The long-term bias stability of spin-exchange relaxation-free atomic co-magnetometers is significantly constrained by coupled opto-thermal fluctuations. Traditionally, random systemic offsets at the magnetic compensation point lead to inconsistent opto-thermal coupling, compromising the reproducibility of sensor performance. In this work, we propose a method to simultaneously decouple and suppress these primary drifts by precisely characterizing the physical null-point of the atomic ensemble. A combined compensation scheme, joining residual rotation angle alignment and transverse magnetic field adjustment, is implemented to isolate the sensor output from fluctuations in probe laser intensity and vapor cell temperature. Experimental results demonstrate that the sensitivities to temperature drifts and probe power fluctuations are suppressed simultaneously at the identified null-point by factors of 72 and 880, respectively. This approach establishes a stable zero point, which is expected to significantly enhance sensor reproducibility and stability without sacrificing fundamental sensing performance.
The long-term bias stability of spin-exchange relaxation-free atomic co-magnetometers is significantly constrained by coupled opto-thermal fluctuations. Traditionally, random systemic offsets at the magnetic compensation point lead to inconsistent opto-thermal coupling, compromising the reproducibility of sensor performance. In this work, we propose a method to simultaneously decouple and suppress these primary drifts by precisely characterizing the physical null-point of the atomic ensemble. A combined compensation scheme, joining residual rotation angle alignment and transverse magnetic field adjustment, is implemented to isolate the sensor output from fluctuations in probe laser intensity and vapor cell temperature. Experimental results demonstrate that the sensitivities to temperature drifts and probe power fluctuations are suppressed simultaneously at the identified null-point by factors of 72 and 880, respectively. This approach establishes a stable zero point, which is expected to significantly enhance sensor reproducibility and stability without sacrificing fundamental sensing performance.
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.
Quantum manipulation technology and photoelectric detection technology have jointly facilitated the rapid development of ultra-sensitive atomic spin magnetometers. To improve the output signal and sensitivity of the spin-exchange-relaxation-free (SERF) atomic spin magnetometer, the noises influencing on the output signal and the sensitivity were analyzed, and the corresponding noise suppression methods were presented. The magnetic field noises, including the residual magnetic field noise and the light shift noise, were reduced to approximately zero by employing the magnetic field compensation method and by adjusting the frequency of the pump beam, respectively. With respect to the operation temperature, the simulation results showed that the temperature of the potassium atomic spin magnetometer realizing the spin-exchange relaxation-free regime was 180 °C. Moreover, the fluctuation noises of the frequency and the power were suppressed by using the frequency and the power stable systems. The experimental power stability results showed that the light intensity stability was enhanced 10%. Contrast experiments on the sensitivity were carried out to demonstrate the validity of the suppression methods. Finally, a sensitivity of 13 fT/Hz(1/2) was successfully achieved by suppressing noises and optimizing parameters.
The transverse light-shift can induce non-negligible polarization error in the output signal of spin-exchange relaxation-free (SERF) co-magnetometer. In this paper, a novel method for rapid measurement of transverse light-shift based on the error of steady-state response of co-magnetometer is proposed firstly, then the sources of transverse light-shift in a compact SERF co-magnetometer is modeled and analyzed from three aspects: the non-ideal linear polarization of probe laser, the circular dichroism of the atomic spin ensembles, and the stress-induced birefringence effect of the cell wall. Furthermore, the decoupling and suppression methods of transverse light-shift based on a degree of circular polarization (DOCP) regulation scheme is presented, to realize the decoupling measurement of the transverse light-shift introduced by the whole co-magnetometer cell, and cancel it out with the non-ideal linear polarization of the probe laser. Eventually, the DOCP regulation scheme suggested in this paper achieves more than a 67% suppression ratio in transverse light-shift, and the short- and long-term performance of SERF co-magnetometer are improved due to the reduction of the coupling effect between the probe laser power and transverse field. Moreover, the measurement, decoupling and suppression methods provided in this paper also have the potential to be applied to other atomic sensors, such as the SERF magnetometers and nuclear spin co-magnetometers.
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.
This paper presents a method to reduce the vapor cell temperature error of the spin-exchange-relaxation-free (SERF) magnetometer. The fluctuation of cell temperature can induce variations of the optical rotation angle, resulting in a scale factor error of the SERF magnetometer. In order to suppress this error, we employ the variation of the probe beam absorption to offset the variation of the optical rotation angle. The theoretical discussion of our method indicates that the scale factor error introduced by the fluctuation of the cell temperature could be suppressed by setting the optical depth close to one. In our experiment, we adjust the probe frequency to obtain various optical depths and then measure the variation of scale factor with respect to the corresponding cell temperature changes. Our experimental results show a good agreement with our theoretical analysis. Under our experimental condition, the error has been reduced significantly compared with those when the probe wavelength is adjusted to maximize the probe signal. The cost of this method is the reduction of the scale factor of the magnetometer. However, according to our analysis, it only has minor effect on the sensitivity under proper operating parameters.
Spin-exchange relaxation-free (SERF) co-magnetometers, characterized by high sensitivity, compactness, and low drift, show great potential in quantum precision measurements based on atomic ensembles. However, periodic fluctuation noise—originating from laser intensity instability, heating signal crosstalk, and electronic interference—induces oscillatory artifacts in Allan variance analysis, degrading measurement accuracy and long-term stability. This study presents a periodic noise suppression scheme based on jointly optimized finite impulse response (FIR) notch filters, implemented for the first time in a SERF co-magnetometer. By precisely shaping the amplitude response through least-squares optimization, the scheme achieves targeted attenuation of interference frequencies. Experimental results confirm that the proposed method effectively suppresses periodic noise, yielding smoother Allan variance curves and significantly enhancing measurement stability. The proposed approach offers a practical and generalizable solution for improving the precision of atomic sensors and provides technical guidance for noise mitigation in broader precision measurement applications.