High-Accuracy Measurement of the Differential Scalar Polarizability of a 88Sr+ Clock Using the Time-Dilation Effect.

We report a high-accuracy measurement of the differential static scalar polarizability Δα0 of the 5s2S1/2-4d2D5/2 transition of the 88Sr+ ion. The high accuracy is obtained by comparing the micromotion-induced positive scalar Stark shift to the negative time-dilation shift. Measurement of the trap drive frequency where these shifts cancel is used to determine Δα0 without the need to determine the electric field. Δα0 is a critical parameter for the operation of frequency standards as it determines the blackbody radiation frequency shift coefficient, the largest source of uncertainty in the 88Sr+ ion clock. The measured value of Δα0 is -4.7938(71) × 10-40 J m2/V2. Taking into account the dynamic correction, the blackbody shift at 300 K is 0.247 99(37) Hz. The contribution of the blackbody shift coefficient to the uncertainty of the ion standard has been reduced by a factor of 24, from 2 × 10-17 to 8.3 ×10-19. The revised total uncertainty of our reference standard is 1.2 × 10-17, limited by the blackbody field evaluation. An additional benefit of the low uncertainty of Δα0 is the ability to suppress, by a factor of about 200, the net micromotion frequency shifts. [ABSTRACT FROM AUTHOR]