On the relaxation of the longitudinal magnetization of the X-Y model

Martine Dumont

Zhenglong Lu, Jiali Liu, Xin Zhao +5 more

Abstract The relaxation rate is a fundamental parameter that characterizes the dynamics of atomic ensembles and plays a critical role in the performance of atomic magnetometers. In this study, a transient dynamics model for the NMOR magnetometer is developed based on multipole moment theory, revealing that the decay rate of the transient response to a step magnetic field from zero to certain value is determined by both transverse and longitudinal relaxation rates, whereas that to a step magnetic field from certain value to zero depends solely on the longitudinal relaxation rate. This distinction enables the independent determination of the two relaxation rates. To validate the proposed method, transverse and longitudinal relaxation rates are experimentally measured under various laser powers, which are consistent with the Lorentzian linewidths extracted from magnetic resonance curve fitting. This study provides valuable insights into atomic transient dynamics and contributes to the fast measurement of relaxation rates in NMOR magnetometers.

Marvin D. Girardeau

Shuying Wang, Jixi Lu, Kaixuan Zhang +3 more

Zero-field atomic ensembles enable the development of ultrahigh-sensitivity magnetometry. However, their intrinsic insensitivity to longitudinal magnetic fields along the pumping direction poses a fundamental limitation, restricting precise weak-field quantification and complex system decoupling. Herein, we propose a novel zero-field weak parametric modulation scheme capable of ultrahigh-sensitivity extraction of longitudinal magnetic fields. Transverse modulation is employed to manifest the electron spin polarization projection induced by the longitudinal fields. Based on the perturbation model established, first-order parametric resonance associated with the longitudinal magnetic field yields significant signal enhancement under low-frequency and weak modulation conditions, while simultaneously suppressing spin-exchange relaxation caused by magnetic field modulation. We experimentally achieved a longitudinal measurement sensitivity of 16 fT / Hz 1 / 2 , more than an order of magnitude improved over traditional schemes, with a bandwidth of 70 Hz. Benefiting from low spin relaxation, the noise floor of the transverse magnetic field measurement is preserved at 4 fT / Hz 1 / 2 . The proposed scheme pushes the boundaries of existing weak magnetic field measurement, providing critical capabilities for state-of-the-art precision experiments including new physical quantity detection.

Marvin D. Girardeau

Xiang Zhan, Jiang Qiyuan, Wang Zhiguo +2 more

We proposed a new bias-approach method for measuring longitudinal relaxation time of 129Xe. Compared with the delayed pulse method, the measuring time of the proposed single-scan bias-approach is significantly decreased by more than 20 times, and the differences are 2% and 0.7% of two sample cell A and B respectively. By giving a small static magnetic field in the transverse domain, a π-pulse-induced 87Rb magnetometer signal bias with respect to the longitudinal magnetization of xenon was obtained. We then use a π/2 pulse to find the half-life time of longitudinal relaxation. Since the bias-approach has a low requirement of the systematic robust, it naturally becomes a more efficient method to measure the longitudinal relaxation time with respect to the noble gas in the vapor cell.