Excitons and cavity polaritons for ultracold atoms in an optical lattice

We study the resonant electronic excitation dynamics for ultracold atoms trapped in a deep optical lattice prepared in a Mott-insulator state. Excitons in these artificial crystals are similar to Frenkel excitons in noble atom or molecular crystals. They appear when the atomic excited state linewidth is smaller than the exciton bandwidth generated by dipole-dipole coupling. When the atoms are placed within a cavity the electronic excitations and the quantized cavity mode get coupled. In the collective strong coupling regime excitations form two branches of cavity polaritons with Rabi splitting larger than the atomic and the cavity linewidth. To demonstrate their properties we calculate the transmission, reflection, and absorption spectra for an incident weak probe field, which show resonances at the polariton frequencies