Hertz-level Measurement of the 40Ca+ 4s 2S1/2-3d 2D5/2 Clock Transition Frequency With Respect to the SI Second through GPS

TL;DR

This paper reports a highly precise measurement of the 40Ca+ ion clock transition frequency, achieving an uncertainty of 1.6 Hz at around 411 THz, calibrated via GPS and a hydrogen maser, demonstrating advanced frequency metrology.

Contribution

First measurement of the 40Ca+ ion clock transition frequency with 10^-15 level uncertainty using GPS calibration.

Findings

Measured frequency: 411042129776393.0 Hz

Fractional uncertainty: 3.9×10^-15

Measurement duration: over 32 days

Abstract

We report a frequency measurement of the clock transition of a single ^40Ca^+ ion trapped and laser cooled in a miniature ring Paul trap with 10^-15 level uncertainty. In the measurement, we used an optical frequency comb referenced to a Hydrogen maser, which was calibrated to the SI second through the Global Positioning System (GPS). Two rounds of measurements were taken in May and June 2011, respectively. The frequency was measured to be 411 042 129 776 393.0(1.6) Hz with a fractional uncertainty of 3.9{\times}10^-15 in a total averaging time of > 2{\times}10^6 s within 32 days.