Development of co-located 129Xe and 131Xe nuclear spin masers with external feedback scheme

Abstract We report on the operation of co-located 129 Xe and 131 Xe nuclear spin masers with an external feedback scheme, and discuss the use of 131 Xe as a comagnetometer in measurements of the 129 Xe spin precession frequency. By applying a correction based on the observed change in the 131 Xe frequency, the frequency instability due to magnetic field and cell temperature drifts are eliminated by two orders of magnitude. The frequency precision of 6.2 μHz is obtained for a 10 4 s averaging time, suggesting the possibility of future improvement to ≈ 1 nHz by improving the signal-to-noise ratio of the observation.