Optical frequency standards with trapped laser-cooled ions
Dr. Ekkehard Peik (Physikalisch-Technische Bundesanstalt, Braunschweig)

Optical frequency standards based on forbidden transitions of trapped and laser-cooled ions have now achieved higher stability and greater accuracy than primary cesium clocks. We investigate an optical clock based on the 171Yb+ ion. This ions possesses two suitable reference transitions: the electric quadrupole transition S1/2 – D3/2 at 436 nm and the extremely narrow electric octupole transition S1/2 - F7/2 at 467 nm. The ratio of these transition frequencies can be measured as a dimensionless number with a femtosecond laser frequency comb, allowing precise evaluation of systematic uncertainty contributions and a sensitive search for temporal variations of the fine structure constant. We are preparing nuclear laser spectroscopy of the 7.6 eV transition between the two lowest states of the Th-229 nucleus in trapped thorium ions. We have developed concepts for a highly accurate nuclear clock based on this transition and describe first steps towards the experimental realization.