[time-nuts] A beautiful triptych of recent optical clock papers from NIST and JILA

[Serge Belyshev]

... that I came across recently and would like to share:

1. "Towards the optical second: verifying optical clocks at the SI limit"
by W. F. McGrew et al: https://doi.org/10.1364/OPTICA.6.000448 (open access)
-- reports best absolute measurement of Yb-171 optical transition in a
lattice clock with fractional uncertainity of 2×10^-16. (See also their
supplementary material with absolute frequency comparisons of other best
performing clocks).

2. "Optical clock intercomparison with 6×10^−19 precision in one hour"
by E. Oelker et al.: https://arxiv.org/abs/1902.02741
-- sets frequency stability record of 4×10^-17/sqrt(tau) in Sr-87 lattice clock.
Performance of their flywheel oscillator -- cryogenic silicon reference cavity
1542nm laser is truly awesome.

3. "An 27Al+ quantum-logic clock with systematic uncertainty below 10^-18"
by S. M. Brewer et al.:  https://arxiv.org/abs/1902.07694
-- compared to lattice clocks with thousands of atoms, a lone trapped Al-27+ ion
quantum logic clock is limited by quantum projection noise 'only' to
10^-15/sqrt(tau), but instead achieves best systematic uncertainity below
10^-18 level.