Measurement of the separation between atoms beyond diffraction limit
  Precision measurement of small separations between two atoms or molecules has been of interest since the early days of science. Here, we discuss a scheme which yields spatial information on a system of two identical atoms placed in a standing wave laser field. The information is extracted from the collective resonance fluorescence spectrum, relying entirely on far-field imaging techniques. Both the interatomic separation and the positions of the two particles can be measured with fractional-wavelength precision over a wide range of distances from bout lambda/550 to lambda/2. 
Jun-Tao Chang, Joerg Evers, Marlan O. Scully, and M. Suhail Zubairy