Restoring Bloch's Theorem for Cavity Exciton Polaron-Polaritons

Abstract: We introduce a symmetry-informed representation for hybrid photon--exciton--phonon quantum electrodynamics Hamiltonians to restore Bloch's theorem. The interchange of momenta between fermions and bosons breaks crystalline excitons' translational symmetry under strong coupling. Restoring said symmetry, we efficiently compute experimentally accessible observables without introducing approximations to the Hamiltonian, enabling investigations that elucidate material properties in strong coupling with applications enhancing coherent transport and unlocking symmetry-forbidden matter transitions.