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Abstract

A method to prepare arbitrary stored ions with low energy in the mK range would improve many high-precision Penning trap experiments and is essential for high-precision measurements of the antiproton and proton g-factors. In this thesis, we investigate sympathetic cooling of a single individually-trapped proton by laser-cooled 9Be+ ions stored in a separate trap. Both ions are coupled by image currents induced in a common electrode and the coupling is enhanced by a connected cryogenic superconducting radio-frequency RLC oscillator. The image-current based coupling makes the technique applicable to arbitrary ions. We describe the new experimental setup, based on a significant modification of the previous proton g-factor experiment, and the installation and optimization of new image-current detectors. We further describe the development and characterization of a single-photon sensitive fluorescence detection system based on silicon photomultipliers integrated into the cryogenic Penning trap. We demonstrate laser-cooling of the 9Be+ ions and measure their temperature to 1.1(2) mK using fluorescence detection. The simultaneous detection of fluorescence photons and image currents of laser-cooled 9Be+ ions enables a measurement of the laser-induced damping. We further demonstrate sympathetic cooling of the axial mode of a single proton to 2.6(2.5) K, limited by the applied temperature measurement method. With a newly developed temperature measurement trap, we improve this value to 160(30) mK, almost two orders of magnitude below the environment temperature. Finally, we argue that the technique can be optimized to reach temperatures in the low double-digit mK range, which would enable a future generation of antiproton and proton g-factor measurements with an order of magnitude improved precision. For other high-precision Penning trap experiments, the method will be an attractive tool to prepare arbitrary ions for measurement.