August 14, 2024 -- A research team led by Prof PENG Xinhua and Associate Prof. JIANG Min from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) has discovered the Fano resonance interference effect between mixed atomic spins. They proposed a novel magnetic noise suppression technique, reducing magnetic noise interference by at least two orders of magnitude. The study was published in Physical Review Letters.

In the past few decades, exotic spin interactions beyond the standard model of particle physics have attracted widespread attention in the field of precision measurement. These exotic spin interactions cover many frontier areas, such as searching for spin-dark matter particle interactions, the fifth force, etc. In these precision experiments, exotic interactions are equivalent to magnetic fields acting on spins, and extremely weak magnetic field measurement techniques provide a new means for testing such weak magnetic field signals.

However, the magnetic field signals in these studies are extremely weak and often masked by noise backgrounds, especially susceptible to interference such as magnetic noise. Although atomic comagnetometers can use two different spins to reduce the effects of magnetic field drift and fluctuations, previous atomic comagnetometers have only been effective for low-frequency magnetic noise (less than 1Hz), which severely hinders the experimental search for exotic spin interactions in a vast unexplored parameter space.

The research team has developed a magnetic noise suppression method based on magnetic noise self-compensation effects, and experimentally verified it in a mixed system of potassium (K) and 3He gases. In this system, K polarized by lasers served as a means of polarization and readout for the nuclear spin of 3He, achieving their polarization through spin-exchange collisions.

In previous experiments, the bias magnetic field was typically set to be equal in magnitude but opposite in direction to the equivalent field produced by He atoms. The nuclear spin of He could adiabatically follow the external low-frequency magnetic noise, thereby achieving suppression effects. Researchers found that while changing the magnitude of the bias field, effective suppression of higher frequency magnetic noise can be achieved by adjusting the angle between the detection direction and the external specific frequency magnetic noise.

Moreover, this approach provided a complete and accurate theoretical explanation for the experimental phenomenon from a new perspective of Fabry-Perot resonance interference cancellation. Researchers have demonstrated the suppression of magnetic noise from near direct current to up to 200Hz using the self-compensation effect of magnetic noise, with the suppression multiples all exceeding 2 orders of magnitude.

This work further indicated that, if the sensitivity of magnetic detection was limited, utilizing this self-compensation effect of magnetic noise was expected to enhance the sensitivity to pseudomagnetic field by an order of magnitude. In other words, it reached a level of 0.1fT/Hz1/2 over a broader frequency range. The study will benefit areas such as dark matter detection and exotic spin interactions in fundamental physics research.