ATOMIC CLOCKS AND VARIATIONS OF THE FINE-STRUCTURE CONSTANT

We describe a new test for possible variations of the fine structure constant by comparisons of rates between clocks based on hyperfine transitions in alkali atoms with different atomic number Z. H-maser, Cs, and Hg + clocks have a different dependence on via relativistic contributions of order (Z)2. Recent H-maser vs Hg+ clock comparison data improve laboratory limits on a time variation by 100-fold to give /3.7×10-14/yr. Future laser cooled clocks (Be +, Rb, Cs, Hg +, etc.), when compared, will yield the most sensitive of all tests for /. © 1995 The American Physical Society.