SERF Comagnetometer Based on Self-Differential Mode

The spin-exchange relaxation-free (SERF) comagnetometer is significant in exploring fundamental physics and high-precision inertial sensing. Traditional continuous measurement based on steady atomic spin polarization, however, limits the suppression of long-term drifts, which is pivotal for inertial navigation and the search for new physics beyond the standard model. In this article, we propose a SERF comagnetometer based on self-differential measurement mode using reverse-modulated atomic spin polarization for signal enhancement and noise suppression. We analyze the dynamic evolutions of alkali electron spin and noble-gas nuclear spin under the pulsed left-hand (OR left rotating) and right-hand (OR right rotating) circularly polarized pumping scheme. In order to ensure that the comagnetometer operates in a self-compensation regime, we reverse the electron spin while keeping the nuclear spin polarization stable by optimizing the modulation period and duty cycle. Working in the self-differential, the response of the comagnetometer to the inertial input is improved by 2.95 dB, and the low-frequency common mode at 0.1–2 Hz is suppressed by about 6.53 dB. The sensitivity is improved by 2.7 times to $3.1\times 10^{-6\circ }$ /s/ $\text{Hz}^{\mathrm {1/2}}$ at 1 Hz compared with the traditional continuous measurement mode. This method can also be applied to precision measurements based on atomic spin, such as nuclear magnetic resonance (NMR) gyroscopes and optically pumped atomic magnetometers.