In the field-free case, all of these energy levels for each J value are degenerate, but in the presence of a circularly polarized light field, the Autler-Townes effect, (AC Stark shift or light shift), lifts this degeneracy. The extent and direction of this lifted degeneracy is dependent on the polarization of the light. It is this polarization dependence that is leveraged to apply a spatially-dependent slowing force to the atom.