Two Approaches for Nuclear Spin Co-magnetometry

Abstract

Nuclear spin comagnetometers are precision probes well-suited for tests of fundamental physics and inertial rotation sensing, thanks to their inherent suppression of magnetic field noise. This thesis discusses developments in two approaches commonly employed for nuclear spin comagnetometry. The first approach is termed quantization-axis comparison, where the ensemble-averaged spin orientation of alkali-metal electron spins and noble-gas nuclear spins are compared to determine if any anomalous fields that couple to the spins differently from magnetic fields are acting on one or both spin species. The second approach is termed clock-comparison, where the free-precession frequencies of two nuclear spin species are compared to reveal frequency shifts of non-magnetic origin. The implementations of both approaches in this thesis utilize the highly sensitive spin-exchange-relaxation free (SERF) magnetometer to probe spin dynamics. The two approaches complement each other, in the sense that the alkali-metal-noble-gas comagnetometer performs better at short time scales, i.e. within a few minutes, but does not have good long-term stability primarily due to drifts in optical alignment, while the free-precession comagnetometer accommodates days-long interrogation time, but the sampling rate that optimizes sensitivity is on the order of 1/T2 ~0.001 Hz, which is determined by the T2 coherence time of the noble-gas nuclear spins. This thesis investigates a pulsed optical pumping approach for the alkali-metal-noble-gas comagnetometer, which reduces sensitivity to certain types of optical misalignments. The pulsed mode is capable of simultaneous measurement of couplings along two orthogonal axes in the plane perpendicular to the pump beam, while its continuously pumped predecessors are sensitive to a single axis. For the free-precession comagnetometer, a 3He and 21Ne system is optimized, taking advantage of the long coherence times and weak self-interactions among the spins. Sub-nHz sensitivity over one day is attained, which corresponds to 10-24 eV energy sensitivity, rendering it the most sensitive comagnetometer of this type.