Indium single ion optical frequency standard

A single laser cooled ion in a radiofrequency trap can serve as the basis for a highly stable optical frequency standard. We present recent results of our work on single indium ions, using the ¹S₀ to ³P₀ transition at 236.5 nm wave-length as the clock transition. This resonance has a linewidth of only 0.82 Hz where systematic shifts should be controllable on the mHz level. A single In⁺ ion is stored in a miniature Paul-Straubel trap and laser cooled to a temperature of about 100 μK. The clock transition is excited using a frequency quadrupled Nd:YAG laser. A fractional resolution of 1.3·10^-13 has been achieved so far (linewidth of 170 Hz at 1267 THz). The absolute frequency of the clock transition clock transition has been measured with an uncertainty of 2·10^-13 using a frequency chain and a methane-stabilized HeNe laser as a reference, that was calibrated with a cesium clock