Reduction of the magnetic sensitivity of an atomic clock against the non-uniformity and variations of the C-field

The frequency of an atomic clock may be stabilized against C-field variations by applying weak magnetic pulses tuned to the Larmor frequency. The small signal produced by these pulses is a Ramsey spectrum of the Zeeman transitions which, when added to the microwave Ramsey signal, may be adjusted to compensate exactly for the quadratic frequency shift of clock transition at a given value of the C-field. The cancellation is provided by a feed-forward mechanism which modifies the error signal without the need to adjust the C-field. This can be implemented in most atomic clocks by generating the required audio-frequency pulses on wires producing a magnetic field perpendicular to the C-field.