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Ratio of the Al+ and Hg+ Optical Clock Frequencies to 17 Decimal Places



Wayne M. Itano, Till P. Rosenband, David Hume, P.O. Schmidt, Chin-Wen Chou, A. Brusch, Luca Lorini, Windell Oskay, Robert E. Drullinger, Sarah Bickman, Tara M. Fortier, Jason Stalnaker, Scott A. Diddams, William C. Swann, Nathan R. Newbury, David J. Wineland, James C. Bergquist


Frequency standards (atomic clocks) based on narrow optical transitions in 27Al+ and 199Hg+ have been developed over the past several years at NIST. These two types of standards are both based on single ions confined in Paul traps, but differ in the methods used to prepare and detect the internal atomic states. Al+ lacks a strong, laser-accessible transition for laser-cooling and for state preparation and detection. Coupling with a Be+ ion, trapped simultaneously with the Al+ ion, enables state manipulation, detection, and cooling of the Al+ ion. Both standards have achieved absolute reproducibilities of a few parts in 1017. Development of femtosecond laser frequency combs makes it possible to directly compare optical frequencies. The present determination of fAl/fHg is 1.052 871 833 148 990 438 (55), where the uncertainty is expressed in units of the least significant digit. Measurements of fAl/fHg made over about one year show a drift rate consistent with zero. This result can be used to place limits on time variations of fundamental constants such as the fine structure constant α.
Proceedings Title
Proc. 9th International Symposium on Foundations of Quantum Mechanics in the Light of New Technology
Conference Dates
August 25-28, 2008
Conference Location
Tokyo, JP


aluminum, atomic clocks, frequency standards, fundamental constants, ion traps, mercury, optical frequency standards


Itano, W. , Rosenband, T. , Hume, D. , Schmidt, P. , Chou, C. , Brusch, A. , Lorini, L. , Oskay, W. , Drullinger, R. , Bickman, S. , Fortier, T. , Stalnaker, J. , Diddams, S. , Swann, W. , Newbury, N. , Wineland, D. and Bergquist, J. (2008), Ratio of the Al<sup>+</sup> and Hg<sup>+</sup> Optical Clock Frequencies to 17 Decimal Places, Proc. 9th International Symposium on Foundations of Quantum Mechanics in the Light of New Technology, Tokyo, JP, [online], (Accessed May 23, 2024)


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Created August 25, 2008, Updated February 19, 2017