Frequency Comparison of Two High-Accuracy Al+ Optical Clocks

TL;DR

This paper reports the construction and comparison of two high-accuracy Al+ optical clocks, demonstrating their stability and fractional frequency difference with unprecedented precision.

Contribution

It introduces a new Al+ optical clock with extremely low fractional frequency inaccuracy and compares it to a previous clock, advancing optical clock precision.

Findings

Fractional frequency inaccuracy of 8.6e-18

Relative stability of 2.8e-15/ sqrt(tau)

Fractional frequency difference of -1.8e-17

Abstract

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.