  Ultralight bosonic dark matter (UBDM) can be described by a classical
wave-like field oscillating near the Compton frequency of the bosons. If a
measurement scheme for the direct detection of UBDM interactions is sensitive
to a signature quadratic in the field, then there is a near-zero-frequency (dc)
component of the signal. Thus, a detector with a given finite bandwidth can be
used to search for bosons with Compton frequencies many orders of magnitude
larger than its bandwidth. This opens the possibility of a detection scheme
analogous to Hanbury Brown and Twiss intensity interferometry. Assuming that
the UBDM is virialized in the galactic gravitational potential, the random
velocities produce slight deviations from the Compton frequency. These result
in stochastic fluctuations of the intensity on a time scale determined by the
spread in kinetic energies. In order to mitigate ubiquitous local low-frequency
noise, a network of sensors can be used to search for the stochastic intensity
fluctuations by measuring cross-correlation between the sensors. This method is
inherently broadband, since a large range of Compton frequencies will yield
near-zero-frequency components within the sensor bandwidth that can be searched
for simultaneously. Measurements with existing sensor networks have sufficient
sensitivity to search experimentally unexplored parameter space.
