  Using electric dipoles to describe light-matter interactions between two
entities is a conventional approximation in physics, chemistry, and material
sciences. However, the lack of material structures makes the approximation
inadequate when the size of an entity is comparable to the spatial extent of
electromagnetic fields or the distance between two entities. In this study, we
develop a unified theory of radiative and non-radiative resonance energy
transfer based on transition current density in a theoretical framework of
macroscopic quantum electrodynamics. The proposed theory allows us to describe
polariton-assisted resonance energy transfer between two entities with
arbitrary material structures in spatially dependent vacuum electric fields. To
demonstrate the generality of the proposed theory, we rigorously prove that our
theory can cover the main results of the transition density cube method and the
plasmon-coupled resonance energy transfer. We believe that this study opens a
promising direction for exploring light-matter interactions beyond the scope of
electric dipoles and provides new insights into material physics.
