Nondegenerate two-photon absorption from single quantum dot biexcitons

Summary form only given. Two excitons can bind to form a biexciton through the Coulomb interaction. In a quantum dot (QD), the binding is greatly enhanced due to 3D confinement. Previous work has focused on luminescence from biexciton-to-exciton transitions. We report the first coherent nonlinear optical spectra of a biexcitonic system. Such types of studies provide vital information on the exciton/biexciton lifetime as well as the optically-induced quantum coherence and its decay. The realization of coherent optical devices based on QD systems, such as proposed for quantum logic operations, relies critically on these measurements.