  Semiconductor quantum dots are considered to be the leading venue for
fabricating on-demand sources of single photons. However, the generation of
long-lived dark excitons imposes significant limits on the efficiency of these
sources. We demonstrate a technique that optically pumps the dark exciton
population and converts it to a bright exciton population, using intermediate
excited biexciton states. We show experimentally that our method considerably
reduces the DE population while doubling the triggered bright exciton emission,
approaching thereby near-unit fidelity of quantum dot depletion.
