  A strong optical nonlinearity arises when coherent light is scattered by a
semiconductor quantumdot (QD) coupled to a nano-photonic waveguide. We exploit
the Fano effect in such a waveguide to control the phase of the quantum
interference underpinning the nonlinearity, experimentally demonstrating a
tunable quantum optical filter which converts a coherent input state into
either a bunched, or antibunched non-classical output state. We show
theoretically that the generation of non-classical light is predicated on the
formation of a two-photon bound state due to the interaction of the input
coherent state with the QD. Our model demonstrates that the tunable photon
statistics arise from the dependence of the sign of two-photon interference
(either constructive or destructive) on the detuning of the input relative to
the Fano resonance.
