Measurement of the static scalar polarizability of the 88Sr+ clock transition

We have reported recently a high-accuracy measurement of the differential static scalar polarizability, Δα₀, of the clock transition of ⁸⁸Sr⁺. In this paper, we review the method used to make this measurement and the results obtained. Δα₀ is an essential parameter for the control of the systematic shifts in ion optical frequency standards as it determines the blackbody radiation shift coefficient and the scalar Stark shift caused by micromotion. The new experimental value of Δα₀ reduces the uncertainty of the blackbody radiation shift coefficient by a factor of 24, from 2 × 10^-17 to 8.3 × 10^-19. In addition, Δα₀ determines the trap rf frequency for optimum cancellation of the positive Stark shift with the negative time-dilation shift. A suppression factor of more than 200 is obtained with the new value of Δα₀, resulting in a net micromotion shift fractional uncertainty at the 10^-19 level.