Electric quadrupole shift cancellation in single-ion optical frequency standards -: art. no. 033001

The electric quadrupole shift is presently the most significant source of uncertainty on the systematic shifts for several single-ion optical frequency standards. We present a simple method for canceling this shift based on measurements of the Zeeman spectrum of the clock transition. This method is easy to implement and yields very high cancellation levels. A fractional uncertainty of 5x10(-18) for the canceled quadrupole shift is estimated for a measurement of the absolute frequency of the 5s S-2(1/2)-4d D-2(5/2) clock transition of Sr-88(+).