abstract: We show that in an array of coupled cavities doped with two level systems(atoms or quantum dots), one could exploit photon blockade to achieve a Mott insulator state with polaritons. By varying the detuning of the atomic level spacing and photonic frequency one can proceed from a photon superfluid in a lattice to a polaritonic Mott state. I will also describe how in the Mott regime the system could simulate a XY spin model with the presence and absence of polaritons corresponding to spin up and down and propose a robust scheme of entangling atoms in two separate distant cavities.