The very best atomic clocks today are known as optical clocks, because their timebase resides at a very high frequency (~1015 Hz), corresponding to the optical domain of the electromagnetic spectrum.
In recent years, optical clocks have achieved performance that is orders of magnitude beyond more traditional atomic clocks utilizing a microwave timebase. A particularly promising type of advanced optical clock is the optical lattice clock. At their heart, these systems use an ensemble of ultracold, laser-cooled atoms confined in a periodic laser trap known as an optical lattice. A number of atomic species are well-suited for use in optical lattice clocks, and we are developing them with 171Yb (ytterbium). NIST Yb lattice clocks push the frontiers of atomic timekeeping, and have set world records in the most critical figure-of-merits for optical clocks including frequency stability, systematic uncertainty, and reproducibility. For example, comparisons between two Yb lattice clocks have demonstrated consistency with a total fractional frequency uncertainty of 1x10-18. These clocks are also frequently measured with and compared to other optical and microwave clocks at NIST and beyond. These cross-species comparisons play a critical role in efforts to update and re-define our standard unit of time, the SI second. We also leverage the extreme precision that these type of measurements realize in order to test fundamental laws of physics, including searches for physics beyond the Standard Model. In the quest to make these clocks even more precise, we actively research new quantum control and measurement techniques, new laser-cooling strategies, extreme laser stabilization, ultra-coherent light-atom interactions, and enhanced control of systematic effects that impact the fundamental limits of optical clocks.
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