Frequency Comparison of Al+ and Hg+ Optical Standards
Till P. Rosenband, David Hume, Anders Brusch, Luca Lorini, P. O. Schmidt, Tara M. Fortier, Jason Stalnaker, Scott A. Diddams, Nathan R. Newbury, W Swann, Windell Oskay, Wayne M. Itano, David J. Wineland, James C. Bergquist
We compare the frequencies of two single ion frequency standards: 27Al+ and 199Hg+. Systematic fractional frequency uncertainties of both standards are below 10-16, and the statistical measurement uncertainty is below 5 x 10-17. Recent ratio measurements show a reproducibility that is better than 10-16.