Diatomic Ions: New Candidates For Laser Cooling*

Trapped ions form Coulomb crystals, where couplings between phonons and ions' internal degrees of freedom are extensively used in quantum technologies. In contrast to other cold and ultracold species, diatomic ions support not only electric charge but also permanent electric dipole moment, and as molecules, they host rotational and vibrational degrees of freedom. This wealth of quantum states appeals for applications in physics and quantum information.

The prerequisite for advancing the field is an access to cold samples of diatomic ions. We present a systematic, computational study aimed at finding the most promising candidates for laser cooling. With the most advanced methods of computational chemistry (that include spin-orbit couplings), we localize electronic transitions in the visible range, characterized by diagonal Franck-Condon factors. This work not only marks the best diatomic ions for laser cooling, but also offers a guide for a rational design of their properties.

[1] M. V. Ivanov et al.: Phys. Chem. Chem. Phys. 22, 17075 (2020)