Abstract
The - clock transition frequency in neutral has been measured relative to the Cs standard by three independent laboratories in Boulder, Paris, and Tokyo over the last three years. The agreement on the level makes the best agreed-upon optical atomic frequency. We combine periodic variations in the clock frequency with and H-maser data to test local position invariance by obtaining the strongest limits to date on gravitational-coupling coefficients for the fine-structure constant , electron-proton mass ratio , and light quark mass. Furthermore, after , , and H, we add as the fourth optical atomic clock species to enhance constraints on yearly drifts of and .
- Received 11 January 2008
DOI:https://doi.org/10.1103/PhysRevLett.100.140801
©2008 American Physical Society