Abstract
Over five years, we have compared the hyperfine frequencies of and atoms in their electronic ground state using several laser-cooled and atomic fountains with an accuracy of . These measurements set a stringent upper bound to a possible fractional time variation of the ratio between the two frequencies: ( uncertainty). The same limit applies to a possible variation of the quantity , which involves the ratio of nuclear magnetic moments and the fine structure constant.
- Received 31 December 2002
DOI:https://doi.org/10.1103/PhysRevLett.90.150801
©2003 American Physical Society