Polariton response in the presence of Brownian dissipation from molecular vibrations

Linear response of molecular polaritons

In this article, we show that the collective light-matter strong coupling regime where N molecular emitters couple to the photon mode of an optical cavity can be mapped to a quantum impurity model where the photon is the impurity that is coupled to a bath of anharmonic transitions. In the thermodynamic limit where N ≫ 1, we argue that the bath can be replaced with an effective harmonic bath, leading to a dramatic simplification of the problem into one of the coupled harmonic oscillators. We derive simple analytical expressions for linear optical spectra (transmission, reflection, and absorption) where the only molecular input required is the molecular linear susceptibility. This formalism is applied to a series of illustrative examples, showing the role of temperature, disorder, vibronic coupling, and optical saturation of the molecular ensemble, explaining that it is useful even when describing an important class of nonlinear optical experiments. For completeness, we provide Appendixes A-C that include a self-contained derivation of the relevant spectroscopic observables for arbitrary anharmonic systems (for both large and small N) within the rotating-wave approximation. While some of the presented results herein have already been reported in the literature, we provide a unified presentation of the results as well as new interpretations that connect powerful concepts in open quantum systems and linear response theory with molecular polaritonics.

Effects of Electron-Vibration Interaction in Polariton Luminescence: Non-Markovian Fano Resonances and Hot Luminescence

We have developed a non-Markovian theory of the polariton luminescence taking the molecular vibrations into account. The calculations were performed in the polariton basis. We have shown that the frequency shift and the polariton spectral line broadening strongly depend on the frequency-dependent exciton contribution to the polariton. In the single-mode microcavity, our non-Markovian theory predicts the Fano resonances in the polariton luminescence and also narrowing of the spectral lines with the increase of the total number of molecules in the case of the intramolecular nature of the low-frequency vibrations. The theory enables us to consider a nonequilibrium (hot) exciton-polariton luminescence similar to the hot luminescence of molecules and crystals. This opens a way for its observation in organic-based nanodevices.