Superradiant and Dark Exciton States in an Optical Lattice within a Cavity

We study ultracold atoms in a finite size one-dimensional optical lattice prepared in the Mott insulator phase and commonly coupled to a single cavity mode. Due to resonance dipole-dipole interactions among the atoms, electronic excitations delocalize and form {\it excitons}. These exciton modes are divided into two groups: antisymmetric modes which decouple from the cavity mode forming {\it dark states}, and symmetric modes significantly coupled to the cavity mode called {\it bright states}. In typical setups the lowest and most symmetric exciton is coupled to the cavity photons much stronger than the other bright states and dominates the optical properties response of the atoms ({\it superradiant state}). In the strong coupling regime this superradiant state is coherently mixed with the cavity photon to form a doublet of polariton states with the Rabi splitting.