  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 ($\geq10\pi$) 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 exciton with a fidelity $\geq 70\%$. By comparing the phonon-assisted
preparation with resonant Rabi oscillations we show that 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.
