Abstract
Over 8 months, we monitored transition frequencies between nearly degenerate, opposite-parity levels in two isotopes of atomic dysprosium (Dy). These frequencies are sensitive to variation of the fine-structure constant () due to relativistic corrections of opposite sign for the opposite-parity levels. In this unique system, in contrast to atomic-clock comparisons, the difference of the electronic energies of the opposite-parity levels can be monitored directly utilizing a rf electric-dipole transition between them. Our measurements show that the frequency variation of the 3.1-MHz transition in and the 235-MHz transition in are and , respectively. These results provide a rate of fractional variation of of () without assumptions on constancy of other fundamental constants, indicating absence of significant variation at the present level of sensitivity.
- Received 1 September 2006
DOI:https://doi.org/10.1103/PhysRevLett.98.040801
©2007 American Physical Society