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arXiv:2509.13486

A $^{3}$He-$^{21}$Ne Ramsey Comagnetometer with sub-nHz frequency resolution

Shaobo Zhang, Wang, Jingyao, George Sun, Johannes van de Wetering, Michael V. Romalis

Published Sep 16, 2025• 0 citations
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Abstract

Nuclear spin comagnetometers offer exceptional precision in measurements of spin energy levels and exhibit long-term stability, making them powerful tools for probing spin-dependent physics beyond the standard model as well as for inertial rotation sensing. We describe a new ^{3}He-^{21}Ne Ramsey comagnetometer operating with an in situ ^{87}Rb magnetometer for initialization and sensing of nuclear spins. During free precession of nuclear spins we turn off all lasers and introduce a microwave field to suppress back action from Rb atoms. We demonstrate that scalar and dipolar interactions between nuclear spins can be eliminated via control of the polarized sample geometry. These improvements result in a bias-free measurement with a frequency sensitivity of 0.6 nHz after six hours of integration.

DOI
10.48550/arxiv.2509.13486

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A 3^{3}3He-21^{21}21Ne Ramsey Comagnetometer with sub-nHz frequency resolution
Nuclear spin comagnetometers offer exceptional precision in measurements of spin energy levels and exhibit long-term stability, making them powerful tools for probing spin-dependent physics beyond the standard model as well as for inertial rotation sensing. We describe a new ^{3}He-^{21}Ne Ramsey comagnetometer operating with an in situ ^{87}Rb magnetometer for initialization and sensing of nuclear spins. During free precession of nuclear spins we turn off all lasers and introduce a microwave field to suppress back action from Rb atoms. We demonstrate that scalar and dipolar interactions between nuclear spins can be eliminated via control of the polarized sample geometry. These improvements result in a bias-free measurement with a frequency sensitivity of 0.6 nHz after six hours of integration.
We describe a ^{3}He-^{129}Xe comagnetometer using ^{87}Rb atoms for noble-gas spin polarization and detection. We use a train of ^{87}Rb π pulses and σ^{+}/σ^{-} 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 ^{3}He and ^{129}Xe spin precession frequencies in the dark, while applying π pulses along two directions to depolarize Rb atoms. The plane of the π pulses is rotated to suppress the Bloch-Siegert shifts for the nuclear spins. We measure the ratio of ^{3}He to ^{129}Xe 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.
We describe a 3 He- 129 Xe comagnetometer using 87 Rb atoms for noble-gas spin polarization and detection.We use a train of 87 Rb π pulses and σ þ =σ -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 3 He and 129 Xe spin precession frequencies in the dark, while applying π pulses along two directions to depolarize Rb atoms.The plane of the π pulses is rotated to suppress the Bloch-Siegert shifts for the nuclear spins.We measure the ratio of 3 He to 129 Xe 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.
Atomic spin sensors are essential for beyond-the-standard-model exploration, biomagnetic measurement, and quantum navigation. While the traditional DC mode spin-exchange relaxation-free (SERF) comagnetometer achieves ultrahigh sensitivity, further improvements require suppressing technical noise and surpassing standard quantum limit. In this work, we develop a K-Rb- 21 Ne SERF atomic comagnetometer that dynamically polarizes the electron and nuclear spins, shielding signals from direct interference by pump light. We establish a three-phase evolutionary model for hybrid spin ensemble dynamics, yielding a complete analytical solution, and analyze the responses to various spin perturbations. Additionally, we achieve an average 39% suppression of the polarization noise and identify the key factors that limit sensitivity improvements. The dynamically polarized comagnetometer exhibits effective suppression of technical noise and holds the potential to overcome quantum noise limit while offering promising applications in exploring new physics and precise magnetic field measurements.
A spin-exchange relaxation-free comagnetometer is a promising high-precision gyroscope as its inertial measurement sensitivity can rival that of existing technologies. The magnetic field error is one of the main factors that limits the long-term stability of the comagnetometer. The steady-state response and frequency response models of a K-Rb-21Ne comagnetometer are modified by considering the spin-exchange rate between the electron spins and the nuclear spins. The modified models are used to redefine the bias magnetic sensitivity of the K-Rb-21Ne comagnetometer and the suppression method of low-frequency magnetic field error is proposed. We demonstrate the magnetic drift suppression method proposed in the article by optimizing the cell temperature and pump laser power density. This study is helpful to improve the rotation measurement performance of the K-Rb-21Ne comagnetometer.
Atomic spin sensors are essential for beyond-the-standard-model exploration, biomagnetic measurement, and quantum navigation. While the traditional DC mode spin-exchange relaxation-free (SERF) comagnetometer achieves ultrahigh sensitivity, further improvements require suppressing technical noise and surpassing standard quantum limit. In this work, we develop a K-Rb-21^{21}21Ne SERF atomic comagnetometer that dynamically polarizes the electron and nuclear spins, shielding signals from direct interference by pump light. We establish a three-phase evolutionary model for hybrid spin ensemble dynamics, yielding a complete analytical solution, and analyze the responses to various spin perturbations. Additionally, we achieve an averaged 38.5 %\%% suppression of the polarization noise and identify the key factors that limit sensitivity improvements. The dynamically polarized comagnetometer exhibits effective suppression of technical noise and holds the potential to overcome quantum noise limit, while offering promising applications in exploring new physics and precise magnetic field measurements.
Abstract Ultra-sensitive comagnetometers, which are designed to detect nuclear- and electron-spin-dependent interaction, have important applications ranging from basic research to inertial navigation systems (INSs). Unfortunately, electric heating, which is typically used in comagnetometers, introduces noise and instability because of the unavoidable generation of a modulated magnetic field. In this study, we investigate and introduce a K-Rb-21Ne comagnetometer that uses laser heating for the first time, when operated in the spin exchange relaxation free regime. The performance of the comagnetometer, which is equipped with both laser heating and electric heating, is investigated, and the two heating modes are compared. The temperature characteristics of the comagnetometer are studied theoretically and experimentally. By optimizing the operating temperature and power density of the pump-light, an equivalent rotation sensitivity of 2.5 × 10 − 7 rad−1 s−1 Hz 1 / 2 @1 Hz is achieved in laser heating mode. The improvement of laser-heating technology could prove essential to reduce electron relaxation and increase the low-frequency sensitivity of comagnetometers. Our results indicate that laser heating can make comagnetometers more suitable for applications in basic research (fifth forces, dark matter, etc), INSs, and other accurate measurements of electronic and nuclear precession.