Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Frequency Comparison of Two High-Accuracy Al+ Optical Clocks



Chin-Wen Chou, David Hume, J.C. Koelemeij, David J. Wineland, Till P. Rosenband


We have constructed an optical clock with a fractional frequency inaccuracy of 8.6e-18, based on quantum logic spectroscopy of an Al+ ion. A simultaneously trapped Mg+ ion serves to sympathetically laser-cool the Al+ ion and detect its quantum state. The frequency of the 1S0->3P0 clock transition is compared to that of a previously constructed Al+ optical clock with a statistical measurement uncertainty of 7.0e-18. The two clocks exhibit a relative stability of 2.8e-15/ sqrt(tau), and a fractional frequency difference of -1.8e-17, consistent with the accuracy limit of the older clock.
Physical Review Letters


atomic clock, optical clock, high accuracy, aluminum ion, quantum logic


Chou, C. , Hume, D. , Koelemeij, J. , Wineland, D. and Rosenband, T. (2010), Frequency Comparison of Two High-Accuracy Al+ Optical Clocks, Physical Review Letters, [online], (Accessed May 28, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created February 17, 2010, Updated February 19, 2017