Intensity interferometry for ultralight bosonic dark matter detection
  Ultralight bosonic dark matter (UBDM) can be described by a classical
wave-like field oscillating at 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 interferometry. Assuming that the UBDM is
virialized in the gravitational potential, for example of the Milky Way, 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 velocities. 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 have a near-zero-frequency component within the sensor
bandwidth that can be searched for simultaneously. Experiments with existing
clock and magnetometer networks have sufficient sensitivity to search a broad
range of unexplored parameter space.
