Maintenance of self-compensated state in a K-Rb-21Ne atomic comagnetometer via manipulation of time-varying pump light and photoelectric feedback control
We theoretically develop a method for maintaining the self-compensated state of a K-Rb21Ne comagnetometer, which is one of the core problems in optimizing the detection sensitivity of the comagnetometer to fundamental interactions and inertial rotation. The result of Rb21Ne coupling dynamics under transverse cosinusoidal magnetic field modulation can present a dispersive response with respect to the varying 21Ne nuclear magnetic field Bn, in which a monotonic interval can be used to monitor the drift of Bn. Furthermore, the result of Rb spin poparization evolution under the constraint of self-compensated-state maintenance exhibits a large enough time scale relative to Rb spin relaxation that it can be regarded as a quasi-static process, thus the adopted time-varying pump light intensity can be obtained using Rb equilibrium polarization. Accordingly, an implementation scheme is given. This method can not only compensate the drifting �", but also promote the system to return back to the original self-compensated state through manipulation of atomic polarization via time-varying pump light, which is useful in stabilizing the system performance.
We theoretically develop a method for maintaining the self-compensated state of a K-Rb21Ne comagnetometer, which is one of the core problems in optimizing the detection sensitivity of the comagnetometer to fundamental interactions and inertial rotation. The result of Rb21Ne coupling dynamics under transverse cosinusoidal magnetic field modulation can present a dispersive response with respect to the varying 21Ne nuclear magnetic field Bn, in which a monotonic interval can be used to monitor the drift of Bn. Furthermore, the result of Rb spin poparization evolution under the constraint of self-compensated-state maintenance exhibits a large enough time scale relative to Rb spin relaxation that it can be regarded as a quasi-static process, thus the adopted time-varying pump light intensity can be obtained using Rb equilibrium polarization. Accordingly, an implementation scheme is given. This method can not only compensate the drifting �", but also promote the system to return back to the original self-compensated state through manipulation of atomic polarization via time-varying pump light, which is useful in stabilizing the system performance.
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.
Self-compensated comagnetometers, employing overlapping samples of spin-polarized alkali and noble gases (for example K-3He) are promising sensors for exotic beyond-the-standard-model fields and high-precision metrology such as rotation sensing. When the comagnetometer operates in the so-called self-compensated regime, the effective field, originating from contact interactions between the alkali valence electrons and the noble-gas nuclei, is compensated with an applied magnetic field. When the comagnetometer begins operation in a given magnetic field, spin-exchange optical pumping establishes an equilibrium between the alkali electron-spin polarization and the nuclear-spin polarization. Subsequently, when the magnetic field is tuned to the compensation point, the spin polarization is brought out of the equilibrium conditions. This causes a practical issue for long measurement times. We report on a method for closed-loop control of the compensation field. This method allows optimization of the operating parameters, especially magnetic field gradients, in spite of the inherently slow (hours to days) dynamics of the system. With the optimization, higher stable nuclear polarization, longer relaxation times, and stronger electron-nuclear coupling are achieved which is useful for nuclear-spin-based quantum memory, spin amplifiers, and gyroscopes. The optimized sensor demonstrates a sensitivity comparable to the best previous comagnetometer but with four times lower noble-gas density. This paves the way for applications in both fundamental and applied science.
As a novel quantum sensor utilizing atomic spin coupling mechanisms, spin-exchange relaxation-free (SERF) comagnetometers demonstrate promising applications in precision metrology such as magnetic field and rotation sensing. However, the ultra-high precision measurement capability exhibits vulnerability to multiple disturbance factors, with pump light intensity fluctuations emerging as a critical instability source that compromises operational reliability during prolonged measurements. In this paper, a model-driven paradigm for pump light intensity error suppression in SERF comagnetometers is proposed. The nonlinear dynamics are rigorously linearized via Taylor expansion within their valid range to construct a state-space model, ultimately deriving the pump light intensity frequency response model. The proposed methodology undergoes experimental validation on a K-Rb-21Ne comagnetometry platform, confirming the predictive capability for stability degradation mechanisms. Through theoretical analysis and experimental verification, this study reveals that magneto-optical non-orthogonality, which introduces a differential component in the light intensity transfer function, creates an approximate proportional relationship between the output signal and pump light intensity within the operating bandwidth. Light intensity noise is decomposed, and light intensity errors are quantitatively evaluated via the frequency response model. To address this critical issue affecting inertial measurement accuracy, a closed-loop control-based suppression method with optimized feedback gain is proposed. By dynamically adjusting the closed-loop feedback gain through real-time intensity monitoring, the intensity instability associated with optical pumping is suppressed from 0.56% to 0.14%, concomitant with a 2.8-fold improvement in the long-term stability of the SERF comagnetometer.
The elimination of relaxation resulting from spin-exchange (SE) interaction is crucial for ultrasensitive atomic comagnetometers. In this study, we demonstrate the SE relaxation is only partially suppressed and significantly broadens the magnetic linewidth in the K-Rb-21Ne comagnetometer. The SE relaxation arises from the compensation magnetic field when operating in the self-compensation regime. We propose a new method to measure the SE relaxation in the self-compensation regime where the alkali-metal and noble-gas spin ensembles are coupled. In the presence of SE relaxation, we find the optimal alkali-metal polarization for maximizing the sensitivity is shifted from the typical value. Under various conditions, we present a detailed study of the SE relaxation and the scale factor as a function of alkali-metal polarization, which are further verified by the theoretical models. The reduction of SE relaxation and improvement of scale factor by using 87Rb atoms is also studied.
• A dual-spectrum feedback architecture based on conventional closed-loop control is proposed, enabling real-time compensation for spin polarization error (SPE) in the K-Rb-21Ne atomic spin gyroscope, significantly enhancing long-term stability. • An adaptive dynamic control strategy based on a Lyapunov function is introduced to replace PID control, optimizing control parameters and improving system response speed and stability. • Experimental results show that the method improves SPE suppression by 54.4%, 74.5%, and 74.6% for clustering times of 100s, 500s, and 1000s, respectively. • Interference tests demonstrate that the method effectively eliminates steady-state offsets and enhances the system's adaptability to power density and polarization fluctuations, providing a long-term stability solution for optically pumped atomic devices. The long-term stability of atomic spin polarization plays a critical role in ensuring the sustained stability of atomic gyroscope outputs. However, drift in the laser pumping rate introduces the spin polarization error (SPE), necessitating high-precision closed-loop stabilization. Conventional single-beam-splitting closed-loop control methods overlook the time-varying characteristics of beam-splitting elements during prolonged operation, resulting in incomplete suppression of SPE in long-term measurements. To address this limitation, a dynamic light compensation framework is developed for the analysis and suppression of SPE in an atomic spin gyroscope. The proposed structure enables real-time monitoring of parameter variations in the beam-splitting elements and feeds this information back into the control loop to actively compensate for polarization errors induced by optical drift. Furthermore, an adaptive control method based on nonlinear inversion and disturbance observation is introduced, which estimates the internal state and compensates time-varying parameters in real time, thereby replacing conventional PID control and ensuring optimal closed-loop performance. Experimental results from a K-Rb- 21 Ne atomic gyroscope demonstrate real-time suppression of SPE, with improvements of 54.4%, 74.5%, and 74.6% for clustering times of 100, 500, and 1000 seconds, respectively. Interference tests show enhanced response speed and the elimination of steady-state offsets under power density and polarization disturbances. This method offers a novel solution for achieving long-term stability in optically pumped atomic devices, ensuring sustained measurement accuracy.
Zero‐Position Closed‐Loop Control of Nuclear Spin in a K‐Rb‐21Ne21Ne Comagnetometer
Abstract In SERF (spin‐exchange relaxation‐free) comagnetometers, the fluctuation of the atomic ensemble's polarization significantly impacts the long‐term stability of the output signal. A real‐time closed‐loop control method for the nuclear spin polarization is proposed, and the measurement model is established using Kalman state observer. Furthermore, magnetic field control signals are generated using a proportional‐integral‐derivative (PID) strategy, which is then applied to the atomic ensemble to dynamically adjust the nuclear spin polarization. Finally, closed‐loop control of nuclear spin polarization is achieved through continuous feedback and control. Moreover, experiments have demonstrated that implementing a closed‐loop system for nuclear spin zero‐position is conducive to reducing the sensitivity of the output signal to fluctuations in the external environment. The experimental results show that the Allan deviation at 100 s is reduced by , and the sensitivity of inertial rotation measurement is significantly improved, that is, the noise level at 1 Hz is suppressed by approximately .