Enhancement of the exciton exchange energy splitting by the confined light field in strained microcavities

Here, we report pump-and-probe studies on uniaxially strained semiconductor microcavities. We observe quantum beats in the differential cavity transmission with periods that decrease with increasing excitation power. The beats are assigned to a coherent superposition of bright excitons which are split due to long-ranged exchange interaction. The dependence on the excitation power indicates an enhancement of the long-range exchange interaction by the confined cavity light field.