Constraining meV Axion Dark Matter with ALMA Observations of the Galactic Center Magnetar SGR 1745-2900

We report a mm-wave search for axion dark matter from SGR 1745-2900, based on 4.8 h of ALMA observations. No candidate features are found between 133.99-135.78, 135.91-137.70, 145.99-147.78, and 147.99-149.78~GHz, corresponding to 0.55-0.62 meV. Interpreting this null result within a state-of-the-art stellar framework, we derive sensitivity to the axion-photon coupling at the level of $g_{\gamma}\gtrsim 2\times10^{-11}$ GeV$^{-1}$ under a standard Navarro-Frenk-White profile; down to $g_{\gamma}\gtrsim 2\times10^{-13}$ GeV$^{-1}$ upon accounting for a dense dark-matter spike around Sagittarius A*, probing the quantum chromodynamics axion parameter space.