Atomic magnetic resonance based current source

A current of 1 A has been stabilized by locking the magnetic resonance frequency of Cs atoms placed at the center of a solenoid. Two auxiliary windings are used to obtain at the center of the solenoid a field uniformity better than 0.5 ppm in a 2 cm radius sphere, in agreement with the calculations. The variations of the external field and the effect of temperature changes are compensated for by two auxiliary feedback systems using a flux gate magnetometer and an adjustment of the locking frequency, respectively. The current fluctuation, including the noise of the current measuring system is 0.1 ppm and the current drift for 6 h is less than 0.2 ppm.