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.

Systematic uncertainty due to background-gas collisions in trapped-ion optical clocks



Aaron M. Hankin, Ethan Clements, Huang Yao, Samuel M. Brewer, Jwo-Sy Chen, Chin-wen Chou, David Hume, David Leibrandt


We describe a framework for calculating the frequency shift and uncertainty of trapped-ion optical atomic clocks caused by background-gas collisions, and apply this framework to an 27Al+ quantum-logic clock to enable a total fractional systematic uncertainty below 10-18. For this clock, with 38(19) nPa of room temperature H2 background gas, we find that collisional heating generates a non-thermal distribution of motional states with a mean time-dilation shift of order 10-16. However, the contribution of collisional heating to the spectroscopy signal is highly suppressed and the uncertainty of the -0.6(2.4)x10-19 calculated collision shift is dominated by the unknown collisional phase shift of the 27Al+ superposition state. We experimentally validate the framework and determine the background-gas pressure in situ using measurements of the rate of collisions that cause reordering of mixed-species ion pairs.
Physical Review Letters


atomic clocks, collisions, trapped ions


Hankin, A. , Clements, E. , Yao, H. , Brewer, S. , Chen, J. , Chou, C. , Hume, D. and Leibrandt, D. (2019), Systematic uncertainty due to background-gas collisions in trapped-ion optical clocks, Physical Review Letters, [online], (Accessed May 21, 2024)


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

Created September 30, 2019, Updated October 12, 2021