Sub-hertz optical frequency comparisons between two trapped 171Yb+ ions -: art. no. 230801

We compare the frequencies of the 6s S-2(1/2)(F=0)-> 5d D-2(3/2)(F=2) reference transition in Yb-171(+) for two single ions stored in independent traps. The quadrupole moment of the 5d D-2(3/2) state is measured to be 9.32(48)x10(-40) C m(2) and from the quadratic Stark shift the relevant scalar and tensor polarizabilities are determined to be alpha(S)(S-1/2)-alpha(S)(D-3/2)=-6.9(1.4)x10(-40) J m(2)/V-2 and alpha(T)(D-3/2)=-13.6(2.2)x10(-40) J m(2)/V-2, respectively. In the absence of external perturbations we find a mean frequency difference between the two trapped ions of 0.26(42) Hz, corresponding to a relative difference of 3.8(6.1)x10(-16). This is comparable to the agreement found in the most accurate comparisons between cesium fountain clocks.