  Quantum entangled photons provide a sensitive probe of many-body interactions
and offer an unique experimental portal for quantifying many-body correlations
in a material system. In this paper, we present a theoretical demonstration of
how photon-photon entanglement can be generated via interactions between
coupled qubits. Here we develop a model for the scattering of an entangled pair
of photons from a molecular dimer. We develop a diagrammatic theory for the
scattering matrix and show that one can correlate the von Neumann entropy of
the outgoing bi-photon wave function to exciton exchange and repulsion
interactions. We conclude by discussing possible experimental scenarios for
realizing these ideas.
