The geomagnetic field encompasses a range of phenomena, from the slowly evolving main magnetic field over decades to the rapidly changing resonances of the Earth-ionosphere cavity, known as Schumann resonances (SRs), which oscillate at tens of cycles per second. Typically, the proportion of these components in the geomagnetic field is inversely related to their frequency. However, the rapidly changing components carry rich, real-time information about the Earth's spatial environment. In this work, we introduce a type of magnetometer, the finite-field alkali-noble-gas spin (FANS) magnetometer, designed to measure these weak signals with high sensitivity against geomagnetic background disturbances. The FANS magnetometer consists of two main components: a spin-based amplifier and an alkali-metal atomic magnetometer. The spin-based amplifier can amplify weak magnetic fields at specific frequencies by up to 70 times using highly polarized noble-gas spins. Furthermore, the alkali-metal atomic magnetometer is employed to measure the amplified signal and to provide a stable resonance field for the spin-based amplifier via a feedback system. We demonstrate a noise floor of $\sim 10{\text{fT/Hz}}^{1/2}$ while measuring simulated SR magnetic signals, effectively reducing common interference from the Earth's magnetic field. The FANS magnetometer exhibits remarkable anti-interference capabilities and provides a powerful tool to investigate geomagnetic physics.

Close

PrevNext

View figure in article

• Atomic & molecular processes in external fields
• Nuclear & electron resonance
• Optical pumping