Nuclear-Spin-Resolved Studies of Ultracold Rb + KRb Reaction Complexes

Nuclear spins are often expected to act as spectators during chemical reactions. For instance, studies of KRb + KRb collisions indicate that nuclear spins remain coherent and can be effectively described by a unitary transformation. Introducing a free electronic spin and its associated coupling to the nuclear spin provides a new opportunity to test the robustness of this picture. Here, we investigate hyperfine dynamics in KRb + Rb collisions. We prepare different initial hyperfine states and perform hyperfine-state-sensitive measurements on the product-state population distributions. Our observations suggest that the KRb nuclear spin couples to both the orbital motion and the electronic spin. These results offer a short-range probe into the interactions that are present in the collision complex.