Precise atomic clock may redefine time

@article{Ball2013PreciseAC,
  title={Precise atomic clock may redefine time},
  author={Philip Ball},
  journal={Nature},
  year={2013}
}
  • P. Ball
  • Published 9 July 2013
  • Physics
  • Nature
Device lays the groundwork for a new second. 
On-ground characterization of the cold atoms space clock PHARAO
This thesis presents the experimental results obtained during the development and the ground tests of the flight model of the cold atoms space clock PHARAO. PHARAO, the first Primary Frequency

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An optical lattice clock
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This work reports a different approach, in which atoms trapped in an optical lattice serve as quantum references, and the ‘optical lattice clock’ demonstrates a linewidth one order of magnitude narrower than that observed for neutral-atom optical clocks, and its stability is better than that of single-ion clocks.
Experimental realization of an optical second with strontium lattice clocks.
TLDR
An important step in the direction of a possible new definition of the second is presented, and two state-of-the-art strontium optical lattice clocks are proven to agree within their accuracy budget, with a total uncertainty of 1.5 × 10(-16).