  The modified radiative and non-radiative states due to the weak coupling of
an emitter with other resonant objects (Purcell effect), can be recast as a
quantum interference of the paths of the photon that define the classical
scattering and absorption by the object. When the coupling is stronger,
additional paths representing the (Rabi oscillations or) possible re-absorption
of the photon from the excited object, by the emitter at ground-state, have to
be included in the quantum interference. The effect of these additional Rabi
paths of the photon on the radiative states and the efficiency of spontaneous
emission, can be approximated using a simple one-loop correction to the
weak-coupling approximation. This effect is especially evident in the anomalous
enhancements of emission due to extremely small non-scattering (or fully
absorbing) metal nanoparticles less than 10 nm in dimensions. Extending these
corrections to a collective model of spontaneous emission that includes
multiple emitters and such very small metal nanoparticles coupled to each
other, the large contribution of Rabi paths to radiative decay in such bulk
materials is elucidated.
