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Measurement Science and Technology

Study of magnetic field error suppression methods based on atomic parameters of cell in atomic co-magnetometer rotation measurement

Ye Liu, Wenfeng Fan, Yao Liu, Longyan Ma, Jiale Quan, Shouzeng Zhou, Haoying Pang, Wei Quan

Published Nov 11, 2024• 11 citations
Publisher

Abstract

Abstract We propose a new model for magnetic field errors based on the rotation measurement of the K-Rb- 21 Ne co-magnetometer, considering the density ratio and spin collisions. The spin polarization characteristics of different alkali metal density ratios were analyzed by creating five cells with different density ratios, and the correctness of the magnetic field error model was verified experimentally. Moreover, the effects of five different alkali metal density ratios of cells on the sensitivity, long-term stability and magnetic field error suppression of the K-Rb- 21 Ne co-magnetometer were investigated experimentally. When the density ratio is 1:107, there can be the optimal magnetic field error suppression effect, sensitivity and long-term stability. According to the derived magnetic field error equation, the magnetic noise error of the K-Rb- 21 Ne co-magnetometer with an optimized density ratio is reduced by nearly 5 times from 260°/h/nT to 56.5°/h/nT, the sensitivity is improved from 2.9×10 −5 °/s/Hz 1 / 2 to 7.0×10 −6 °/s/Hz 1 / 2 at 1 Hz, and the long-term stability Allan variance over two hours is improved from 1.9×10 −2 °/h to 8.9×10 −3 °/h. This result provides a theoretical basis for designing the parameters of the K-Rb- 21 Ne co-magnetometer cell.

DOI
10.1088/1361-6501/ad90fd

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IEEE Transactions on Instrumentation and Measurement•Jan 1, 2022•19 citations
Abstract We propose a new model for magnetic field errors based on the rotation measurement of the K-Rb- 21 Ne co-magnetometer, considering the density ratio and spin collisions. The spin polarization characteristics of different alkali metal density ratios were analyzed by creating five cells with different density ratios, and the correctness of the magnetic field error model was verified experimentally. Moreover, the effects of five different alkali metal density ratios of cells on the sensitivity, long-term stability and magnetic field error suppression of the K-Rb- 21 Ne co-magnetometer were investigated experimentally. When the density ratio is 1:107, there can be the optimal magnetic field error suppression effect, sensitivity and long-term stability. According to the derived magnetic field error equation, the magnetic noise error of the K-Rb- 21 Ne co-magnetometer with an optimized density ratio is reduced by nearly 5 times from 260°/h/nT to 56.5°/h/nT, the sensitivity is improved from 2.9×10 −5 °/s/Hz 1 / 2 to 7.0×10 −6 °/s/Hz 1 / 2 at 1 Hz, and the long-term stability Allan variance over two hours is improved from 1.9×10 −2 °/h to 8.9×10 −3 °/h. This result provides a theoretical basis for designing the parameters of the K-Rb- 21 Ne co-magnetometer cell.
The K-Rb-21Ne co-magnetometer exhibits poorer dynamic performance due to the larger equivalent magnetic field generated by alkali metal atoms. In this study, the impact of the atomic number density of alkali metal atoms and noble gas atoms in the cell on the dynamic performance of the atomic ensemble is investigated quantitatively. Relationships between the slow-decay term in the transient response attenuation of the Spin-Exchange Relaxation-Free (SERF) co-magnetometer to interference magnetic fields and the number densities of noble gas atoms as well as alkali metal atoms are established. Based on the established model, the relationship between the number density of 21Ne atoms and dynamic performance is investigated using cells with five different noble gas pressures. Then, we investigate the impact of the number density of alkali metal atoms using a cell with a pressure of 2.1 atm at different temperatures. The results indicate that, as the number density of alkali metal atoms or noble gas atoms in the cell increases, the dynamic performance of the system improves, which provides a theoretical basis for the design of cell parameters for SERF co-magnetometers.
Abstract In a K-Rb- 21 Ne co-magnetometer, the Rb electron magnetic field which is experienced by the nuclear spin is about 100 times larger than that of the K in a K- 3 He co-magnetometer. The large electron magnetic field which is neglected in the K- 3 He co-magnetometer coupled Bloch equations model is considered here in the K-Rb- 21 Ne co-magnetometer to study the low frequency magnetic field suppression effect. Theoretical analysis and experimental results shows that in the K-Rb- 21 Ne spin co-magnetometer, not only the nuclear spin but also the large electron spin magnetic field compensate the external magnetic field noise. By comparison, only the 3 He nuclear spins mainly compensate the external magnetic field noise in a K- 3 He co-magnetometer. With this study, in addition to just increasing the magnetic field of the nuclear spins, we can suppress the magnetic field noise by increasing the density of the electron spin. We also studied how the magnetic field suppression effect relates to the scale factor of the K-Rb- 21 Ne co-magnetometer and we compared the scale factor with that of the K- 3 He co-magnetometer. Lastly, we show the sensitivity of our co-magnetometer. The magnetic field noise, the air density fluctuation noise and pumping power optimization are studied to improve the sensitivity of the co-magnetometer.
Abstract Atomic co-magnetometers can be utilized for high-precision angular velocity sensing or fundamental physics tests. The sensitivity of a co-magnetometer determines the angle random walk of an angular velocity sensor and the detection limit for a fundamental physics test. A high-sensitivity K-Rb-21Ne co-magnetometer, which is utilized for angular velocity sensing, is presented in this paper. A new type of spin relaxation of Rb atom spins, which can broaden the zero-field magnetic resonance lines of the co-magnetometer, is discovered. Further studies show that the spin relaxation of Rb atoms is caused by a high Rb electron magnetization field. With this discovery, the total relaxation rate of Rb atoms is optimized to improve the sensitivity of the co-magnetometer. Moreover, its sensitivity is optimized by suppressing various noises. Especially, to suppress laser-related noises, the co-magnetometer is designed such that the sensitive axis of the co-magnetometer can be fixed to the direction in which the projection input of the earth’s rotation is 0. This is called a rotating co-magnetometer. A magnetic field sensitivity of 1.0 fT/Hz−1/2@5 Hz, which is equal to an angular velocity sensitivity of 2.1 × 10−8 rad s−1 Hz−1/2@5 Hz, is demonstrated using a spherical vapour cell with a diameter of 14 mm.
Abstract The alkali-metal density ratio is one of the primary design parameters in hybrid optical pumping magnetometers. Here, experiments were conducted with a hybrid optically-pumped atomic magnetometer using a cell containing potassium and rubidium. Potassium atoms are pumped by a laser and become polarized. Rubidium atoms are polarized via collisions with potassium atoms and can be probed. The light shift was eliminated by adjusting the density ratio of potassium to rubidium atoms and by optimizing the pump laser parameters. The effect of fluctuations in the laser power and frequency were minimized as a result. The optimal density ratio and magnetic field sensitivity were 1:277 and 0.68 fT Hz −1/2 , respectively.
An all-optical atomic spin magnetometer using a hybrid cell of K and Rb atoms is demonstrated in this paper. Via deriving and solving the Bloch equations, we established the models for the polarization rate of Rb and the magnetometer’s output signal, respectively. In order to achieve the maximum sensitivity, we carried out research on the influence of the pump power on the polarization rate and magnetometer’s output signal. The magnetometer’s sensitivity was found to be proportional to the polarization rate of Rb, which was confined by the pump power. In a certain context, theoretical predictions indicated that the larger the pump power was, the higher magnetometer’s sensitivity that could be realized. However, the theoretical estimate deviated from the experimental results. An analysis of the errors between the actual value and the theoretical value showed that the different molar ratio between the two species of alkali-metal atoms was the primary reason causing the deviation. By comparing the experimental measurement result with simulation result, we found the difference in the molar ratio to be approximate 4 times. After various parameters had been optimized, a sensitivity of 18 fT/Hz 1/2 was achieved by analyzing the signal-to-noise ratio.
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.