb coupling between the various subbands⁴ and possible screening effects.

© 1998 Optical Society of America