Coherent control of exciton polaritons in a semiconductor microcavity

We report on the dynamics of resonantly excited lower branch polariton stat es in a semiconductor quantum microcavity. We show that both the spin orien tation and the density of polaritons can be coherently manipulated. The mea surements of the optical dephasing Lime T-2 and the decay time T-1 of the r adiant states asa function of the cavity detuning and the lattice temperatu re give further insights into the relaxation mechanisms of cavity polariton s. [S0163-1829(99)51104-1].