  We study dynamics of the interaction between two weak light beams mediated by
a strongly coupled quantum dot-photonic crystal cavity system. First, we
perform all optical switching of a weak continuous-wave signal with a pulsed
control beam, and then perform switching between two pulsed beams (40ps pulses)
at the single photon level. Our results show that the quantum dot-nanocavity
system creates strong, controllable interactions at the single photon level.
