Testing Fundamental Symmetries with Trapped Single Ions

Spectroscopy on trapped ions enables sensitive searches for indications of New Physics beyond the present Standard Model of Particle Physics. Quantum optics has a number of methods and techniques that can be most successfully applied for obtaining most reliable results from such research. Ions with a single valence electron such as the heavy alkali earth ion Ba+ and Ra+ are particularly suited, because for such system the necessary atomic theory calculations can be performed with sufficiently high accuracy [1]. In experiments utmost precision is necessary to enable the extraction of New Physics effects from comparing precisely measured and calculated values. An example for such searches for Physics Beyond the Standard Model is the measurement of the weak interaction in Ba+ and Ra+. The sensitivity to the Weinberg angle ( sin2Ɵw) in Ra+ is some 50 times larger than in Ba+. Since there are only radioactive isotopes of Ra, all necessary techniques can be developed using Ba. The measurement of a reliable value for sin2Ɵw requires that atomic wave functions in the atoms are known to sufficient accuracy. Therefore we perform atomic spectroscopy on different isotopes of Ba +and Ra+. We have performed absolute frequency measurements for Ba+ ions and we have precisely determined the 6s2S1/2 - 6p2P1/2, 6p2P1/2 - 5d2D3/2, 6s2S1/2 - 5d2D5/2 transition frequencies with more than 100 times improved accuracy using a single trapped 138Ba+ion and a frequency comb and I2 line locked laser system. We reached 10−11 relative accuracy [2]. Other isotopes are being measured at this time. Further we have determined the lifetime of the 52D5/2 state to be significantly shorter than previously reported, leaving an open puzzle at present [3]. Such measurements test the wave functions at larger distances from the nucleus. Measurements of hyperfine structures investigate the atomic wave functions near the origin. We have performed therefore hyperfine structure measurements in a number of trapped, short-lived Ra isotopes [4]. With isotope shift measurements we have verified the consistency of calculations and theory in Ra+ [5]. We note that precision measurements of weak interaction effects in single ions are very closely related to the development of single ion optical clocks [6].