Progress toward an isotope shift measurement with a strontium molecular lattice clock

Molecular vibrations in Sr₂ are of interest for a molecular clock thanks to exceedingly long clock-state lifetimes and transition frequencies in the THz frequency range where few frequency standards currently exist. We plan to utilize a novel technique to constrain gravity-like fifth forces by comparing molecular isotope shift measurements to state-of-the-art quantum chemistry calculations. This relies on the existence of several bosonic Sr isotopes and on a ground-state molecular energy structure that is feasible, though challenging, to describe theoretically. Previously, we have extensively characterized the creation, spectroscopy, and clock systematic effects at the hertz level with ⁸⁸Sr₂. Here, we describe progress toward measurements with ⁸⁶Sr₂ and other molecular isotopologues.