Resonant Raman scattering of single molecules under strong cavity coupling and ultrastrong optomechanical coupling in plasmonic resonators: phonon-dressed polaritons

TL;DR

This paper explores how plasmonic dimer cavities enable ultrastrong coupling with single molecules, revealing complex phonon-polariton interactions and spectral features through a rigorous quantum master equation approach.

Contribution

It introduces a comprehensive master equation model for resonant Raman scattering in ultrastrong coupling regimes, including phonon dressing and bath effects, with realistic gold nanocavity parameters.

Findings

Rich spectral resonances due to phonon-modified polaritons

Failure of standard master equations in quantum nonlinear regimes

Identification of bath-induced spectral features

Abstract

Plasmonic dimer cavities can induce extreme electric-field hot spots that allow one to access ultrastrong coupling regimes using Raman-type spectroscopy on single vibrating molecules. Using a generalized master equation, we study resonant Raman scattering in the strong coupling regime of cavity-QED, when also in the vibrational ultrastrong coupling regime, leading to "phonon-dressed polaritons". The master equation rigorously includes spectral baths for the cavity and vibrational degrees of freedom, as well as a pure dephasing bath for the resonant two-level system, which play a significant role. Employing realistic parameters for gold dimer cavity modes, we investigate the emission spectra in several characteristic strong-coupling regimes, leading to extremely rich spectral resonances due to an interplay of phonon-modified polariton states and bath-induced resonances. We also show explicitly the failure of the standard master equation in these quantum nonlinear regimes.