Search for Exotic Long-Range Spin-Dependent Interactions with Dressed Atoms

Landé factor quantifies particle responses to magnetic fields, and is an essential parameter for quantum precision measurements. We propose a technique to actively manipulate the Landé factor based on the dressing effect of radio-frequency (rf) magnetic fields. We demonstrate a magnetic-field-insensitive system in which the frequency of the rf field is comparable to the spin-exchange (SE) rate of atoms, and the field strength is strong enough. Despite the system is insensitive to magnetic fields, it remains sensitive to exotic spin-dependent interactions. By utilizing magnetic-field-insensitive Zeeman resonances, we search for the non-magnetic long-range spin-dependent interaction V₉₊₁₀ of protons. The constraint on the long-range monopole-dipole interaction V₉₊₁₀ between protons of alkali-metal atoms and nucleons of the Earth is enhanced by an order of magnitude, reaching 4.2×10^-33. This method motivates a deeper understanding on the SE collision mechanism and offers a novel approach to search for spin-dependent interactions.