Testing the stability of fundamental constants with the 199Hg+ single-ion optical clock -: art. no. 150802

Over a two-year duration, we have compared the frequency of the Hg-199 + 5d(10)6s S-2(1/2) (F = 0) <-> 5d(9)6s(2) D-2(5/2) (F = 2) electric-quadrupole transition at 282 nm with the frequency of the ground-state hyperfine splitting in neutral Cs-133. These measurements show that any fractional time variation of the ratio nu(Cs)/nu(Hg) between the two frequencies is smaller than +/-7 x 10(-15) yr(-1) (1sigma uncertainty). According to recent atomic structure calculations, this sets an upper limit to a possible fractional time variation of g(Cs)(m(e)/m(p))alpha(6.0) at the same level.