High-sensitivity total-field atomic magnetometer enables brain-activity measurements in unshielded Earth’s field.

Magnetocardiography (MCG), which uses high-sensitivity magnetometers to record magnetic field signals generated by electrical activity in the heart, is a noninvasive method for evaluating heart diseases such as arrhythmia and ischemia. The MCG measurements usually require the participant keeping still in a magnetically shielded room due to the immovable sensor and noisy external environments. These requirements limit MCG applications, such as exercise MCG tests and long-term MCG observations, which are useful for early detections of heart diseases. Here, we introduce a movable MCG system that can clearly record MCG signals of freely behaving participants in an unshielded environment. On the basis of optically pumped magnetometers with a sensitivity of 140 fT/Hz^1/2, we successfully demonstrated the resting MCG and the exercise MCG tests. Our method is promising to realize a practical movable multichannel unshielded MCG system that nearly sets no limits to participants and brings another kind of insight into the medical diagnosis of heart disease.

Searching for beyond-the-standard-model interactions has been of interest in quantum sensing. Here, we demonstrate a method, both theoretically and experimentally, to search for the spin- and velocity-dependent interaction with an atomic magnetometer at the centimeter scale. By probing the diffused optically polarized atoms, undesirable effects coming along with the optical pumping, such as light shifts and power-broadening effects, are suppressed, which enables a $1.4{\mathrm{fT}}_{\mathrm{rms}}/{\mathrm{Hz}}^{1/2}$ noise floor and the reduced systematic errors of the atomic magnetometer. Our method sets the most stringent laboratory experiment constraints on the coupling strength between electrons and nucleons for the force range $\lambda >0.7\mathrm{mm}$ at $1\sigma$ confidence. The limit is more than 3 orders of magnitude tighter than the previous constraints for the force range between $1\mathrm{mm}\sim 10\mathrm{mm}$, and one order of magnitude tighter for the force range above 10 mm.

Spin-exchange collisions among alkali-metal atoms affect the coherence time and gyromagnetic ratio of atoms by redistributing the ground-state population. We theoretically study the interactions between magnetic fields and atoms in the presence of spin-exchange collisions. Using the modified Bloch equations derived from the density-matrix equation in a low spin-polarization limit, we obtain explicit formulas describing the role of spin-exchange collisions in the interactions between atoms and magnetic fields, especially the nonresonant radio-frequency fields, which are widely used to manipulate atoms. The results derived from these equations agree well with density-matrix simulations and previous experimental results, and provide a simple and precise way to quantitatively analyze the effect of spin-exchange collisions on atoms. Our paper is helpful to gain physical insight into the spin-exchange collisions and optimize the performance of atom-based precision measurement instruments.

We report an all-optical atomic vector magnetometer using dual Bell-Bloom optical pumping beams in a Rb vapor cell. This vector magnetometer consists of two orthogonal optical pumping beams, with amplitude modulations at ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb}$ Larmor frequencies, respectively. We simultaneously detect atomic signals excited by these two pumping beams using a single probe beam in the third direction, and extract the field orientation information using the phase delays between the modulated atomic signals and the driving beams. By adding a Herriott cavity inside the vapor cell, we improve the magnetometer sensitivity. We study the performance of this vector magnetometer in a magnetic field ranging from 100 mG to 500 mG, and demonstrate a field angle sensitivity better than 10 $\mu \mathrm{rad}/{\mathrm{Hz}}^{1/2}$ above 10 Hz.

We demonstrate a single-beam three-axis parametric-resonance magnetometer operated in near-zero fields. By reflecting the incident laser beam at 90° in the vapor cell and applying three orthogonal parametric modulation fields, the three components of the magnetic field can be extracted from the transmitted light signal. Our vector magnetometer experimentally demonstrates magnetic-field sensitivities of 30 fT Hz^−1/2 along x- and y-axes and 70 fT Hz^−1/2 along the z-axis, and features a compact single-beam architecture, which is particularly attractive for applications requiring highly sensitive measurements of the vector components of magnetic fields with low power consumption and miniaturized magnetometers, such as magnetoencephalography and magnetocardiography.