  Control of nonlinear response of nanostructures via path interference
effects, i.e. Fano resonances, has been studied extensively. In such materials,
a frequency conversion process which takes place near a hot spot has been
considered. Here, we study a different case. The frequency conversion process
takes place along the body of a nonlinear crystal. Metal nanoparticle-quantum
emitter dimers control the down-conversion process, taking place throughout the
crystal body, via introducing interfering conversion paths. Dimers behave as
interaction centers. We show that a 2 order of magnitude enhancement is
possible, beyond an enhancement due to localization effects. This factor
multiplies the enhancement taking place due to the field localization.
