Femtotesla Atomic Magnetometer Employing Diffusion Optical Pumping to Search for Exotic Spin-Dependent Interactions

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  fT_{rms}/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 λ>0.7  mm at 1σ confidence. The limit is more than 3 orders of magnitude tighter than the previous constraints for the force range between 1  mm∼10  mm, and one order of magnitude tighter for the force range above 10 mm.

Constraints on Spin-Spin Velocity-Dependent Interactions

The existence of exotic spin-dependent forces may shine light on new physics beyond the standard model. We utilize two iron shielded SmCo_{5} electron-spin sources and two optically pumped magnetometers to search for exotic long-range spin-spin velocity-dependent force. The orientations of spin sources and magnetometers are optimized such that the exotic force is enhanced and common-mode noise is effectively subtracted. We set direct limit on proton-electron interaction in the force range from 1 cm to 1 km. Our experiment represents more than 10 orders of magnitude improvement than previous works.

Constraints on exotic spin-velocity-dependent interactions

Experimental searches for exotic spin-dependent forces are attracting a lot of attention because they allow to test theoretical extensions to the standard model. Here, we report an experimental search for possible exotic spin-dependent force, specifically spin-and-velocity-dependent forces, by using a K-Rb-²¹Ne co-magnetometer and a tungsten ring featuring a high nucleon density. Taking advantage of the high sensitivity of the co-magnetometer, the pseudomagnetic field from this exotic force is measured to be ≤7 aT. This sets limits on coupling constants for the neutron-nucleon and proton-nucleon interactions in the range of ≥0.1 m (mediator boson mass ≤2 μeV). The coupling constant limits are established to be [Formula: see text] and [Formula: see text], which are more than one order of magnitude tighter than astronomical and cosmological limits on the coupling between the new gauge boson such as Z' and standard model particles.