Heterodyne broadband detection of axion dark matter

We propose a new broadband search strategy for ultralight axion dark matter that interacts with electromagnetism. An oscillating axion field induces transitions between two quasidegenerate resonant modes of a superconducting cavity. In two broadband runs optimized for high and low masses, this setup can probe unexplored parameter space for axionlike particles covering 15 orders of magnitude in mass, including astrophysically long-ranged fuzzy dark matter.