  We experimentally investigate the dynamic nonlinear response of a single
quantum dot (QD) strongly coupled to a photonic crystal cavity-waveguide
structure. The temporal response is measured by pump-probe excitation where a
control pulse propagating through the waveguide is used to create an optical
Stark shift on the QD, resulting in a large modification of the cavity
reflectivity. This optically induced cavity reflectivity modification switches
the propagation direction of a detuned signal pulse. Using this device we
demonstrate all-optical switching with only 14 attojoules of control pulse
energy. The response time of the switch is measured to be up to 8.4 GHz, which
is primarily limited by the cavity-QD interaction strength.
