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Henkel, Florian (2011): Photoionisation detection of single 87Rb-atoms using channel electron multipliers. Dissertation, LMU München: Fakultät für Physik



Fast and efficient detection of single atoms is a universal requirement concerning modern experiments in atom physics, quantum optics, and precision spectroscopy. In particular for future quantum information and quantum communication technologies, the efficient readout of qubit states encoded in single atoms or ions is an elementary prerequisite. The rapid development in the eld of quantum optics and atom optics in the recent years has enabled to prepare individual atoms as quantum memories or arrays of single atoms as qubit registers. With such systems, the implementation of quantum computation or quantum communication protocols seems feasible. This thesis describes a novel detection scheme which enables fast and efficient state analysis of single neutral atoms. The detection scheme is based on photoionisation and consists of two parts: the hyperfine-state selective photoionisation of single atoms and the registration of the generated photoion-electron pairs via two channel electron multipliers (CEMs). In this work, both parts were investigated in two separate experiments. For the first step, a photoionisation probability of p_ion = 0.991 within an ionisation time of t_ion = 386 ns is achieved for a single 87Rb-atom in an optical dipole trap. For the second part, a compact detection system for the ionisation fragments was developed consisting of two opposing CEM detectors. Measurements show that single neutral atoms can be detected via their ionisation fragments with a detection efficiency of eta_atom = 0.991 within a detection time of t_det = 415.5 ns. In a future combined setup, this will allow the state-selective readout of optically trapped, single neutral 87Rb-atoms via photoionisation detection with an estimated detection efficiency eta = 0.982 and a detection time of t_tot = 802 ns. Although initially developed for single 87Rb-atoms, the concept of photoionisation detection is in principle generally applicable to any atomic or molecular species. As efficient readout unit for single atoms or even ions, it might represent a considerable alternative to conventional detection methods due to the high optical access and the large sensitive volume of the CEM detection system. Additionally, its spatial selectivity makes it particularly suited for the readout of single atomic qubit sites in arrays of neutral atoms as required in future applications such as the quantum-repeater or quantum computation with neutral atoms. The obtained high detection efficiency eta and fast detection time t_tot of the new detection method fullfill the demanding detector requirements for a future loophole-free test of Bell's inequality under strict Einstein locality conditions using two optically trapped, entangled 87Rb-atoms at remote locations. In such a configuration, the locality and the detection loophole can be simultaneously closed in one experiment.