Observation of Collisions between Two Ultracold Ground-State CaF Molecules

We measure inelastic collisions between ultracold CaF molecules by combining two optical tweezers, each containing a single molecule. We observe collisions between Σ 2 CaF molecules in the absolute ground state |X ,v =0 ,N =0 ,F =0 ⟩, and in excited hyperfine and rotational states. In the absolute ground state, we find a two-body loss rate of 7 (4 )×10^-11 cm³/s , which is below, but close to, the predicted universal loss rate.