Stringent Constraints on Spin-Spin-Velocity-Dependent Exotic Interactions with a Levitated Magnet Force Sensor.

Exotic spin-spin-velocity-dependent interactions, predicted in extensions of the standard model involving new bosonic fields, could resolve fundamental puzzles from dark matter to cosmic asymmetry. However, exploring these weak potential interactions at centimeter scales presents formidable challenges, primarily due to the overwhelming dominance of electromagnetic backgrounds that can easily obscure the weak exotic signals. Here, we utilize a levitated magnet force sensor with ultrahigh electron spin density to probe these interactions. We constrain two interactions individually through a designed spin source and a multilayer magnetic shielding system that suppresses electromagnetic backgrounds. In this Letter, we constrain two types of interactions: the V_{6} potential at force ranges from 10^{-3} to 6×10^{-2}  m and the V_{14} potential at ranges greater than 10^{-3}  m. Our measurements establish 95% confidence-level bounds of |f_{6}|≤2.12×10^{-13} and |f_{14}|≤2.34×10^{-23} at λ=1.6×10^{-2}  m, improving prior limits by up to 12 and 13 orders of magnitude, respectively. Our result demonstrates the levitated magnet as a highly sensitive probe for detecting new bosonic fields in extensions of the standard model.