Rydberg excitation of trapped ions
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Abstract
In this thesis I describe the excitation of trapped 40Ca+ ions to Rydberg states. For the first time, the excellent experimental control over single ions in Paul traps has been combined with the unique features of highly excited Rydberg states, establishing a novel platform for experimental quantum computing and quantum simulation.
Due to the doubly charged core, and the correspondingly increased binding energy, Rydberg excitation of ions requires vacuum ultraviolet (VUV) light for single-photon excitation
or multi-photon excitation with ultraviolet (UV) radiation. For the experimental
work presented in this thesis, we have chosen single-photon excitation with VUV radiation near 122nm wavelength. We have designed and built an ion trap apparatus consisting of an ultra high vacuum setup, laser sources with wavelengths in the visible and infrared spectrum, control electronics and a Paul trap and joined it with a preexisting source for continuous wave, coherent VUV radiation near 122nm wavelength. Characterization measurements of the joined apparatus have been performed. Particularly important is the
characterization of the VUV beam inside the ion trap, the compensation of residual electric fields at the ion crystal and the effects of the highly energetic VUV photons on ion trap operation. With the joined system we have successfully demonstrated photo-ionization of trapped and cold 40Ca+ ions.
After the presentation of this preparatory work, I describe the excitation of trapped 40Ca+ ions to Rydberg states. From the initial metastable 3D states, we have excited ions to the Rydberg states 22F, 52F, 53F and 66F with light at wavelengths near 123 nm and 122 nm. Excitation wavelengths have been measured as 123.256 119(5) nm (3D5/2 → 22F), 122.041 913(5) nm (3D3/2 → 52F), 122.032 384(10) nm (3D3/2 → 53F) and 122.040 50(5) nm (3D5/2 → 66F). From these wavelengths, principle quantum numbers, quantum defect and consequently the angular momentum state of the excited states have been
determined. We investigated the line shapes of the transitions to the highly sensitive Rydberg states in the oscillating potential of the Paul trap. Advanced techniques like coherent state preparation of the ion in the initial 3D5/2 state and the addressed Rydberg excitation of single ions in one dimensional ion strings have been realized. The work presented in this dissertation paves the way towards Rydberg quantum logic applications with trapped ions.