Axion dark matter detection by superconducting resonant frequency conversion

We propose an approach to search for axion dark matter with a specially designed superconducting radio frequency cavity, targeting axions with masses ma ≲ 10⁻⁶ eV. Our approach exploits axion-induced transitions between nearly degenerate resonant modes of frequency ~ GHz. A scan over axion mass is achieved by varying the frequency splitting between the two modes. Compared to traditional approaches, this allows for parametrically enhanced signal power for axions lighter than a GHz. The projected sensitivity covers unexplored parameter space for QCD axion dark matter for 10⁻⁸ eV ≲ ma ≲ 10⁻⁶ eV and axion-like particle dark matter as light as ma~ 10⁻¹⁴ eV.