High-Accuracy Measurement Of The Differential Scalar Polarizability Of A Sr-88(+) Clock Using The Time-Dilation Effect

We report a high- accuracy measurement of the differential static scalar polarizability Delta alpha(0) of the 5s(2)S(1/2) - 4d(2)D(5/2) transition of the Sr-88(+) 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.a 0 without the need to determine the electric field..a 0 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.a 0 is - 4.7938d71 x 10- 40 Jm2= 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 x 10- 17 to 8.3 x 10- 19. The revised total uncertainty of our reference standard is 1.2 x 10- 17, limited by the blackbody field evaluation. An additional benefit of the low uncertainty of.a 0 is the ability to suppress, by a factor of about 200, the net micromotion frequency shifts.