  Control of nonlinear response of nanostructures via path interference
effects, i.e., Fano resonances, has been studied extensively. In such studies,
a frequency conversion process takes place near a hot spot. Here, we study the
case where the frequency conversion process takes place \textit{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 orders of magnitude enhancement is possible, on top of the
enhancement due to localization effects. That is, this factor multiplies the
enhancement taking place due to the field localization.
