Sr lattice clock at 1x10^{-16} fractional uncertainty by remote optical evaluation with a Ca clock

Understand

Optical atomic clocks promise timekeeping at the highest precision and accuracy, owing to their high operating frequencies.

• Rigorous evaluations of these clocks require direct comparisons between them.
• We have realized a high-performance remote comparison of optical clocks over km-scale urban distances, a key step for development, dissemination, and application of these optical standards.
• Through this remote comparison and a proper design of lattice-confined neutral atoms for clock operation, we evaluate the uncertainty of a strontium (Sr) optical lattice clock at the 1x10-16 fractional level, surpassing the best current evaluations of cesium (Cs) primary standards.