Macroscopic quantum electrodynamics approach to multichromophoric excitation energy transfer. II. Polariton-mediated population dynamics in a dimer system

In this study, based on the theory developed in Paper I, we explore the combined effects of molecular fluorescence and excitation energy transfer in a minimal model -- a pair of single-vibration-mode chromophores coupled to surface plasmon polaritons. For the chromophores with zero Huang-Rhys factors and strong couplings to surface plasmon polaritons, we find that the frequencies of Rabi oscillations (the strengths of strong light-matter couplings) are associated with the initial excitation conditions. On the other hand, for the chromophores weakly coupled to surface plasmon polaritons, our numerical calculations together with analytical analysis elaborate on the conditions for the superradiant and subradiant decay behaviors. Moreover, we show that the modified decay rate constants can be explicitly expressed in terms of generalized spectral densities (or dyadic Green's functions), revealing a relationship between photonic environments and the collective effects such as superradiance and subradiance.For the chromophores with non-zero Huang-Rhys factors and strong couplings to surface plasmon polaritons, the effects of molecular vibrations emerge. We demonstrate that the low-frequency vibrational modes do not affect the excited-state population dynamics, while the high-frequency vibrational modes can modify either the period of Rabi oscillation (Franck-Condon Rabi oscillation) or the amplitude of excited-state population. Our study shows that the collective effects, including superradiance and subradiance, can be controlled via dielectric environments and initial excitation conditions, providing new insights to polariton chemistry and the design of quantum optical devices