  Integration of photon pairs nanosources is a major challenge for quantum
technology. In this context, we develop a formalism for the investigation of
Spontaneous Parametric Down Conversion in hybrid structures that combine
plasmonic resonances and intrinsic nonlinearity. Using quantum and numerical
approaches together, we quantitatively evaluate photon pair correlation
measurements for realistic experimental configurations. Hybrid structures
embedding a small nanocystal allow for a $10^{3}$ fold increase in pair
production compared to the same nanocrystal alone and a photon pair production
efficiency close to the best source to date.
