| Abstract | This work examines the current status of research on optical frequency standards based upon single trapped ions. Methods for the containment and laser cooling of such single-ion samples are briefly discussed. Detection of ultra-narrow reference transitions via the observation of quantum jumps is outlined, together with the progress in the development of laser sources to provide cooling, detection and probing for such standards. A brief discussion on methods employed to date on stabilization to single-ion transition resonances is given, together with a summary of some of the principal sources for systematic shifts in such systems. Progress in the investigation of Ba⁺, Sr⁺, Ca⁺, Hg⁺, Yb⁺, and In⁺ single-ion reference transitions is given. The work concludes with an overview of the progress in the measurement of single-ion referenced optical frequency relative to the Cs realization of the SI second and other reference standards. |
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