Evidence of six-particle Coulomb correlations in six-wave-mixing signals from a semiconductor quantum well

Six-cave-mixing signals from a ZnSe quantum well ark analyzed experimentally and with a microscopic density-matrix description using the dynamics-controlled-truncation scheme. For each physically distinct combination of polarizations of the exciting pulses, the spectrum of six-wave-mixing emission is measured as a function of time delay. The experimental results are compared with calculations performed at different levels of approximation. Although the leading order contributions to six-wave-mixing signals are of fifth order in the laser field, we show that there are significant signal components that are due to at least chi ((7)) processes. The sensitivity of six-wave-mixing signals to high-order Coulomb correlations is demonstrated. Six-point density matrices are found to be indispensable for the interpretation of our experiments, while some details seem to indicate the involvement of even higher-order correlation functions. Furthermore, we find a remarkable dynamical decoupling of spectral signatures and the delay-time behavior after excitation with linearly polarized pulses.