He-3-Xe-129 Comagnetometery using Rb-87 Detection and Decoupling

We describe a He-3-Xe-129 comagnetometer using Rb-87 atoms for noble-gas spin polarization and detection. We use a train of Rb-87 pi pulses and sigma(+)/sigma(-) optical pumping to realize a finite-field Rb magnetometer with suppression of spin-exchange relaxation. We suppress frequency shifts from polarized Rb by measuring the He-3 and Xe-129 spin precession frequencies in the dark, while applying pi pulses along two directions to depolarize Rb atoms. The plane of the pi pulses is rotated to suppress the Bloch-Siegert shifts for the nuclear spins. We measure the ratio of He-3 to Xe-129 spin precession frequencies with sufficient absolute accuracy to resolve Earth’s rotation without changing the orientation of the comagnetometer. A frequency resolution of 7 nHz is achieved after integration for 8 h without evidence of significant drift

Femtotesla Nearly-Quantum-Noise-Limited Pulsed Gradiometer at Earth-Scale Fields

We describe a magnetic gradiometer that operates at finite fields and uses an intense pulsed laser to polarize a 87Rb atomic ensemble and a compact vertical-cavity surface-emitting laser probe laser to detect paramagnetic Faraday rotation in a single multipass cell. We report differential magnetic sensitivity of 14 fT/Hz1/2, corresponding to gradiometer sensitivity of 70 fT/cm/√Hz with a 0.2 cm baseline, over a broad dynamic range, including Earth’s field magnitude and a common-mode rejection ratio higher than 104. We also observe a nearly quantum-noise-limited behavior of the gradiometer by comparing the experimental standard deviation of the estimated frequency difference against the Cramér-Rao lower bound in the presence of white photon shot-noise, atomic spin noise, and diffusion