Two-photon amplitude interferometry for precision astrometry
  Improved quantum sensing of photon wave-functions could provide high
resolution observations in the optical benefiting numerous fields, including
general relativity, dark matter studies, and cosmology. It has been recently
proposed that stations in optical interferometers would not require a
phase-stable optical link if instead sources of quantum-mechanically entangled
pairs could be provided to them, potentially enabling hitherto prohibitively
long baselines. A new refinement of this idea is developed, in which two
photons from different sources are interfered at two separate and decoupled
stations, requiring only a slow classical information link between them. We
rigorously calculate the observables and contrast this new interferometric
technique with the Hanbury Brown & Twiss intensity interferometry. We argue
this technique could allow robust high-precision measurements of the relative
astrometry of the two sources. A basic calculation suggests that angular
precision on the order of 10 microarcsecond could be achieved in a single
night's observation of two bright stars.
