  Gravitational atoms produced from the superradiant extraction of rotational
energy of spinning black holes can reach energy densities significantly higher
than that of dark matter, turning black holes into powerful potential detectors
for ultralight bosons. These structures are formed by coherently oscillating
bosons, which induce oscillating metric perturbations deflecting photon
geodesics passing through their interior. The deviation of nearby geodesics can
be further amplified near critical bound photon orbits. We discuss the prospect
of detecting this deflection using photon ring autocorrelations with the Event
Horizon Telescope and its next-generation upgrade, which can probe a large
unexplored region of the cloud mass parameter space when compared with previous
constraints.
