Building instructions for a ferromagnetic axion haloscope

Abstract

A ferromagnetic haloscope is a rf spin magnetometer used for searching dark matter in the form of axions. A magnetic material is monitored searching for anomalous magnetization oscillations which can be induced by dark matter axions. To properly devise such instrument, one first needs to understand the features of the searched-for signal, namely the effective rf field of dark matter axions \(B_\mathrm{{a}}\) acting on electronic spins. Once the properties of \(B_\mathrm{{a}}\) are defined, the design and test of the apparatus may start. The optimal sample is a narrow linewidth and high spin-density material such as yttrium-iron garnet, coupled to a microwave cavity with almost matched linewidth to collect the signal. The power in the resonator is collected with an antenna and amplified with a Josephson parametric amplifier, a quantum-limited device which, however, adds most of the setup noise. The signal is further amplified with low-noise HEMT and down-converted for storage with an heterodyne receiver. This work describes how to build such apparatus, with all the experimental details, the main issues one might face, and some solutions.