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Forbidden transitions in single laser-cooled trapped ions provide highly stable and accurate references for optical frequency standards. This paper describes recent progress on strontium and ytterbium ion optical frequency standards under development at NPL.
The frequency of the 2S1/2 (F = 0) - 2 F7/2(F = 3, mF = 0) transition in a single, trapped, laser cooled ion of 171Yb+ has been measured with a femtosecond laser frequency comb generator. The uncertainty is limited by measurement statistics and by the AC Stark shift
Summary form only given. A single laser-cooled ion held in an electrodynamic trap is a near ideal atomic sample for a frequency standard. The quantum jump technique is used to observe a high-Q forbidden transition in the ion. It has been suggested that the ultimate limit to the reproducibility of a standard of this type will lie in the region of one part in 10/sup 18/.
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