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Still more accurate clocks (Forwarded)

Subject: Still more accurate clocks Forwarded
From: Andrew Yee
Date: Thu, 02 Mar 2006 12:50:11 -0500
Newsgroups: sci.astro
Observatoire de Paris
Paris, France

Contacts:
Pierre Lemonde, Observatoire de Paris, SYRTE
Tél: 33 1 40 51 22 24
Fax: 33 1 43 25 55 42

28 February 2006

Still more accurate clocks

Optical lattice clocks are based on the measurement of the frequency of an atomic transition, and are quite promising to be in the future among the most precise clocks. A team from Paris Observatory (SYRTE) has just eliminated an obstacle in the race to the precision, which lets hope to reach in the future an accuracy of 10**-18. In an article to Physical Review Letters, the team presents in details an experimental study on the most serious limitation for this new type of clocks.

Optical lattice clocks have recently opened the most promising route towards more accurate and stable frequency standards. But to improve the present accuracy of a few 10**-16 of the best atomic clocks, it was necessary to lift the most serious limitation.

These clocks consist in measuring the optical frequency corresponding to the transition between two atomic levels of 87Sr (Figure 1). The objective is to be able to control the transition frequency of 500 THz (5x10**14 Hz) to within one millihertz (10**-3 Hz), or 10**-18 in fractional units. To reach this level, the motions of the atoms must be totally under control.

This is done by tightly confining the atoms in an optical lattice which freezes the atomic motion (Figure 2). Such a trap however can significantly shift the transition frequency and thus severely affect the clock accuracy.

Previous studies have shown that this frequency shift can be cancelled to first order by adjusting the wavelength of the trapping laser. Given the required level of control however, effects of higher order must be considered and so far nobody had been able to conclude regarding these effects.

The experimental results published by A. Brusch and collaborators are the first study of these higher orders effects, which was achieved by operating the clock at an unprecedented laser intensity. This study shows that these effects are not a limitation for a future accuracy at the 10**-18 level.

Home page of the team Horloge optique à atomes froids de strontium Sr,
     http://opdaf1.obspm.fr/www/sr/le_strontium.html

Reference:

Anders Brusch, Rodolphe Le Targat, Xavier Baillard, Mathilde Fouché, Pierre Lemonde: 2006, Hyperpolarizability effects in a Sr optical lattice clock Physical Review Letters, in press.

IMAGE CAPTIONS:

[Figure 1:
http://www.obspm.fr/actual/nouvelle/mar06/clock-f1.jpg (34KB)]
The cloud of cold atoms of Srontium (Sr)

[Figure 2:
http://www.obspm.fr/actual/nouvelle/mar06/clock-f2.jpg (75KB)]
Optical lattice trapping the atoms

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