A second-generation strontium molecular clock for tests of fundamental physics

Recently we demonstrated a Sr₂ molecular lattice clock, based on a transition between vibrational levels in the ground-state potential. This clock is a good testing ground for nanometer-range forces between nuclei. Previously we have characterized the total fractional systematic uncertainty on a vibrational transition in the ⁸⁸Sr₂ isotopologue to <5x10^-14. In the future we plan to measure similar transitions in the other molecular isotopologues assembled with bosonic Sr atoms in order to constrain Yukawa-type forces at the nanometer scale. Here we discuss a next-generation molecular clock apparatus built to address factors currently limiting our precision. We plan to implement a vertical build-up cavity for the lattice, which will increase coherence time by reducing lattice-induced light scattering and molecular collisions. Additionally, a new Sr source will help produce adequate numbers of the lower-natural-abundance isotopes, ⁸⁶Sr and ⁸⁴Sr, for a vibrational isotope shift measurement.