A collaborative experiment with the Ong group (Princeton) shows that at low temperature (T < 150 mK), the transition between Chern states in a quantum anomalous Hall insulator occurs via sudden macroscopic magnetization reversal events. These events are detected as sudden discrete jumps in the anomalous Hall resistance and their variation with temperature and chemical potential suggest a quantum tunneling out of a false vacuum [Liu et al., Science Advances, 2016].