Calibration of a single-atom detector for atomic microchips

We experimentally investigate a scheme for detecting single atoms magnetically trapped on an atom chip. The detector is based on the photoionization of atoms and the subsequent detection of the generated ions. We describe the characterization of the ion detector with emphasis on its calibration via the correlation of ions with simultaneously generated electrons. A detection efficiency of 47.8±2.6% is measured, which is useful for single-atom detection, and close to the limit allowing atom counting with sub-Poissonian uncertainty.