Laboratory demonstration of geopotential measurement using transportable optical clocks

We report an experimental demonstration of geopotential difference measurement using a pair of transportable 40Ca+ optical clocks (TOC-729-1 and TOC-729-3) in the laboratory, each of them has an uncertainty of 1.3 x 10(-17) and an instability of 4.8 x 10(-15)/root tau. Referenced to a stationary clock of TOC-729-1, the geopotential difference measurements are realized by moving TOC-729-3 to three different locations and the relevant altitude differences are measured with uncertainties at the level of 20 cm. After correcting the systematic shifts (including gravitational red shift), the two-clock frequency difference is measured to be -0.7(2.2) x 10(-17), considering both the statistic (1.0 x 10(-17)) and the systematic (1.9 x 10(-17)) uncertainties. The frequency difference between these two clocks is within their respective uncertainties, verifying the reliability of transportable 40Ca+ optical clocks at the low level of 10(-17).

Automated summary

In this study, an experimental demonstration of geopotential difference measurement was carried out using a pair of transportable 40Ca+ optical clocks (TOC-729-1 and TOC-729-3) in the laboratory. The uncertainty of each clock is 1.3 x 10(-17) and the instability is 4.8 x 10(-15)/root tau. By moving TOC-729-3 to three different locations and measuring the relevant altitude differences, the measurements achieved an accuracy level of 20 cm. After correcting for systematic shifts, the frequency difference between the two clocks was measured to be -0.7(2.2) x 10(-17), considering both statistical (1.0 x 10(-17)) and systematic (1.9 x 10(-17)) uncertainties. The frequency difference between these two clocks is within their respective uncertainties, confirming the reliability of transportable 40Ca+ optical clocks at the low level of 10(-17).