High-resolution ultracold-molecule spectroscopy with possible sensitivity to QED

We describe an optimized route for producing microkelvin ground-state $^{88}$Sr$_2$ molecules in an optical lattice, and an efficient imaging approach based on ultracold fragmentation. This imaging technique yields high-Q molecular spectra. The high-resolution Zeeman spectra uncover very weakly bound rovibrational states with possible sensitivity to QED effects, and challenge the theoretical description of this seemingly simple system.