The deterioration of spin coherence has been a significant challenge in the field of quantum magnetic measurements based on optically pumped atomic magnetometers (OPAMs). However, measurement and evaluation methods for specific relaxation components of OPAMs under working conditions remain lacking, which impedes further improvement in OPAM performance. To address this, we propose a methodology for quantifying the relaxation components of an OPAM under realistic operating conditions. Using this method, we confirm the existence of an anomalous relaxation mechanism induced by radio-frequency (RF) magnetic fields and develop an empirical expression to describe its behavior. The results experimentally demonstrate that, in addition to the well-known spin-exchange relaxation, the dominant contributions to spin relaxation arise from optical pumping and RF magnetic fields. This work paves the way for sensitivity enhancement in quantum magnetometry and refines the theoretical understanding of relaxation mechanisms in OPAMs.
The deterioration of spin coherence has been a significant challenge in the field of quantum magnetic measurements based on optically pumped atomic magnetometers (OPAMs). However, measurement and evaluation methods for specific relaxation components of OPAMs under working conditions remain lacking, which impedes further improvement in OPAM performance. To address this, we propose a methodology for quantifying the relaxation components of an OPAM under realistic operating conditions. Using this method, we confirm the existence of an anomalous relaxation mechanism induced by radio-frequency (RF) magnetic fields and develop an empirical expression to describe its behavior. The results experimentally demonstrate that, in addition to the well-known spin-exchange relaxation, the dominant contributions to spin relaxation arise from optical pumping and RF magnetic fields. This work paves the way for sensitivity enhancement in quantum magnetometry and refines the theoretical understanding of relaxation mechanisms in OPAMs.
The light shift represents a major source of measurement error and system noise in optically pumped atomic magnetometers (OPAMs). Tuning the laser frequency to a specific value is a common and effective approach to suppressing light shift in many optical-pumping systems. However, when this method is applied to OPAMs, a significant issue arises: at the zero-light-shift frequency, the magnetometer’s sensitivity decreases markedly. Consequently, it is not possible to optimize simultaneously both the measurement accuracy affected by the light shift and the overall sensitivity of the magnetometer. To address this contradiction, the underlying mechanism was analyzed using the theory of light absorption and the principles governing light–atom interactions, leading to the proposal of a dual-frequency optical-pumping scheme. Experimental results demonstrate that this approach can suppress the light shift by more than 95% while maintaining the optimal sensitivity of the OPAM. The proposed dual-frequency scheme can also be extended to other circularly polarized optical-pumping systems, thereby facilitating both the enhancement of OPAM performance and its practical deployment in real-world applications.
The magnetic field gradient within optical pumping magnetometers (OPMs) suppresses sensitivity improvement. We investigated the effects of the magnetic field gradient along the x-, y-, and z-axes on the limiting factors of magnetometers under extremely low magnetic field conditions. We modified the magnetic field gradient relaxation model such that it can be applied to atoms in the spin exchange relaxation free (SERF) regime. The gradient relaxation time and spin polarizations, combined with fast spin-exchange interaction, were determined simultaneously using the oscillating cosine magnetic field excitation and amplitude spectrum analysis method. During the experiments, we eliminated the errors caused by the temperature and pumping power, and considered different isotope spin exchange collisions in naturally abundant Rb during the data analysis to improve the fitting accuracy. The experimental results agreed well with those of theoretical calculations and confirmed the accuracy of the improved model. The contribution of the transverse magnetic field gradient to the relaxation of the magnetic field gradient cannot be ignored in the case of small static magnetic fields. Our study provides a theoretical and experimental basis for eliminating magnetic gradient relaxation in atomic sensors in the SERF region.
Traditional practice of suppressing low-frequency noise in atomic magnetometers is mainly through the application of magnetic field modulation, while magnetic fields of this kind introduce extra transverse relaxation, which results in a decrease of sensitivity. In this study, a novel method of measuring relaxation rate induced by spin-destruction, wall collisions and modulation magnetic fields is proposed. The optical pumping model is studied both in optical-thin and optical-thick vapor cell through the analysis of total relaxation, thus the optical pumping rate can be separated from total relaxation by analyzing the optical depth. Furthermore, based on the analysis of optical pumping rate and relaxation rate, the polarization of the electron ensemble was evaluated. A compact magnetometer with single-beam configuration is developed for the proof of concept, and the experimental results show good agreements with theoretical calculation. Our method provides a simple and feasible approach to in-situ measurement of transverse relaxation rate and optical pumping rate with physical structure of the device untouched, which is especially advantageous for designing and optimizing compact atomic magnetometers.
Phase error is one of the primary factors leading to deviations between the readings of alkali-metal optically pumped atomic magnetometers (OPAMs) operating in closed-loop mode and the true magnetic field values. Because the phase error varies significantly with both the magnitude of the measured magnetic field and the orientation of the probe relative to the field direction, it imposes a major limitation on the use of OPAMs in real geomagnetic environments. To address this issue, a rapid suppression method for phase error in closed-loop OPAM operation is proposed. Specifically, the azimuth, pitch, and rotation angles are employed to quantitatively characterize the spatial orientation of the measured magnetic field with respect to the probe, and the phase error is measured and calibrated under closed-loop conditions. Experimental results indicate that the phase error mainly arises from changes in the rotation angle and the magnitude of the magnetic field, and is essentially insensitive to variations in azimuth and pitch angles. Based on this calibration, the effectiveness of the proposed suppression method was verified. When the instantaneous fluctuation of the phase error is less than π /6, the method can suppress the phase error to within π /180 within one second, with negligible impact on the OPAM’s dynamic performance. This work provides a dynamic phase error suppression approach for OPAMs, refines the theoretical understanding of OPAM phase errors, and lays a solid foundation for their design and application in geomagnetic environments.
The light shift is a significant error source of optically pumped atomic magnetometers (OPAMs), requiring accurate calculation or measurement to assess its impact on the accuracy of OPAMs. In this paper, a light shift theoretical model considering the gradient of the pump light is established, providing a detailed description of the light shift distribution within the cell under the influence of multiple parameters. Additionally, a light shift measurement method through magneto optical angle adjustment (MOAA) is proposed, enabling convenient measurement of the light shift. The correctness of the proposed model and the effectiveness of the MOAA method are validated through experiments. The proposed model and method contribute to improving the accuracy of OPAMs and enhancing their performance in practical applications.
Optically pumped atomic magnetometer (OPAM), as a highly sensitive quantum sensor, is often significantly disturbed by low-frequency random noise, which seriously limits its measurement robustness. Motivated by this problem, we systematically studied the influence of various parameters of the statistical field related to random telegraph noise (RTN) on the dynamics and spectral characteristics of the OPAM, both theoretically and experimentally. The investigation revealed that the OPAM output spectrum shows a phase sensitivity similar to that induced by the squeezed vacuum field to the relative phase ϕ between the statistical field and the coherent driving field, and its physical essence originates from the phase-dependent reservoir formed by the statistical field. Specifically, the system spectrum is periodically modulated to ϕ , showing complementary regulation behavior of spectral peak and linewidth: when ϕ =90 ∘ , the system is almost insensitive to the RTN noise parameters, showing good robustness; however, when ϕ =0 ∘ , the system is highly responsive to the RTN parameters, showing obvious spectral broadening effect. Our results not only provide what we believe to be a new phase control strategy for the optimization of the OPAM under the background of low-frequency noise, but also provide theoretical and experimental path for the development of noise spectrum precision measurement and dynamical decoupling technology based on OPAM.