Spectroscopy of ⁸⁶Sr₂ for a Molecular Isotope Shift Measurement

We aim to compare a molecular isotope shift measurement to quantum chemistry calculations in order to constrain QED in bound systems and nm-scale Yukawa forces. Previously we demonstrated record clock-level precision for a vibrational transition measurement in ⁸⁸Sr₂, and we plan to perform a similar measurement in other isotopologues. We have created and characterized ultracold, trapped clouds of ⁸⁶Sr₂ molecules, including in the very weakly bound halo state.  The presence of the halo state can enable observation of the interatomic Casimir-Polder interaction. We identified a suitable molecular transition to the 1u excited-state potential and used it to tune the differential polarizability of a clock transition to create a magic-wavelength condition. These results demonstrate a new ultracold molecular system and provide the groundwork for precise molecular isotope-shift spectroscopy.