An ultra-broadband axion dark matter experiment

TL;DR

This paper introduces a broadband axion dark matter detection method using a dc SQUID at the flux sweet spot, achieving ultra-wide mass range sensitivity and surpassing current bounds.

Contribution

It presents a practical implementation leveraging quadratic flux dependence and lock-in modulation for broadband axion searches with improved sensitivity.

Findings

Sensitivity of |g_{aγγ}| ≳ 10^{-16} GeV^{-1}

Spans over 15 orders of magnitude in axion mass

Proposes background reduction and adaptation to other dark matter candidates

Abstract

We propose a novel broadband strategy to search for axions by leveraging observables controlled by the axion field squared. We present a practical implementation of this concept for probing the axion--photon coupling. This is done by operating a dc SQUID at the flux sweet spot, where the voltage depends quadratically on the magnetic flux, and using lock-in modulation to evade low-frequency noise. The proposed setup is ultra-broadband, spanning over 15 orders of magnitude in axion mass, with further expansion of the mass range possible. The projected sensitivity is $|g_{a\gamma\gamma}| \gtrsim 10^{-16} \text{ GeV}^{-1}$, orders of magnitude better than current bounds, and largely independent of axion mass. We discuss the sources of systematic background and a nulling technique to reduce them to an acceptable level. We also discuss how our strategy could be adapted to probe the axion-fermion coupling, as well as to detect other dark matter candidates such as dark photons.