Nondegenerate coherent control of polariton modes in a quantum-well semiconductor microcavity

We demonstrate nondegenerate coherent control of the cavity-polariton modes of a quantum-well semiconductor microcavity. Coherent excitation and de-ex citation of one normal mode using a pair of phase-locked optical pulses giv es rise to a nonlinear response on the other normal mode due to the nonline arity of the exciton transition underlying the normal modes. The cavity enh ancement of the excitonic nonlinearity gives rise to a large signal; modula ting the relative phase of the excitation pulses between zero and pi produc es a differential reflectivity (Delta R/R) of up to 15%. Coherent control i s used to measure the polariton dephasing time as a function of density. Ex citation induced dephasing is shown to be the factor limiting the degree of coherent control.