Fault-tolerant and finite-error localization for point emitters within   the diffraction limit
  We implement an estimator for determining the separation between two incoherent point sources. This estimator relies on image inversion interferometry and when used with the appropriate data analytics, it yields an estimate of the separation with finite-error, even when the sources come arbitrarily close together. The experimental results show that the technique has a good tolerance to noise and misalignment, making it an interesting consideration for high resolution instruments. 
Tang Zong Sheng, Kadir Durak and Alexander Ling
physics.optics quant-ph