Abstract: The normal modes in a nonperturbatively coupled quantum-well semiconductor microcavity are linear superpositions of the QW exciton and cavity mode when the QW exciton transition is resonant with the cavity mode. When the lower normal mode is excited by a phase-locked pair of optical pulses, the nonlinear response of a probe pulse tuned to the upper mode is controlled. Thus the normal modes are coupled in their nonlinear optical response due to the nonlinearity of the exciton underlying the two normal modes. The cavity enhancement of the excitonic nonlinearity gives rise to a large signal; modulating the relative phase of the excitation pulses produces a differential reflectivity of up to 10%. Besides the coherent control of normal modes which is explainable with in the frame of semiclassical models, we observe a purely quantum mechanical phenomenon in our system. The quantum correlations between the field and carrier density lead to intraband coherences which live much longer than the interband dephasing time.!22
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