EXCITON-KLO-PHONON QUANTUM KINETICS - EVIDENCE OF MEMORY EFFECTS IN BULK GAAS

Oscillations of the transient four-wave-mixing signal with a period of about 100 fs are observed in bulk GaAs using 14 fs pulses tuned to th e exciton resonance at low temperatures. The measurements are explaine d in terms of the non-Markovian quantum kinetics for electron-hole pai rs due to LO-phonon scattering. it is shown that the observed oscillat ions are evidence for memory effects. The experiments provide a first test of the central ideas of quantum kinetics, in which the effects of quantum coherence and of dissipation are intrinsically connected.