Accuracy, Stability, and Comparisons with the JILA Strontium 1D Optical Lattice Clock

Clocks based upon optical transitions have far surpassed microwave atomic clocks in both accuracy and stability. Our system is based upon the narrow clock transition in a sample of fermionic strontium atoms confined in a 1D optical lattice. With precise environmental and sample control, we have recently demonstrated record low systematic uncertainty of 8e-19 [1] as well as quantum projection noise limited performance below 4e-18 at 1 second [2]. To ensure accuracy at this level and benchmark the reliability of optical clocks in general, it is necessary to perform frequency comparisons with other high accuracy systems [3]. We are currently performing frequency comparisons with the aluminum ion and neutral ytterbium clocks at NIST, making use of our ultra-stable cryogenic silicon cavity as a shared oscillator distributed over a phase-stabilized optical network. This allows us to perform intraspecies remote comparisons with very low instability, enabling fast averaging to the combined accuracy budget. Such frequency ratio measurements are important for redefinition of the SI second and support searches for ultralight dark matter.

[1] Aeppli et al., Phys. Rev. Lett. 133, 023401, 2024.

[2] Bothwell et al., Nature 602, 2022.

[3] BACON Collaboration, Nature 591, 2021.