  A model of photo-detection using a Bose--Einstein condensate in an atom-chip
based micro trap is analyzed. Atoms absorb photons from the incident light
field, receive part of the photon momentum and leave the trap potential. Upon
counting of escaped atoms within predetermined time intervals, the photon
statistics of the incident light is mapped onto the atom-count statistics.
Whereas traditional photo-detection theory treats the emission centers of photo
electrons as distinguishable, here the centers of escaping atoms are condensed
and thus indistinguishable atoms. From this an enhancement of the photon-number
resolution as compared to the commonly known counting formula is derived.
