Cavity electromagnetically induced transparency and optical switching with ion Coulomb crystals

We report on the first observation of cavity EIT with ion Coulomb crystals (40Ca⁺ ions) enclosed in a moderately high-finesse linear cavity, in a novel configuration where both the probe and the control field are injected into the cavity. The weak probe field (single photon level), and the more intense control field originate from the same laser and are both tuned to the same atomic transition (3d²D_3/2-4p²P_1/2), but with opposite circular polarizations to address separate Zeeman sub-states of the 3d²D_3/2 level.