Role of BEC in atom interferometry What is the major advantage of using Bose-Einstein condensate in atom interferometry compared with other sources of atoms? Detectors measure population difference in two arms of the interferometer. I wonder what BEC has to offer compared with cold atom gases (which are not BEC)?
 A: It depends on the specifics of the experiment. For example, if the atoms are in a trapped interferometer (something still very much sort after in the atomic physics community) such that the trapped states are separated by some frequency, broadening of the transition line-width can occur due to slight differences in trap topology. A BEC will be confined to a smaller region about the trap bottom minimising the broadening compared to a thermal cloud. However, collisions and inter/intra interactions of the atoms are more likely with a BEC than a thermal cloud. If the atoms aren't in a trapped scheme and are just guided, thermal clouds will have greater dispersion along the guiding paths compared to a BEC, which reduces fringe visibility or the contrast.
The sensitivity of an interferometer is also inversely proportional to the square root (for uncorrelated atoms) of the number of atoms. To get to a BEC many atoms must be evaporatively removed from the initial thermal cloud, reducing the potential sensitivity compared to the thermal case with more atoms.
A BEC can also be viewed as a monochromatic mode, whilst the atom interferometer using a thermal cloud acts more like a white light interferometer.
A: BEC provides an excellent phase-coherent zero-momentum "pool", where momentum control is crucial for the atomic interferometer.
