A Single-Atom Optical Clock and a Test of the Stability of Fundamental Constants

S. Bize, S.A. Diddams, U. Tanaka, C.E. Tanner, W.H. Oskay, T. Parker, R.E. Drullinger, T. Heavner, S.R. Jefferts, L. Hollberg, W.M. Itano, D.J. Wineland, and J.C.Bergquist

Time and Frequency Division, National Institute of Standards and Technology

Interest in the temporal stability of the fundamental constants has been revived by recent astronomical observations which suggest a variation of the fine structure constant a=2pe²/hc by a part in 10⁵ over 10¹⁰ years [1]. The repeated comparison of atomic frequency standards based upon distinct atomic transitions provides one of the most promising settings for laboratory tests in this area, due to the potentially high stability and accuracy of the standards [2,3]. We will present the results of measurements conducted over the course of two years that compare the frequency v_Hg of the ¹⁹⁹Hg^{+ 2}S_1/2 (F=0) – ²D_1/2 (F=2,m_F=0) optical transition to the SI second as realized at NIST. Since the NIST time scale is calibrated with a cesium fountain primary frequency standard [4], we are fundamentally measuring the ratio of v_Hg (≈ 10¹⁵ Hz) to the cesium ground-state hyperfine splitting v_Cs (≈ 9.2 Ghz). These measurements show better reproducibility than 10 Hz at v_Hg, and constrain any possible variation of the ratio v_Hg/v_Cs to ± 7^.10^-15 yr¹. We will discuss the implications of the present work as a constraint to present-day variations of the constants that determine the atomic transition frequencies. We further describe the current limitations to the accuracy of our measurement and methods by which we expect to reduce the overall systematic uncertainty.

References:

[1] J.K. Webb et al., Phys. Rev. Lett. 87, 091301 -1-4 (2001).
[2] J.D. Prestage et al., Phys. Rev. Lett. 74, 3511 (1995)
[3] S.A. Diddams et al., Science 293, 825 (2001)
[4] S.R. Jefferts et al., Metrologia 39, 321 (2002).

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