Magnetic dipole transition

A transition driven by an oscillating magnetic field through $H^{\prime }=-\mathbf{\mu }\cdot \mathbf{B}$. The rank-one magnetic operator preserves parity and allows changes in total angular momentum of zero or one, excluding zero-to-zero. Its spherical components select changes in the angular momentum component of $0,\pm 1$. Hyperfine clock states can therefore couple even when each has zero first-order static magnetic moment.