Coherent coupling of ion Coulomb crystals to different transverse modes of an optical cavity

The authors report on CQED experiments where solid state features of ion Coulomb crystals are exploited for detailed studies of the coherent collective coupling of ions of such crystals to different transverse modes of the cavity. By using extremely prolate ion Coulomb crystals oriented along the cavity axis with a radial extension of only a few tens of microns, the spatial profiles of different cavity modes are mapped out by measuring the effective coherent coupling as the crystal is moved radially across the cavity modes. From the resulting profile of the coupling strength, the cavity mode transverse profile can be reconstructed.