Fully Saturated Hydrocarbons as Hosts of Optical Cycling Centers

Designing closed, laser-induced optical cycling transitions
in
trapped atoms or molecules is useful for quantum information processing,
precision measurement, and quantum sensing. Larger molecules that
feature such closed transitions are particularly desirable, as the
increased degrees of freedom present new structures for optical control
and enhanced measurements. The search for molecules with robust optical
cycling centers is a challenge which requires design principles beyond
trial-and-error. Two such principles are proposed for the particular
M–O–R framework, where M is an alkaline earth metal
radical, and R is a ligand: (1) Large, saturated hydrocarbons can
serve as ligands, R, due to a substantial HOMO–LUMO gap that
encloses the cycling transition, so long as the R group is rigid.
(2) Electron-withdrawing groups, via induction, can enhance Franck–Condon
factors (FCFs) of the optical cycling transition, as long as they
do not disturb the locally linear structure in the M–O–R
motif. With these tools in mind, larger molecules can be trapped and
used as optical cycling centers, sometimes with higher FCFs than smaller
molecules.