Spin-amplification SERF atomic magnetometer based on direct feedback

We demonstrate that atomic spin trajectories on the Bloch sphere can be manipulated through direct feedback, achieving spin amplification. This method is applied to Spin-Exchange Relaxation-Free (SERF) magnetometers where a feedback loop introduces a magnetic field positively proportional to the transverse spin polarization, which significantly amplifies the low-frequency response signal by an order of magnitude. Experimental results show that the feedback mechanism improves the signal-to-noise ratio and effectively strengthens the system’s ability to suppress technical noise. In addition, this feedback-enabled magnetometer exhibits superior sensitivity at lower spin polarization, reducing reliance on optical power and thereby facilitating scalability in multi-channel systems. This approach can be extended to various physical systems utilizing atomic spins, such as quantum memory and quantum metrology.