Measurement of the 199Hg+ 5d96s2 2D5/2 electric quadrupole moment and a constraint on the quadrupole shift -: art. no. 163001

The electric-quadrupole moment of the Hg-199(+) 5d(9)6s(2) D-2(5/2) state is measured to be Theta(D,5/2)=-2.29(8)x10(-40) C m(2). This value was determined by measuring the frequency of the Hg-199(+) 5d(10)6s S-2(1/2)-> 5d(9)6s(2) D-2(5/2) optical clock transition for different applied electric-field gradients. An isolated, mechanically stable optical cavity provides a frequency reference for the measurement. We compare the results with theoretical calculations and discuss the implications for the accuracy of an atomic clock based upon this transition. We now expect that the frequency shift caused by the interaction of the quadrupole moment with stray electric-field gradients will not limit the accuracy of the Hg+ optical clock at the 10(-18) level.