Muonium Spectroscopy as a Quantum Sensor for Ultralight Axion Dark Matter

High-intensity muon beams could enable a muonium-based search for ultralight axions through resonant quantum transitions between hyperfine states. Combining theoretical calculations with simulation results, we demonstrate that such a muonium-based experimental approach -exemplified by one of the facilities under development in Huizhou- could improve constraints on the axion-muon coupling by up to two orders of magnitude compared with existing limits from the muon g-2 measurement, over the axion mass range of $10^{-15}$ eV to $10^{-12}$ eV. These results establish muonium spectroscopy as a powerful probe of physics beyond the Standard Model.