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 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.
change interaction. In a K-Rb- 21 Ne co-magnetometer which was used for rotation sensing, Rb atomic spins and the 21 Ne nuclear spins couple together by spin exchange. Due to the large Rb density and the Fermi contact constant of Rb- 21 Ne pair, the magnetization field of Rb atomic spins is much larger than that of the K in a K- 3 He co-magnetometer. At the co-magnetometer working point, the precession frequency of Rb atomic spins are much larger than that of the 21 Ne spins. The decay rate and precession frequency of 21 Ne atoms is much smaller than that of the point when the precession frequencies of the Rb and 21 Ne atoms are the same. In this experiment, the dynamics of the Rb- 21 Ne pair at different holding magnetic field point were studied. The frequency response of the co-magnetometer to oscillating magnetic field at different holding magnetic field point was also studied.
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.
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 Stochastic magnetic field noise has a non‐negligible negative impact on the performance of quantum precision measurement instruments such as spin‐exchange relaxation‐free (SERF) co‐magnetometer in terms of sensitivity and stability. Conventional magnetic field error analysis and suppression methods are not applicable to stochastic magnetic field noise. In this paper, a stochastic model of the SERF co‐magnetometer is proposed to analyze the mechanism of stochastic magnetic field noise. The mean and covariance propagation model of the SERF co‐magnetometer is given based on the stochasticity model and statistical principles. The analysis of simulation experiments reveals that reducing the longitudinal electron spin polarization can somewhat reduce the standard deviation of the system output caused by stochastic magnetic field noise. And the atomic ensembles are most resistant to stochastic magnetic field noise when the electron spin polarization strongly couples with the nuclear spin polarization. Finally, the experiments verified the above conclusions. In conclusion, this paper provides theoretical and experimental support for analyzing and suppressing the effect of stochastic magnetic field noise on the SERF co‐magnetometer, which is of great significance for improving the sensitivity and stability of the measurement.
We have studied the polarization of the 85Rb and the fundamental sensitivity of two types of hybrid optical pumping spin exchange relaxation free (SERF) co-magnetometers based on 39K-85Rb-21Ne and 133Cs-85Rb-21Ne with taking the wall relaxation rate into account,which has a big effect on the polarization and fundamental sensitivity,but it is often neglected in the experiments,respectively.The polarization of the 85Rb varies with the thirteen systemic parameters: the number density of buffer gas 21Ne and quench gas N2,frequency rate of pump beam,cell temperature,the photon number flux,mole fraction of 85Rb,cell effective radius,pump beam spot radius,power density of pump beam,input rotation velocity in the x and y direction,external magnetic field in the y and z direction,respectively.The number density of the 21Ne,photon number flux,pump beam spot radius and frequency rate will affect the polarization of the 85Rb greatly by affecting the the pumping rate of pump beam,a magnetic field produced by 85Rb atom spins and experienced by the 21Ne spins.We obtain a general formula on the fundamental sensitivity of the hybrid optical pumping SERF co-magnetometers due to shot-noise,where the fundamental sensitivity varies with the twelve systemic parameters: the number density of buffer gas and quench gas,frequency rate of pump beam,photon number flux,mole fraction of 85Rb,cell effective radius,pump beam spot radius,power density of pump beam,external magnetic field,measurement volume,cell temperature and measurement time.The highest fundamental sensitivity
7.5878×10−11 rad/s/Hz1/2 of 133Cs-85Rb-21Ne co-magnetometer is higher than the ultimate theoretical sensitivity
2×10−10 rad/s/Hz1/2 of K-21Ne co-magnetometer.The fundamental sensitivity limit of the hybrid optical pumping SERF co-magnetometers is superior to
3.7334×10−12 rad/s/Hz1/2.