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Science 6 December 2002:
Vol. 298. no. 5600, p. 1849
DOI: 10.1126/science.298.5600.1849a
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Editors' Choice: Highlights of the recent literature

Modern watches keep time by counting the vibrations of a quartz crystal. In a similar manner, atomic clocks keep time by counting the vibrations of excited cesium atoms. As a rule, the stability of a clock is expected to improve as the frequency used to keep time increases. Just as most watches drift off and need to be reset occasionally, so too do atomic clocks, albeit on much longer time scales and with much smaller adjustments. The key to improved timekeeping is to use a frequency standard that is stable. Wilpers et al. show that using a cold ensemble of neutral calcium atoms as the frequency standard provides superior stability and comparable accuracy to the best single ion traps and microwave standards currently available. -- ISO

Phys. Rev. Lett. 89, 230801 (2002).

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Science. ISSN 0036-8075 (print), 1095-9203 (online)