Atomic optical clocks and search for variation of the fine structure constant

Abstract

Theories unifying gravity and other interactions suggest the possibility of spatial and temporal variation of physical ``constants''. Accuracy achieved for the atomic optical frequency standards (optical clocks) approaches the level when possible time evolution of the fine structure constant $α$ can be studied by comparisons of rates between clocks based on different atomic transitions in different atoms. The sensitivity to variation of $α$ is due to relativistic corrections which are different in different atoms ($\sim Z^2α^2$). We have calculated the values of the relativistic energy shifts in In II, Tl II, Ba II and Ra II which all can be used as atomic optical clocks. The results are to be used to translate any change in the clock's rate into variation of $α$.