[time-nuts] Nature: Hyper-precise atomic clocks face off to redefine time

[Hal Murray]

Nice picture: A strontium-ion optical clock housed at the National Physical 
Laboratory in Teddington, UK.

Over the past decade, various laboratories have created prototype optical 
atomic clocks, which use different elements such as strontium and ytterbium 
that emit and absorb higher-frequency photons in the visible spectrum. This 
finer slicing of time should, in principle, make them more accurate: it is 
claimed that the best of these clocks gain or lose no more than one second 
every 15 billion years (1E18 seconds) -- longer than the current age of the 
Universe -- making them 100 times more precise than their caesium 
counterparts. Optical clocks are claimed to be the best timekeepers in 
existence, but the only way to verify this in practice is to compare 
different models against each other and see whether they agree.

Starting on 4 June, four European laboratories will kick off this testing 
process -- the National Physical Laboratory (NPL) in Teddington, UK; the 
department of Time-Space Reference Systems at the Paris Observatory; the 
German National Metrology Institute (PTB) in Braunschweig, Germany; and 
Italy's National Institute of Metrology Research in Turin. Between them, the 
labs host a variety of optical clocks that harness different elements in 
different experimental set-ups.


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