Improved Limits on Variation of the Fine Structure Constant and Violation of Local Position Invariance

We report tests of local position invariance (LPI) and constancy of fundamental constants from measurements of the frequency ratio of the 282-nm ¹⁹⁹Hg⁺ optical clock transition to the ground-state hyperfine splitting in ¹³³Cs. Analysis of the frequency ratio, extending over six years at NIST, is used to place a limit on the fractional variation of the two clocks of less than 5.8times10^-6 per change in normalized solar gravitational potential, and a limit on fractional variation of the fine structure constant at alpha dot/alpha < 1.3x10^-16 yr^-1, assuming invariance of other fundamental constants. Comparison of our results with those previously reported for the absolute optical frequency measurements of coupled ¹⁷¹Yb⁺ versus other constraint ¹³³Cs standard yields a coupled constraint of -0.04times10^-15 < alpha dot/alpha < 0.46times10^-15 yr^-1 and ^-2.39times10^-15 < d/dt In mu_Cs/mu_B < 0.47times10^-15 yr^-1.