  We demonstrate scattering of laser light from two InAs quantum dots coupled
to a photonic crystal waveguide, which is achieved by strain-tuning the optical
transitions of the dots into mutual resonance. By performing measurements of
the intensity and photon statistics of transmitted laser light before and after
tuning the dots into resonance, we show that the nonlinearity is enhanced by
collective scattering. In addition to providing a means of manipulating
few-photon optical nonlinearities, our approach establishes new opportunities
for multi-emitter quantum optics in a solid-state platform.
