Ramsey-Scheme ³He-²¹Ne Comagnetometer with Finite-Field SERF ⁸⁷Rb Magnetometer Readout

Noble-gas comagnetometer systems take advantage of the subtraction of common systematic effects by comparing multiple polarized nuclear spin species with long spin coherence time, and demonstrated high sensitivity to spin-energy splittings originating from various spin interactions, such as inertial rotation and new physics beyond the standard model like EDM and axion dark matter. We develop a Ramsey-scheme ³He-²¹Ne comagnetometer with finite-field SERF ⁸⁷Rb magnetometer readout based on a former ³He-¹²⁹Xe-⁸⁷Rb system [PRL, 120, 033401 (2018)]. ²¹Ne is favored over ¹²⁹Xe for its much longer spin coherence time, and smaller frequency shifts due to both Fermi-contact interaction with ⁸⁷Rb and contact dipolar interation with ³He. A Ramsey pulse sequence is implemented to limit signal amplitude within the ⁸⁷Rb magnetometer's dynamic range without compromising on signal-to-noise ratio(SNR), and to improve the statistical sensitivity of frequency measurements. After the nuclear spins are polarized by spin-exchange with Rb vapor optically pumped parallel to an applied bias field, we turn off lasers, actively depolarize Rb, and apply the π/2 pulse - free evolution- π/2 pulse Ramsey sequence to both nuclear spin species in the dark. Pump and probe lasers are turned back on afterwards to read residual precession signals at the nuclear spins' respective Larmor frequencies, whose amplitudes are proportional to the difference between applied pulse frequencies and Larmor frequencies in the bias field. With our setup's current SNR and spin coherence times we project a sub-100 pHz frequency resolution after integration for 24 hours for a sequence optimized with Cramér–Rao lower bound calculations.