Better atomic clocks herald new era of timekeeping

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Science  02 Mar 2018:
Vol. 359, Issue 6379, pp. 968
DOI: 10.1126/science.359.6379.968

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The atomic clocks that mark official time lose the equivalent of just 1 second every 200 million years. But metrologists are not satisfied. A more precise time standard might improve the navigation of spacecraft and help experimenters look for variations in fundamental constants that would signal new physics. So the push is on to replace current clocks, which are tuned to a specific microwave frequency, with even better clocks that exploit higher-frequency visible light. In a paper out last month, a group of experts set up by the International Bureau of Weights and Measures in Sèvres, France, lays out a road map for the steps needed to redefine the unit of time—the metric second—in terms of optical radiation. Already, physicists at the National Institute of Standards and Technology Boulder Laboratories in Colorado appear to have satisfied one of the road map's key requirements—a 100-fold improvement in accuracy over the best microwave clocks—using a pair of optical clocks.