  We demonstrate a robust fiber-optics-based fluorescence detector, fully
integrated on an atom chip, which detects single atoms propagating in a guide
with 66% efficiency. We characterize the detector performance and the atom flux
by analyzing the photon statistics. Near-perfect photon antibunching proves
that single atoms are detected, and allows us to study the second-order
intensity correlation function of the fluorescence over three orders of
magnitude in atomic density.
