Stochastic Metholodgy Shows Molecular Interactions Protect 2D Polaritons

We introduce stochastic techniques that enable the simulations of polaritons resulting from placing giant 2D molecular aggregate crystals with $10^8$ interacting excitonic dyes in realistic multi-mode cavities. We show that the intermolecular coupling protects the formation of polariton states in the face of strong molecular disorder due to persistent delocalization of the dark molecular states. This demonstrates the nontrivial role of internal aggregate Hamiltonian in polariton properties, and the new computational method opens horizons for stochastic simulations of related systems.