Dissipative preparation of the exciton and biexciton in self-assembled quantum dots on picosecond time scales

Pulsed resonant fluorescence is used to probe ultrafast phonon-assisted exciton and biexciton preparation in individual self-assembled InGaAs quantum dots. By driving the system using large area (>= 10 pi) near resonant optical pulses, we experimentally demonstrate how phonon-mediated dissipation within the manifold of dressed excitonic states can be used to prepare the neutral excitonwith a fidelity >= 70%. By comparing the phonon-assisted preparationwith resonant Rabi oscillations we showthat the phonon-mediated process provides the higher-fidelity preparation for large pulse areas and is less sensitive to pulse area variations. Moreover, by detuning the laser with respect to the exciton transition, we map out the spectral density for exciton coupling to the bulk LA-phonon continuum. Similar phonon-mediated processes are shown to facilitate direct biexciton preparation via two-photon biexciton absorption, with fidelities >80%. Our results are found to be in very good quantitative agreement with simulations that model the quantum dot-phonon bath interactions with Bloch-Redfield theory.