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