Mode splitting of a cavity with a high-density birefringence rubidium vapor in the superstrong coupling regime

The mode splitting in a system with Doppler-broadened high-density two-level atoms in the presence of magnetic field inside a relatively long optical cavity is studied in the superstrong coupling regime (atoms-cavity coupling strength g (sqrt N ) is near or larger than the cavity free-spectral range ΔFSR). The effect of a magnetic field applied along the quantization axis is used to break the polarization degeneracy of the cavity and thereby introduce birefringence (or Faraday rotation) into the medium. The cavity modes are further split in the presence of the magnetic field compared with the normal case of the multi-normal-mode splitting of the two-level system near the D2 line of ⁸⁷Rb. The dependence of the mode splitting on the magnetic field and the temperature is studied. The theoretical analysis according to the linear dispersion theory can provide a good explanation.