A strontium optical lattice clock with 8×10^-19 systematic uncertainty

Optical atomic clocks have revolutionized timekeeping, leading to the most accurate and precise measurements ever made. Achieving this level of performance requires precise quantum control of the atoms and comprehensive characterization and stabilization of systematic frequency shifts. Using a laser based upon a single-crystal silicon resonator, we probe the ultra-narrow 5s^2 1S₀ → 5s5p ³P₀ electronic transition in strontium atoms confined in a one-dimensional optical lattice. In-situ imaging allows us to rapidly measure frequency gradients within an atomic sample, including the gravitational redshift over less than a millimeter. Tuning the trap to a "magic depth,'" we modify the external atomic wavefunction to cancel the density shift. Remeasuring the atomic response function and carefully determining the radiant temperature reduce the blackbody radiation shift. After characterizing the light shift, the remaining systematic effects are constrained to significantly smaller uncertainties for a total fractional uncertainty of 8.1×10^-19. This platform has enabled frequency comparisons with optical clocks at NIST yielding some of the most accurate frequency ratios measured. Finally, we extend clock performance by mapping out the coherence limitations of both the laser and strontium systems.

*Work done under the supervision of Jun Ye at JILA/University of Colorado, Boulder, CO, USA