Confinement of molecules within a cavity leads to a strong coupling between light and matter degrees of freedom, merging the two into a quasiparticle known as a polariton. Theoretical treatments of molecular polaritons generally utilize either exact diagonalization of the interacting molecule-cavity system Hamiltonian or perturbation theory to analyze intracavity light-matter interactions. The former is constrained in its capacity to account for the open nature of the molecular cavity system, while the treatment of strong interactions within perturbation theory represents a weakness of the latter. Here, we introduce a pseudoparticle nonequilibrium Green's function (PP-NEGF) formulation for molecular polariton spectroscopy. This formulation addresses the limitations of currently available approaches by accounting for all intrasystem interactions exactly and treating system-bath couplings within diagrammatic expansion and extends a recent NEGF-based formulation for nonlinear optical spectroscopy to strongly interacting molecular systems. Theoretical derivations are demonstrated through numerical simulations, where we examine the impact of strong light-matter interaction on fluxes and multidimensional optical spectroscopy of cavity polaritons.
Li et al. (Thu,) studied this question.