Cavity based high-fidelity and non-destructive single atom detection on an atom chip

In this thesis, we demonstrate the preparation and detection of single atoms on an atom chip. We prepare a single Rubidium atom strongly coupled to a high-finesse cavity integrated to the atom chip. The atom is extracted from a Bose-Einstein condensate and trapped at the maximum of the cavity field. The prepared system is reproducibly in the strong-coupling regime of cavity quantum electrodynamics, as shown by a measurement of the normal mode spectrum of the coupled system. We use the cavity reflection and transmission signal to infer the atomic hyperfine state with a fidelity exceeding 99.93% in a detection time of 100 microseconds. The atom remains trapped during the detection. This performance of the detector is comparable to the best ion-trap experiments and makes the detector suitable for error correcting schemes in the context of quantum information processing. Additionally, the cavity-based detection scheme greatly reduces scattering compared to optical detection schemes in free space. We measure the scattering rate during detection, and show that we are able to detect the atomic internal state with an error below 10% while scattering less than 0.2 photons on average. To finalize the characterization of the detection process, we analyze the projection of the atomic state due to the measurement by performing a quantum Zeno type experiment. We find that each photon incident on the cavity reduces the coherence of the atomic state by a factor of 0.7. The presented detection is close to the textbook example of a projective measurement of a two-level quantum system. (author)