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 2Σ 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.