Several modern precision measurements require a low-noise magnetic shield composed of a MnZn ferrite shield and a multilayer µ-metal shield. However, the residual magnetic field and gradient reduce the performance of the low-noise magnetic shield. An appropriate demagnetization operation is crucial for obtaining a lower residual magnetic field and gradient. This study proposes an improved demagnetization scheme in which the toroidal coil and the solenoidal coil are employed simultaneously, while the ferrite and µ-metal shield layers are wound separately. This allows for a residual field below 0.6 nT and a gradient lower than 0.5 nT cm⁻¹ to be obtained along all three axes within ±20 mm at the center, which is significantly lower than the results published in previous studies. The low-noise magnetic shield used in this study composed of a MnZn ferrite shield with an inner diameter of 112 mm, an outer diameter of 140 mm, and a height of 225 mm, and a five-layer µ-metal shield. This study considerably improves the performance of the low-noise magnetic shields. The proposed scheme can increase the sensitivity of the spin-exchange-relaxation-free atomic magnetometer by approximately 1 fT Hz^-1/2. This study can help apply the low-noise magnetic shield in various fields more conveniently, such as low-field nuclear magnetic resonance detection, atomic gyroscope, and in cutting-edge physics research.

Magnetic field gradients affect numerous modern sensitive measurements and physics studies using atomic ensemble, resulting in the loss of coherence. In some cases, the presence of small gradients can reduce the performance significantly. In this study, we propose an effective in situ method to compensate the triaxial magnetic field gradient for atomic magnetometers, based on multichannel atomic signals in one vapor cell. We design two novel gradient coils by solving closed-form equations to improve the accuracy and efficiency of compensation. We demonstrate the performance of the compensation method in a spin-exchange relaxation-free atomic magnetometer, which reduces the magnetic linewidth by 4.2%–7.6% under the same conditions at a compensation resolution of 50 pT/cm. The proposed coils generate gradients only along two axes and achieve triaxial decoupling, which compensates for the gradient completely without iteration. Our results may aid in suppressing atomic spin relaxations due to magnetic field gradients in several modern measurements and improve their performance, such as the detection of electric dipole moments, ultralow-field nuclear magnetic resonance, and biomagnetism.

This article presents a method for measuring the spin polarization of spin-exchange relaxation-free (SERF) atomic magnetometers at extremely large optical depths. Due to the slowing-down effect, spin polarization can be extracted by measuring the slowing-down factor extracted from the precession frequency. However, this technique is limited by a significant error in the regime of extremely large optical depths, where the pump beam intensity for achieving the optimal spin polarization of alkali atoms is significantly increased. We observed that the instantaneous precession frequency measured in the regime where the spin-exchange rate is not much larger than the Larmor frequency was no longer a constant but varied with the pump beam intensity. Thus, a method for measuring spin polarization based on the ratio of the precession frequency to the measured instantaneous precession frequency is proposed. Based on the proposed method, the spin polarization at a temperature of 473 K and an optical depth of 64 is measured. The measurement results were in accordance with theoretical analysis. The expanded uncertainties of the experimental results varied between 1.8% and 9.6%. The proposed method is also applicable to other atomic devices operated in the SERF regime with extremely large optical depths, such as co-magnetometers and atomic spin gyroscopes.

Ferrite materials are used as magnetic shielding to reduce ultralow magnetic field noise and interference in ultrahigh precision magnetic measurement instruments, including atomic magnetometers. However, there was a shielding coupling between the inner and outer layers of magnetic shields, which affected the shielding effect of the magnetic shields. This study analyzed the magnetic field noise coupling between magnetic shields and measured the residual magnetic field. Then, after demagnetizing and compensating the coil to remove the residual magnetic field, a spin-exchange relaxation-free (SERF) magnetometer was used to study the coupling magnetic field noise on ferrite. A thermal magnetic noise of $210\,\,f^{-1/2}\,\,\cdot $ fT had a significant impact on the magnetic field noise of the Mn–Zn ferrite shield. The sensitivity decreased from 0.737 to 9.223 fT/Hz $^{1/2}$ at 30 Hz, and the magnetic field noise raised to $70.05\,\,f^{-1/2}\,\,\cdot $ fT. The study indicated that the secondary outer layer has a significant impact on the coupling magnetic field noise and magnetic shielding performance of ferrite, while the impact of thermal magnetic noise on the magnetic field noise of ferrite is related to frequency and bandwidth. The research provides a reference for the application of ferrite magnetic shields in atomic magnetometers and the development of shielding devices with wide-frequency electromagnetic shields.

Intrahepatic cholangiocarcinoma (ICC) is a highly aggressive liver cancer characterized by insidious onset, a complex microenvironment, and limited therapeutic options. We present an optical biosensor that applies quantum weak measurement (QWM) to achieve real-time, ultra-sensitive monitoring of Icaritin (ICT) binding to ICC organoids. This innovative platform overcomes the critical limitations of conventional techniques in probing low-concentration and dynamic drug-tumor interactions. By integrating a Mach-Zehnder interferometer with weak value amplification (WVA), the system detects refractive index changes induced by molecular binding with a sensitivity of 2.81×10⁸ nm/M, enabling picomolar-level quantification of ICT kinetics. Using ICC organoids derived from RBE cells as a human ICC model, we demonstrate label-free, real-time binding analysis. This biosensor provides a promising platform for dynamic drug screening and personalized therapy development for ICC.