Description
Precision measurement of magnetic fields has important applications in brain science, biomedicine, geomagnetic navigation, magnetic anomaly detection etc. Atomic magnetometers are currently the most sensitive tools for magnetic field measurement; however, most high-sensitivity atomic magnetometers are scalar ones that can only measure the magnitude of the field. Vector magnetometers are capable of measuring both the magnitude and the direction of magnetic fields, and therefore can provide more information about the orientation and location of the field source. Yet, due to constraints from the operating principles, most vector magnetometers cannot simultaneously meet the requirements of high sensitivity, real-time, high spatial resolution, single-laser-beam and room temperature for device applications. We demonstrate a room-temperature all-optical vector magnetometer and triaxial brain field sensing using atomic magnetometer based on Electromagnetically induced transparency (EIT) in rubidium vapor cell with anti-relaxation wall coating. Employing the neural-network-based decoding techniques, we achieve the magnetic field amplitude sensitivity of $16.33~\mathrm{fT/\sqrt{Hz}}$ and directional sensitivities of $0.015~\mathrm{mrad/\sqrt{Hz}}$ for polar angle and $0.032~\mathrm{mrad/\sqrt{Hz}}$ for azimuth angle for a magnetic field about $140~\mathrm{nT}$. We further employ the magnetometer to develop a triaxial magnetoencephalography prototype device, which can sense the brain magnetic field signal in three orthogonal directions of evoked responses from auditory stimulation. Our approach of machine learning assisted vector atomic magnetometry can be extended to high-sensitivity detection of vector geomagnetic field and anomaly magnetic field detection. Meanwhile, our prototype device provides an important technical foundation for room-temperature, non-invasive triaxial bio-magnetic-field measurements.
