  Imaging using interferometer arrays based on the Van Cittert-Zernike theorem
has been widely used in astronomical observation. Recently it was shown that
superresolution can be achieved in this system for imaging two weak thermal
point sources. Using quantum estimation theory, we consider the fundamental
quantum limit of resolving the transverse separation of two strong thermal
point sources using interferometer arrays, and show that the resolution is not
limited by the longest baseline. We propose measurement techniques using linear
beam splitters and photon-number-resolving detection to achieve our bound. Our
results demonstrate that superresolution for resolving two thermal point
sources of any strength can be achieved in interferometer arrays.
