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Lattice trap improves optical clocks

20 May 2005

A clever way to trap atoms improves the accuracy of optical clocks, say Japanese researchers in this week’s Nature.

Researchers in Japan have come up with a way to optically trap neutral atoms which they say could push the boundaries of timekeeping. Unveiled in this week’s Nature, the team believes the high stability of its scheme could lead to timekeeping that is accurate to the 10-18 level. (Nature 435 321)

The gold standard in timekeeping is currently the caesium-133 atomic clock, which is accurate to 1 part in 10-15 and is used to define the fundamental unit of the time, the second.

Optical clocks, based on either single trapped-ions or cooled neutral atoms, are a promising successor to the atomic clock but are hard to stabilize. But this could be about to change thanks to work being carried out by Hidetoshi Katori and his colleagues from the University of Tokyo and the National Metrology Institute of Japan in Ibaraki.

By trapping a cloud of 10,000 cold (2 µK) strontium atoms in a so-called optical lattice (a special interference pattern formed by lasers), the Japanese team says it has created a highly stable optical clock with an oscillator frequency of 429 THz.

“Our optical lattice clock demonstrates a linewidth that is one order of magnitude narrower than that observed for neutral atom optical clocks and its stability is better than single ion clocks,” say the researchers in their Nature paper.

The lattice trapping enhances the clock's stability by preventing troublesome collisions between the atoms that plague traditional neutral atom clocks. At the same time the large number of atoms gives a much stronger signal than single ion clocks which emit a weak signal that needs to be averaged over a long time period.

Katori and colleagues use a Ti:sapphire laser emitting at 813.4 nm to trap their strontium atoms. The beam is reflected back on itself by a mirror and the atoms are trapped in the crests of the standing wave that forms the 1D optical lattice.

Jacqueline Hewett is technology editor on Optics.org and Opto & Laser Europe magazine.

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