Stationary coherence in semiconductor microcavities

We have investigated the coherent dynamics of a semiconductor microcavity b y means of interferometric correlation measurements with fs resolution. We bring clear evidence of the resolution of a homogeneous polariton line in a n inhomogeneously broadened exciton system. Moreover, we observe an unexpec ted stationary coherence up to 8 ps for the lower polariton branch close to resonance. Linear dispersion theory including an exciton asymmetric inhomo geneous broadening accounts for the coherent dynamics but does not predict the stationary coherence. [S0163-1829(99)51616-0].