Isotope Shifts With Ultracold Molecule Clocks

High-precision spectroscopy has long been a cornerstone of experimental physics, enabling discoveries that sharpen our understanding of the physical world. With the development of laser cooling and optical clock technologies, this field has entered a new era of accuracy and control. These techniques, originally perfected for atoms, are now extended to molecules, where additional internal degrees of freedom, such as nuclear vibrations, offer new opportunities. Precision measurements of molecular vibrations provide access to electronic, nuclear, and quantum electrodynamic effects within molecules. In our work, we assemble ultracold diatomic strontium molecules from pairs of laser-cooled Sr isotopes and perform vibrational spectroscopy at clock-level precision. Comparing molecular isotopologues enables accurate measurements of vibrational isotope shifts, allowing tests of molecular quantum electrodynamics and searches for new gravity-like forces acting at nanometer distances. More broadly, our lab develops ultracold molecular gases as platforms for precision measurements and tests of fundamental physics and chemistry.