Rydberg Series Excitation of a Single Trapped

A complete set of spectroscopic data is indispensable when using Rydberg states of trapped ions for quantum information processing. We carried out Rydberg series spectroscopy for nS_{1/2} states with 38≤n≤65 and for nD_{5/2} states with 37≤n≤50 on a single trapped ^{40}Ca^{+} ion. We determined the ionization energy of 2 870 575.582(15) GHz, 60 times more accurately as compared to the accepted value and contradicting it by 7.5 standard deviations. We confirm quantum defect values of δ_{S_{1/2}}=1.802 995(5) and δ_{D_{5/2}}=0.626 888(9) for nS_{1/2} and nD_{5/2} states, respectively, which allow for unambiguous addressing of Rydberg levels of Ca^{+} ions. Our measurements confirm Rydberg ion scaling properties, e.g., for blackbody induced ionization, linewidths and excitation strengths.