Al+ optical clocks for fundamental physics, geodesy, and quantum metrology

We compare the rates of two Al+ optical clocks. Despite many differences, their rates agree to 1.8 +/− 0.7 × 10−17, within the accuracy limit of the older clock. The newer clock has an accuracy of 8.6 × 10−18 and stability near 10−15 (τ/s)−1/2.