Laboratory demonstration of geopotential measurement using transportable optical clocks
Daoxin Liu, Jian Cao, Jinbo Yuan, Kaifeng Cui, Yi Yuan, Ping Zhang, Sijia Chao, Hua-Lin Shu, Xue-Ren Huang
Abstract
We report an experimental demonstration of geopotential difference measurement using a pair of transportable 40 Ca + optical clocks (TOC-729-1 and TOC-729-3) in the laboratory, each of them has an uncertainty of 1.3 × 10 −17 and an instability of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>4.8</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>15</mml:mn> </mml:mrow> </mml:msup> <mml:mo>/</mml:mo> <mml:msqrt> <mml:mi>τ</mml:mi> </mml:msqrt> </mml:mrow> </mml:math> . 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) × 10 −17 , considering both the statistic (1.0 × 10 −17 ) and the systematic (1.9 × 10 −17 ) uncertainties. The frequency difference between these two clocks is within their respective uncertainties, verifying the reliability of transportable 40 Ca + optical clocks at the low level of 10 −17 .