Dissipation, coherence, interferences in polaritonic molecular states strongly coupled to plasmons

By confining the cavity mode to a plasmonic nanoparticle, polaritonic states can exist in solution, at room temperature, and in very large quantities. This turns polaritonic structures into functional groups that can be built into, for example, photocatalysts. However, for these excitations to be used in this way, we need to understand their dissipative dynamics in detail. In these systems, more so than in molecule-cavity polaritons, inelastic processes inside the metal, such as e-e and e-ph scattering, strongly modulate the lifetime and coherence of the excitation.
In the first part of the talk, I present a detailed study of the dissipative dynamics of plexcitons from excitation to thermalization. Using two-dimensional electronic spectroscopy, we assign a physical origin (metallic or molecular) to each observed dissipative process, providing a roadmap for improving the materials.
In the second part of the talk, I discuss our approach to the simulation of experiments by combining non-Hermitian Hamiltonians and double-sided Feynman diagrams. The afforded decomposition of both linear and nonlinear signals makes evident the physics above and below the exceptional point, clarifies the connection with Fano interferences, and suggests telltale signatures in third-order spectroscopies.