  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.
