Strong plasmon-molecule coupling at the nanoscale revealed by first-principles modeling

Strong light-matter interactions in both the single-emitter and collective strong coupling regimes attract significant interest due to emerging applications in quantum optics as well as opportunities for modifying material-related properties. Exploration of these phenomena is theoretically challenging, as polaritons exist at the intersection between quantum optics, solid state physics, and quantum chemistry. In this presentation, we shed light on nanoscale polaritons in small strongly-coupled plasmon-molecule systems by using time-dependent density-functional theory (TDDFT) [1]. By analyzing the electron-hole transitions involved in the excitation process, we dissect the symmetric and antisymmetric polaritonic modes caused by strong coupling between plasmon and molecular excitation, resulting in Rabi oscillations in time domain. Our results indicate that cavity quantum electrodynamics description holds down to resonators of a few cubic nanometers in size. In a broader perspective, first-principles methods enable parameter-free in-depth studies of polaritonic systems for emerging applications.

[1] T. P. Rossi, T. Shegai, P. Erhart, and T. J. Antosiewicz, Nat. Commun. 10, 3336 (2019).