Laboratory demonstration of geopotential measurement using transportable optical clocks

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 4.8×10^(−15)/√τ.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).

Observation of 1S0→3P0 Transition of a 40Ca+-27Al+ Quantum Logic Clock

We report the realization of quantum logic spectroscopy on the ^1S0→^3P0 clock transition of a single ^27Al^+ion.This ion is trapped together with a ^40Ca^+ion in a linear Paul trap,coupled by Coulomb repulsion,which provides sympathetic Doppler laser cooling and also the means for internal state detection of the clock state of the ^27Al^+ion.A repetitive quantum nondemolition measurement is performed to improve the fidelity of state detection.These techniques are applied to obtain clock spectroscopy at approximately 45 Hz.We also perform the preliminary locking on the ^1S0→^3P0 clock transition.Our work is a fundamental step that is necessary toward obtaining an ultra-precision quantum logic clock based on ^40Ca^+-^27Al^+ions.

Suppression of servo error uncertainty to 10^(-18)level using double integrator algorithm in ion optical clock

A universal locking model for single ion optical clocks was built based on a simple integrator and a double integrator.Different integrator algorithm parameters have been analyzed in both numerical simulations and experiments.The frequency variation measured by the comparison of two optical clocks coincides well with the simulation results for different second integrator parameters.According to the experimental results,the sensitivity of the servo error influenced by laser frequency drift with the addition of a double integrator was suppressed by a factor of 107.In a week-long comparison of optical clocks,the relative uncertainty of the servo error is determined to be 1.9×10^(-18),which is meaningful for the systematic uncertainty of the transportable single^(40)Ca^(+)ion optical clock entering the 10^(-18)level.