Collective response and noise of a levitated ferromagnet lattice for ultralight dark matter detection

TL;DR

This paper proposes a scalable levitated ferromagnet lattice detector for ultralight dark matter, analyzing its collective response, noise characteristics, and enhanced sensitivity over single ferromagnet setups.

Contribution

It develops a theoretical model of the collective lattice response including interactions and boundary effects, and demonstrates improved dark matter detection sensitivity.

Findings

Lattice response includes mode mixing and boundary effects.

Interaction effects cause a narrow blind zone due to thermal noise.

Projected sensitivities surpass single-ferromagnet detectors in multiple channels.

Abstract

Ultralight dark matter can induce weak oscillating magnetic-like signals and can therefore be searched for with precision magnetometry. Levitated ferromagnets provide a sensitive platform for such searches, but a single ferromagnet is limited in total polarized spin and readout performance. We investigate a levitated ferromagnet lattice as a scalable detector for ultralight dark matter. We develop a theoretical description of the collective lattice response in the fully trapped regime, incorporating dipole-dipole interactions, finite-size effects, and boundary-induced mode mixing. We further analyze the collective noise budget and show that interaction effects mainly produce a narrow blind zone through thermal-noise amplification, while away from this region, the lattice preserves favorable collective noise scaling. We then derive projected sensitivities to axion-electron, dark-photon, and axion-photon couplings. We find that the lattice improves the reach in all three channels relative to a single-ferromagnet detector, with an additional coherent signal enhancement in the axion-photon channel from the lattice-generated electromagnetic background.