Origin of the asymmetric light emission from molecular exciton–polaritons

We apply the theory of open-quantum systems to describe light emission from coherently driven molecular polaritons. Based on the microscopic Hamiltonian that commonly describes the pure dephasing of isolated molecules, we show that under strong-coupling conditions dephasing leads to a transfer of energy between the constituted polariton branches $|\pm\rangle$. When the polariton dephasing is properly accounted for, the transition from the upper to the lower polariton branch is favored and leads to a dominant population of the lower polariton branch under coherent pumping conditions. As a result, the inelastic light emission originates mainly from the lower polariton state regardless of the pumping laser frequency thus producing an asymmetric emission of light. Furthermore, we show that, when several molecules are considered, inter-molecular coupling breaks the symmetry of the system, making the originally dark polaritons to effectively interact with light. This effect is revealed in the fluorescence spectrum as new emission peaks.