Can Nanocavities Significantly Enhance Resonance Energy Transfer in a Single Donor-Acceptor Pair?

Long-range resonance energy transfer (RET) and the control of energy transfer on the nanoscale have received considerable attention both experimentally and theoretically during the past few decades. We have investigated the RET between a donor/acceptor pair in the nanocavities based on our previous theory developed in the framework of macroscopic quantum electrodynamics (QED). On the basis of this theory, the enhancements in the RET with respect to the rate in vacuum were evaluated for a Fabry-Pérot cavity. When the displacement vector between the two molecules is aligned with the cavity axis of the Fabry-Pérot cavity, we find that cavity modes give enhancements of less than a factor of 10 due to the interference between contributions from resonant and non-resonant cavity modes. By comparison, when the displacement vector between the two molecules is aligned in a plane perpendicular to the cavity axis, we find that the cavity modes can induce enhancements of more than a factor of 10, and the surface plasmon-polariton modes can induce enhancements of up to a factor of 300. We develop a convenient representation for understanding the effect of the displacement vector between the molecules and of the molecular dipole directions in terms of the H-dimer and J-dimer properties. To further enhance the RET, we propose a square silver cavity that gives a rate enhancement of a factor of 280 under cavity resonance conditions, which provides important insight into developing devices capable of long-range RET.