Semiclassical Theory of Superresolution for Two Incoherent Optical Point   Sources
  Using a semiclassical model of photodetection with Poissonian noise and insights from quantum metrology, we prove that linear optics and photon counting can optimally estimate the separation between two incoherent point sources without regard to Rayleigh's criterion. The model is applicable to weak thermal or fluorescent sources as well as lasers. 
Mankei Tsang, Ranjith Nair, and Xiao-Ming Lu
quant-ph physics.optics