The frequency of an atomic clock may be stabilized against C-field variation by applying a rf magnetic field perpendicular to the C-field to cause a coherent population transfer between Zeeman states that compensates for quadratic frequency shift of transitions of the clock. The cancellation, provided by a feed-forward mechanism, is exact. The invention can be implemented in any atomic clock by including an electrode in the clock generating a magnetic field perpendicular to the C-field, and providing an electronic circuit to send rf signals to the electrode.