Designing a compact cavity-enhanced source of entangled photons

Quantum repeaters will require sources of entanglement allowing efficient coupling to quantum memories. Here, we address this challenge with a compact, narrowband source design. The entangled pairs are generated via SPDC in two perpendicularly oriented nonlinear crystals in a Fabry-P\'e{}rot cavity. We show that the case of highly non-degenerate wavelengths and type-II phase matching is the most promising candidate for a practical implementation. Using the parameters of an experiment we are currently working on, this design should allow generating entangled photons with a bandwidth of a few MHz.