Limit to minimally destructive optical detection of atoms

The optical techniques used for investigating the properties of Bose-Einstein condensates based on dispersion and absorption, which can be described by a two-level atom were studied. Both the phenomena were shown to lead to spontaneous emission that is destructive at the low energies involved with ultracold atomic systems. Both the phenomena were also shown to lead to the same limit to the signal to noise ratio for a given destruction. A method for calculating the phase shift of a laser beam was developed. It was shown that no single-pass optical technique using classical light and a three-level atom can exceed this limit.