Quantum theory of nonradiative decay dependent on the coupling strength in a plexcitonic system

Abstract

Revealing the quantum dynamics of plexciton, hybridized states produced by a quantum emitter and localized surface plasmon (LSP) in a strong coupling regime is of importance from fundamental and applied points of view. Photoluminescence (PL) spectrum is recognized for essentially reflecting the interaction between light and matter compared with extinction spectrum and scattering spectrum. However, there are still challenges to realize single-emitter plexciton in PL spectrum because of the unexpected nonradiative decay. In this paper, we develop a full-quantum method to describe the interaction between single emitter and a plasmonic nanocavity. By utilizing our model, we find that there is an optimum for surface-fluorescence enhancement near an intermediate coupling regime instead of a strong coupling regime. Furthermore, we show that strong electric-field enhancement will broaden plexciton’s linewidth covering the Rabi splitting in PL spectrum. The relation between nonradiative decay and coupling strength is given by a quantitative method, and we obtain the revised equation for PL spectrum. By comparing the revised PL spectrum with the scattering spectrum, we find that it is best to find optimal fluorescence splitting in the critical point between the intermediate coupling regime and strong coupling regime. Our method provides a theoretical method for explaining the nonradiative decay depending on coupling strength of a plexcitonic system in the PL spectrum and revealing single-emitter quantum optics.