Precision Atomic Spectroscopy for Improved Limits on Variation of the Fine Structure Constant and Violation of Local Position Invariance

T. M. Fortier
N. Ashby
J. C. Bergquist
M. J. Delaney
S. A. Diddams
T. P. Heavner
L. Hollberg
W. M. Itano
Steven R. Jefferts
K. Kim


We report tests of local position invariance and the variation of fundamental constants from measurements of the frequency ratio of the 282-nm Hg+199 optical clock transition to the ground state hyperfine splitting in Cs133. Analysis of the frequency ratio of the two clocks, extending over 6 yr at NIST, is used to place a limit on its fractional variation of <5.8×10−6 per change in normalized solar gravitational potential. The same frequency ratio is also used to obtain 20-fold improvement over previous limits on the fractional variation of the fine structure constant of |α˙α|<1.3×10−16 yr−1, assuming invariance of other fundamental constants. Comparisons of our results with those previously reported for the absolute optical frequency measurements in H and Yb+171 vs other Cs133 standards yield a coupled constraint of −1.5×10−15<α˙/α<0.4×10−15 yr−1 and −2.7×10−15