Constraining axion-like dark matter with a radio-frequency atomic magnetometer

TL;DR

This paper presents a broadband search for axion-like particles using a radio-frequency atomic magnetometer, setting new limits on their interactions with fermions in an unexplored mass range.

Contribution

It introduces a novel broadband detection method with a magnetometer to constrain ALP interactions, extending the search into a new dark matter mass range.

Findings

No significant ALP signals detected.

Set new upper limits on ALP-proton coupling $g_{\alpha pp}$.

Limits on $g_{\alpha nn}$ and $g_{\alpha ee}$ complement existing bounds.

Abstract

We report on a broadband search for axion-like-particle (ALP) interactions using a radio-frequency-operated $^{87}\mathrm{Rb}$ atomic magnetometer. The instrument provides wide spectral coverage and sensitivity to an oscillating pseudomagnetic field that may be generated by the gradient coupling of the ALP field to the constituent fermions of atoms. We search for an ALP-gradient signature in the mass range $2.40\times10^{-10}\,\mathrm{eV}/c^{2}$--$2.11\times10^{-9}\,\mathrm{eV}/c^{2}$. No statistically significant signatures of an oscillating magnetic field are observed, and we derive upper limits on the corresponding ALP-proton, -neutron and -electron couplings, $g_{\alpha pp}$, $g_{\alpha nn}$ and $g_{\alpha ee}$, respectively. The result on $g_{\alpha pp}$ improves over previous laboratory searches, while the limits on $g_{\alpha nn}$ and $g_{\alpha ee}$ complement earlier laboratory searches and astrophysical bounds. The work extends searches for ALP-fermion interactions into a mass region largely unexplored in a dark-matter context, demonstrating the potential of our method for broadband axion-like particle searches targeting the Galactic dark-matter halo.