Limit on the Temporal Variation of the Fine-Structure Constant Using Atomic Dysprosium

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 ($\ensuremath{\alpha}$) 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 $^{163}\mathrm{Dy}$ and the 235-MHz transition in $^{162}\mathrm{Dy}$ are $9.0\ifmmode\pm\else\textpm\fi{}6.7\text{ }\text{ }\mathrm{Hz}/\mathrm{yr}$ and $\ensuremath{-}0.6\ifmmode\pm\else\textpm\fi{}6.5\text{ }\text{ }\mathrm{Hz}/\mathrm{yr}$, respectively. These results provide a rate of fractional variation of $\ensuremath{\alpha}$ of $(\ensuremath{-}2.7\ifmmode\pm\else\textpm\fi{}2.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}\text{ }{\mathrm{yr}}^{\ensuremath{-}1}$ ($1\ensuremath{\sigma}$) without assumptions on constancy of other fundamental constants, indicating absence of significant variation at the present level of sensitivity.