  The rate of energy transfer in donor-acceptor systems can be manipulated via
the common interaction with the confined electromagnetic modes of a
micro-cavity. We analyze the competition between the near-field short range
dipole-dipole energy exchange processes and the cavity mediated long-range
interactions in a simplified model consisting of effective two-level quantum
emitters that could be relevant for molecules in experiments under cryogenic
conditions. We find that free-space collective incoherent interactions,
typically associated with sub- and superradiance, can modify the traditional
resonant energy transfer scaling with distance. The same holds true for
cavity-mediated collective incoherent interactions in a weak-coupling but
strong-cooperativity regime. In the strong coupling regime, we elucidate the
effect of pumping into cavity polaritons and analytically identify an optimal
energy flow regime characterized by equal donor/acceptor Hopfield coefficients
in the middle polariton. Finally we quantify the build-up of quantum
correlations in the donor-acceptor system via the two-qubit concurrence as a
measure of entanglement.
