Ultralight dark matter detection with levitated ferromagnets

TL;DR

This paper explores how levitated ferromagnets can serve as sensitive detectors for ultralight dark matter, analyzing their response to AC magnetic fields to project their potential in detecting axion-like particles and dark photons.

Contribution

It introduces a novel approach to using levitated ferromagnets for dark matter detection by studying their AC response and projecting future sensitivities.

Findings

Existing setups have comparable sensitivity to axion-electron coupling as other experiments.

Future setups could probe ultralight dark matter with masses below 1 feV.

Levitated ferromagnets can detect multiple dark matter couplings with high precision.

Abstract

Levitated ferromagnets act as ultraprecise magnetometers, which can exhibit high quality factors due to their excellent isolation from the environment. These instruments can be utilized in searches for ultralight dark matter candidates, such as axionlike dark matter or dark-photon dark matter. In addition to being sensitive to an axion-photon coupling or kinetic mixing, which produce physical magnetic fields, ferromagnets are also sensitive to the effective magnetic field (or "axion wind") produced by an axion-electron coupling. While the dynamics of a levitated ferromagnet in response to a DC magnetic field have been well studied, all of these couplings would produce AC fields. In this work, we study the response of a ferromagnet to an applied AC magnetic field and use these results to project their sensitivity to axion and dark-photon dark matter. We pay special attention to the direction of motion induced by an applied AC field, in particular, whether it precesses around the applied field (similar to an electron spin) or librates in the plane of the field (similar to a compass needle). We show that existing levitated ferromagnet setups can already have comparable sensitivity to an axion-electron coupling as comagnetometer or torsion balance experiments. In addition, future setups can become sensitive probes of axion-electron coupling, dark-photon kinetic mixing, and axion-photon coupling, for ultralight dark matter masses $m_\mathrm{DM}\lesssim\mathrm{feV}$.