  We study theoretically the quantum optical properties of hybrid molecules
composed of an individual quantum dot and a metallic nanoparticle. We calculate
the resonance fluorescence of this hybrid system. Its incoherent part, the one
arising from nonlinear quantum processes, results to be enhanced by more than
two orders of magnitude as compared to that in the absence of the metallic
nanoparticle. Scattering spectra at different excitation powers and
nonperturbative calculations of intensity-field correlation functions show that
this system can act as a nonlinear ultra-compact two-photon switch for incident
photons, where the presence (or absence) of a single incident photon field is
sufficient to allow (or prevent) the scattering of subsequent photons. We also
find that a small frequency shift of the incident light field may cause changes
in the intensity field correlation function of orders of magnitude.
