http://www.nature.com/news/2007/071114/full/news.2007.242.html#B1

A measurement has been made on a quantum system at the greatest precision theoretically possible, according to a paper published today in Nature 1.

The team, led by Geoff Pryde of Griffith University in Brisbane, Australia, has managed to measure the interference between two light waves as they beat slightly out of step, with a precision that is limited only by Heisenberg’s uncertainty principle, the most fundamental and unavoidable source of ‘fuzziness’ in the quantum world.
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Here is a link to the actual nature article, if anyone has subscriptions.