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Abstract

Single-atom optical clocks and fundamental constants

Although time is considered a fundamental concept by many physicists, and even though its unit of measure can be constructed from other physical constants, most often time serves as no more than an arbitrary parameter to describe the mechanics of motion. However, the pursuit of better time-keeping devices provides a natural means for studying various aspects of nature, including the fundamental constants and the interaction of radiation and matter. In recent years, several groups throughout the world have initiated research toward the development and systematic evaluation of frequency and time standards based on narrow optical transitions in laser-cooled atomic systems. I will discuss some of the key ingredients to the make-up and operation of single atom, optical clocks and why they offer higher stability and accuracy than the best clocks of today. I will then present some of the results obtained at NIST through comparative studies of the Hg+ single ion optical clock, the Al+ single ion optical clock and the Cs fountain, primary frequency standard (NIST-F1) [1-3]. The most recent frequency comparison between the Hg+ optical clock and NIST-F1 shows an uncertainty of ~910-16 limited by the integration time, and recent measurements of the frequency ratio between the Al+ and Hg+ standards show an overall uncertainty of several parts in 10-17. The extremely precise measurements of the frequency ratios of these clocks over time have begun to offer more stringent limits on any temporal variation of the fine structure constant  as well as other tests of general relativity. References: [1] W. H. Oskay, S. A. Diddams, E. A. Donley, T. M. Fortier, T. P. Heavner, L. Hollberg, W. M. Itano, S. R. Jefferts, M. J. Delaney, K. Kim, F. Levi, T. E. Parker, and J. C. Bergquist “Single-Atom Optical Clock with High Accuracy” PRL 97, 020801 (2006). [2] T. M. Fortier, N. Ashby, J. C. Bergquist, M. J. Delaney, S. A. Diddams, T. P. Heavner, L. Hollberg, W. M. Itano, S. R. Jefferts, K. Kim, F. Levi, L. Lorini, W. H. Oskay, T. E. Parker, J. Shirley, and J. E. Stalnaker “Precision Atomic Spectroscopy for Improved Limits on Variation of the Fine Structure Constant and Local Position Invariance”, PRL 98, 070801 (2007). [3] T. Rosenband, D. B. Hume, P. O. Schmidt, C. W. Chou, A. Brusch, L. Lorini, W. H. Oskay, R. E. Drullinger, T. M. Fortier, J. E. Stalnaker, S. A. Diddams, W. C. Swann, N. R. Newbury, W. M. Itano, D. J. Wineland, and J. C. Bergquist, "Frequency ratio of Al+ and Hg+ single-ion optical clocks; Metrology at the 17th decimal place," Science 319, 1808 - 1812 (2008).

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