Luca Lorini, Neil Ashby, Anders Brusch, Scott A. Diddams, Robert E. Drullinger, Eric Eason, Tara M. Fortier, Pat Hastings, Thomas P. Heavner, David Hume, Wayne M. Itano, Steven R. Jefferts, Nathan R. Newbury, Thomas E. Parker, Till P. Rosenband, Jason Stalnaker, William C. Swann, David J. Wineland, James C. Bergquist
The record of atomic clock frequency comparisons at NIST over the past half-decade provides one of the tightest constraints of any present-day, temporal variations of the fundamental constants. Notably, the 6-year record of increasingly precise measurements of the absolute frequency of the Hg+ single-ion optical clock (using the cesium primary frequency standard NIST-F1) constrains the temporal variation of the fine structure constant α to less than 2 • 10-16yr-1 and offers Local Position Invariance test in the framework of General Relativity. The most recent measurement of the frequency ratio of the Al+ and Hg+ optical clocks is reported with a fractional frequency uncertainty of (5.2 • 10-17). The record of such measurements over the last year sensitively tests for a temporal variation of α and constraints (α/α = (–1.6 ± 2.3) • 10-17yr-1), consistent with zero.