that the Zeeman shifts approach $\Gamma$, the cooling laser is tuned away from resonance and the scattering rate decreases.

If the polarization is a combination of $\pi$ and $\sigma^+$ (this can be achieved by an elliptically polarized beam traveling at an angle to the QA), the $\Lambda$ system $|1\rangle \leftrightarrow |8\rangle \leftrightarrow |2\rangle$ is formed, but it is not closed, as the $|1\rangle \leftrightarrow |7\rangle$ transition is also driven. Hence the contrast of the corresponding CPT resonance is less than unity, i.e., the scattering rate decays rapidly, but not to 0 \[dash-dotted (green) curve in Fig. \[fig:g-states\]\].

If the cooling laser is linearly polarized ($\pi$, $\sigma$, or combination thereof in the QA frame), there is no dark state among the ground levels. The slow decay of the dotted (blue) curve in Fig. \[fig:g-states\] is due to dark states among the metastable sublevels, which are considered in Sec. \[sec:m-states\]. In the following, we therefore only consider a linearly polarized cooling beam.

Ground-metastable-level dark states
-----------------------------------

The ground-metastable-level dark states are CPT superposition states of $|g\rangle$ and $|m\rangle$ sublevels. As the two legs of the $\Lambda$ systems are driven by separate lasers, the CPT resonances can be detected by tuning one of 