The mercury-ion optical clock and the search for temporal variation of fundamental constants

摘要

The repeated comparison of atomic frequency standards based upon different transitions enables the search for time variation of the fundamental constants that determine the transition frequencies. Over the course of two years we compared the frequency of the /sup 199/Hg/sup +/ 5d/sup 10/6s/sup 2/S/sub 1/2 /(F=0)/spl harr/5d/sup 9/6s/sup 2/ /sup 2/D/sub 5/2/(F=2) electric-quadrupole transition at 282 nm with the frequency of the ground-state hyperfine splitting in neutral /sup 133/Cs that defines the SI second. These measurements constrain any fractional time variation of the ratio/spl nu//sub Cs///spl nu//sub Hg/ between the two frequencies to be less than /spl plusmn/7/spl times/10/sup -15/yr/sup -1/ (1/spl sigma/ uncertainty). According to recent atomic structure calculations, this sets an upper limit to a possible fractional time variation of the product gCs(m/sub e//m/sub p/)/spl alpha//sup 6.0/ at the same level.