Hertz-level measurement of the optical clock frequency in a single 88Sr+ ion.
The frequency of the 5s 2S(1/2)-4d 2D(5/2) electric quadrupole clock transition in a single, trapped, laser-cooled 88Sr+ ion has been measured by using an optical frequency comb referenced to a cesium fountain primary frequency standard. The frequency of the transition is measured as 444,779,044,095,484.6 (1.5) hertz, with a fractional uncertainty within a factor of 3 of that of the cesium standard. Improvements required to obtain a cesium-limited frequency measurement are described and are expected to lead to a 88Sr+ optical clock with stability and reproducibility exceeding that of the primary cesium standard.
Margolis
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National Physical Laboratory (NPL), Teddington, Middlesex TW11 0LW, UK. helen.margolis@npl.co.uk
Barwood
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Huang
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Klein
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Lea
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Szymaniec
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Gill
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