Accurate measurements of different transition frequencies between atomic levels of the electronic and hyperfine structure over time are used to investigate temporal variations of the fine structure constant $alpha$ and the proton-to-electron mass ratio $mu$. We measure the frequency of the $^2S_{1/2}rightarrow {^2F_{7/2}}$ electric octupole (E3) transition in $^{171}$Yb$^+$ against two caesium fountain clocks as $f(E3) = 642,121,496,772,645.36(25)$~Hz with an improved fractional uncertainty of $3.9times 10^{-16}$. This transition frequency shows a strong sensitivity to changes of $alpha$. Together with a number of previous and recent measurements of the $^2S_{1/2}rightarrow {^2D_{3/2}}$ electric quadrupole transition in $^{171}$Yb$^+$ and with data from other elements, a least-squares analysis yields $(1/alpha)(dalpha/dt)=-0.20(20)times 10^{-16}/mathrm{yr}$ and $(1/mu)(dmu/dt)=-0.5(1.6)times 10^{-16}/mathrm{yr}$, confirming a previous limit on $dalpha/dt$ and providing the most stringent limit on $d mu/dt$ from laboratory experiments.
تحميل البحث