Zeeman coherence in single quantum dots

Using coherent nonlinear laser spectroscopy, we show spectral features that indicate contributions from an optically induced nonradiative quantum cohe rence between the two excitonic states of the Zeeman doublet in a single ga llium arsenide quantum dot. The decay rate of this coherence is comparable to the radiative coherence decay rate of the individual excitonic states. T he experiments are explained using a theory based on a simple model taking into consideration the exciton-exciton Coulomb interaction. (C) 2001 Elsevi er Science Ltd. All rights reserved.