On the prospects of optical cycling in diatomic cations: Effects of transition metals, spin-orbit couplings, and multiple bonds

Abstract

Molecules with optical cycling centers (OCCs) are highly desirable in the context of fundamental studies as well as applications (e.g., quantum computing) because they can be effectively cooled to very low temperatures by repeated absorption and emission (hence, cycling). Charged species offer additional advantages for experimental control and manipulation. We present a systematic computational study of a series of diatomic radical-cations made of a d-block metal and a p-block ligand, that are isoelectronic (in their valence shell) to the successfully laser-cooled neutral molecules. Using high-level electronic structure methods, we characterize state and transition properties of low-lying electronic states and compute Franck-Condon factors. The computed branching ratios and radiative lifetimes reveal that the electronic transitions analogous to those successfully used in the laser cooling of neutral molecules are less than optimal in the cations. We propose alternative transitions suitable for optical cycling and highlight trends that could assist future designs of OCCs in charged or neutral molecules.

Multivalent optical cycling centers in polyatomic molecules

“…We note that the new design principles described here could possibly be extended to molecular ions, which have powerful advantages for precision measurements [102,216,217] and quantum science [218,219], but are challenging systems for incorporating optical cycling [24,220,221]. The limitations of narrow linewidth transitions present in the types of molecules discussed here would be less relevant in ion traps, which do not rely on photon cycling to trap.…”