Laboratory Limits on Temporal Variations of Fundamental Constants: An Update

Abstract

Precision comparisons of different atomic frequency standards over a period of a few years can be used for a sensitive search for temporal variations of fundamental constants. We present recent frequency measurements of the 688 THz transition in the ${}^{171}$Yb${}^{+}$ ion. For this transition frequency a record over six years is now available, showing that a possible frequency drift relative to a cesium clock can be constrained to $(-0.54\pm 0.97)$ Hz/yr, i.e. at the level of $2\cdot 10^{-15}$ per year. Combined with precision frequency measurements of an optical frequency in ${}^{199}$Hg${}^{+}$ and of the hyperfine ground state splitting in ${}^{87}$Rb a stringent limit on temporal variations of the fine structure constant $\alpha$: $d\ln \alpha /dt=(-0.26\pm 0.39)\cdot 10^{-15}{\mathrm{yr}}^{-1}$ and a model-dependent limit for variations of the proton-to-electron mass ratio $\mu$ in the present epoch can be derived: $d\ln \mu /dt=(-1.2\pm 2.2)\cdot 10^{-15}{\mathrm{yr}}^{-1}$. We discuss these results in the context of astrophysical observations that apparently indicate changes in both of these constants over the last 5--10 billion years.

10 pages, 3 figures, Proceedings of the 11th Marcel Grossmann Meeting, Berlin, 2006