Contribution of negative-energy states to the E2−M1 polarizability of optical clocks

The authors theoretically investigate the impact of Dirac negative-energy states on the $E$2 and $M$1 polarizabilities in optical clocks. They demonstrate the importance of negative-energy states for the $M$1 polarizability and resolve the sign inconsistency between the theoretical calculations and experimental measurements in the $E$2-$M$1 polarizability difference of the Sr clock.