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Originally published in Science Express on 12 July 2001
Science 3 August 2001:
Vol. 293. no. 5531, pp. 825 - 828
DOI: 10.1126/science.1061171
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Research Articles

An Optical Clock Based on a Single Trapped 199Hg+ Ion

S. A. Diddams,1* Th. Udem,1dagger J. C. Bergquist,1 E. A. Curtis,12 R. E. Drullinger,1 L. Hollberg,1 W. M. Itano,1 W. D. Lee,1 C. W. Oates,1 K. R. Vogel,1 D. J. Wineland1

Microwave atomic clocks have been the de facto standards for precision time and frequency metrology over the past 50 years, finding widespread use in basic scientific studies, communications, and navigation. However, with its higher operating frequency, an atomic clock based on an optical transition can be much more stable. We demonstrate an all-optical atomic clock referenced to the 1.064-petahertz transition of a single trapped 199Hg+ ion. A clockwork based on a mode-locked femtosecond laser provides output pulses at a 1-gigahertz rate that are phase-coherently locked to the optical frequency. By comparison to a laser-cooled calcium optical standard, an upper limit for the fractional frequency instability of 7 × 10-15 is measured in 1 second of averaging--a value substantially better than that of the world's best microwave atomic clocks.

1 Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80305, USA.
2 Department of Physics, University of Colorado, Boulder, CO 80309, USA.
*   To whom correspondence should be addressed. E-mail: sdiddams{at}boulder.nist.gov

dagger    Present address: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann Strasse 1, 85748, Garching, Germany.

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