Coherent spin dynamics of exciton-polaritons in diluted magnetic microcavities

Kerr rotation induced by femtosecond pulses in a CdMnTe quantum well embedded in a microcavity is studied under an in-plane magnetic field. Due to giant Zeeman splitting in the diluted magnetic quantum well, in this system we deal with two spin splitted exiton states coupled to the cavity mode. For such a microcavity operating in the strong coupling regime, the polariton spin beats in the time-resolved Kerr rotation signal can be expected at three distinct frequencies. Two of them are observed in our experiments, in a excellent agreement with the theoretical calculation in the framework of the polariton spin density matrix, which accounts for the finite lifetimes of exciton and photon states.