The ultra-sensitive atomic co-magnetometer based on the spin-exchange relaxation-free (SERF) regime is a valuable tool for inertial measurements and fundamental physics research. However, the optical magnetic misalignment effect is a significant source of error in SERF co-magnetometers, limiting their magnetic field suppression ability and long-term stability. This paper establishes a response model of angular velocity and magnetic field for the SERF co-magnetometer. The impact of optical magnetic misalignment on the scale factor, magnetic field amplitude-frequency response, and angular velocity errors caused by magnetic noise is systematically investigated. The results indicate that the scale factor and magnetic field suppression ability decrease as the optical magnetic misalignment angle increases, while the angular velocity errors caused by magnetic noise increase as the misalignment angle increases. Finally, experimental results demonstrate that the optical-magnetic misalignment effect significantly compromises the long-term stability of SERF co-magnetometers, underscoring its substantial influence on the overall performance. This work contributes to understanding the mechanism of optical magnetic misalignment effects on the SERF co-magnetometer and enhances its performance.
The ultra-sensitive atomic co-magnetometer based on the spin-exchange relaxation-free (SERF) regime is a valuable tool for inertial measurements and fundamental physics research. However, the optical magnetic misalignment effect is a significant source of error in SERF co-magnetometers, limiting their magnetic field suppression ability and long-term stability. This paper establishes a response model of angular velocity and magnetic field for the SERF co-magnetometer. The impact of optical magnetic misalignment on the scale factor, magnetic field amplitude-frequency response, and angular velocity errors caused by magnetic noise is systematically investigated. The results indicate that the scale factor and magnetic field suppression ability decrease as the optical magnetic misalignment angle increases, while the angular velocity errors caused by magnetic noise increase as the misalignment angle increases. Finally, experimental results demonstrate that the optical-magnetic misalignment effect significantly compromises the long-term stability of SERF co-magnetometers, underscoring its substantial influence on the overall performance. This work contributes to understanding the mechanism of optical magnetic misalignment effects on the SERF co-magnetometer and enhances its performance.
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.
The atomic comagnetometers (ACMs) based on the spin-exchange relaxation-free (SERF) regime exhibit extremely high sensitivity in angular velocity measurements, positioning them as leading candidates for next-generation precision inertial sensing. However, magnetic noise remains a significant factor that contributes significantly to long-term bias drift. Here, a comprehensive model in full-frequency band of the angular velocity measurement error induced by magnetic noise in ACMs is established. Based on the proposed model, what we believe to be a new method is proposed to reduce magnetic noise error by suppressing the magnetic field response in the mid-frequency range. After optimizing the temperature of the vapor cell to minimize the magnetic field response in the mid-frequency range, the angular velocity measurement error caused by magnetic noise was reduced by 20.4%, and the bias drift was improved by 34.8%. The theories and methods proposed in this study innovatively highlight the critical role of mid-frequency magnetic field responses in suppressing magnetic noise errors, and provide important guidance for improving bias drift in SERF ACMs.
Ultrasensitive atomic comagnetometers (ACMs) are invaluable tools for both inertial measurement and fundamental physics research. However, the misalignment between the pump light and the main magnetic field affects the polarization characteristics of nuclear spins of the noble gas atoms, making it a significant source of noise. In this article, an atomic magnetometer response model with the optical-magnetic misalignment error is established, and the mechanism of the influence of optical-magnetic misalignment on nuclear spin polarization is analyzed. An in situ evaluation method and a suppression method of optical-magnetic misalignment error are proposed, and their effectiveness is verified through experiments with varying pump light incidence directions. The experimental results indicate that after optical-magnetic alignment using the proposed method, the spin polarization of the coupled atomic ensemble is enhanced by 20.7%, and the longitudinal relaxation rate of the nuclear spin is reduced by 6.9%. Additionally, the amplitude-frequency response (AFR) of the x-axis magnetic field is reduced by 33.2% at 1 Hz and by 53.1% at frequencies below 0.002 Hz. This indicates an improvement in the transverse magnetic field error suppression capability of the ACMs.
Magnetic field gradients interfere with the coherence of the atomic ensemble and degrade the performance of the spin-exchange relaxation-free (SERF) atomic magnetometer. In this paper, the influence of magnetic field gradients is incorporated into the response model of single-beam atomic magnetometer, and the theoretical models of transverse relaxation rate, spin polarization and scale factor are established. Based on this model,we find that magnetic field gradients in different directions can cause varying degrees of degradation in the performance parameters of the magnetometer. The magnetic linewidths under different light power and magnetic field gradients are measured using the designed dedicated magnetic field gradients coils, and the spin polarization and magnetic field gradients relaxation rate are obtained through fitting. An unevenness and deviation of the curve are also observed in the experiments, indicating the presence of the magnetic field gradient of approximately 2 nT/cm in the magnetic shields. Furthermore, in a magnetic field gradient environment of 20 nT/cm, the mean of the long-term sensitivity decreased by 3.5 times and the standard deviation increased by 11 times. It shows that the magnetic field gradients will not only affect the signal-to-noise ratio, but also make the magnetometer more vulnerable to external interference when working. The sensitivity and stability of magnetometer will be greatly reduced. The research in this article provides a theoretical and experimental basis for eliminating the influence of magnetic field gradients and improving the accuracy of magnetic field measurements.
Optical rotation detection systems are widely used in various kinds of atomic sensors, such as atomic magnetometers, co-magnetometers, and nuclear magnetic resonance (NMR) gyroscopes; and appear in many applications such as fundamental physics, biomagnetism, magnetism test, etc. The study analyses the frequency responses to three-axis dynamic magnetic fields in optical rotation detection systems (ORDS) of Spin-Exchange Relaxation-Free (SERF) magnetometers. Because of the imperfections of the optical elements, the probe light is actually elliptically polarised in ORDS, which can polarise the atom ensemble and cause the responses to the three-axis magnetic field. Theoretically it analyse the frequency responses to the sinusoidal magnetic field, and prove that the responses are closely associated with the DC magnetic field. The values of the DC magnetic fields are calculated with special frequency points, called ‘break points’, in the transverse responses. The relationships between the DC magnetic field and the sensitivities of ORDS, and effectively suppress the magnetic noise responses with the residual magnetic field compensation. The paper demonstrated the influence of elliptically polarised light on the sensitivity of ORDS in SERF magnetometers. The elliptically polarised probe light polarises the alkali atom ensemble, which leads to the responses of the magnetic noise in the shield. Finally, the sensitivity of ORDS is improved by approximately two times at 10-20 Hz. This method is beneficial for improving probe sensitivity in SERF magnetometers, co-magnetometers, and NMR gyroscopes.
Heating the alkali metal vapor cell to obtain high atomic density is a prerequisite for realizing the high-precision measurement for spin-exchange relaxation-free (SERF) co-magnetometer. However, the thermo-magnetic and thermo-optical coupling noise caused by the temperature diffusion from the alkali vapor cell is one of the main factors restricting the co-magnetometer performance at present. Here the influence of heating on the SERF co-magnetometer was comprehensively studied, and the thermal error model of the system was established. A novel heat insulation structure for the co-magnetometer was designed, and the effectiveness was verified through monitoring of characteristic temperature points. Compared to the conventional oven support, the average maximum temperature difference within 12 h of the optical path and magnetic shielding systems (OPMSS) decreased by 52%, the bias instability of the co-magnetometer decreased by 24%, and the noise of the co-magnetometer at 1 Hz decreased by 33%. The experimental results demonstrate that this method reduces the temperature fluctuation of the OPMSS, effectively suppresses the thermal coupling noise, and thus improves the performance of the SERF co-magnetometer. Moreover, this method is also applicable to other quantum sensors based on alkali metal vapor cell.