Photon emission through spontaneous parametric downconversion in plasmonic and metamaterial structures

Quantum nonlinear optics provides a robust platform for generating single and entangled photons – critical components of quantum information processing. Typically, the weak nonlinear interactions and high dispersion of homogeneous materials limit nonlinear optical processes for potential on-chip integration. In this work we study use of nanoplasmonic and metamaterial structures for enhancement and control of spontaneous quantum emission through nonlinear parametric downconversion. We develop a theoretical formalism based on eigenmode decomposition accounting for material dispersion, losses and anisotropy. We show that by engineering the optical dispersion in plasmonic waveguides and hyperbolic metamaterials, phase matching, efficient mode mixing, and large density of optical states may be achieved simultaneously to enable enhanced spontaneous quantum photon emission. We study several possible geometries using real material parameters and show that photon emission rates compact nanometer sized structures are comparable to those attainable in bulk crystals.