Mainz 2026 – scientific programme
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A: Fachverband Atomphysik
A 39: Poster – Precision Measurement (joint session Q/A)
A 39.8: Poster
Thursday, March 5, 2026, 17:00–19:00, Philo 2. OG
Frequency ratio measurements at the 10−18 level with an aluminum ion clock — •Fabian Dawel1,2, Derwell Drapier1, Mirza Akbar Ali1,2, Lennart Pelzer1, Kai Dietze1,2, Bennet Benny1,2, Johannes Kramer1,2, and Piet O. Schmidt1,2 — 1PTB, Braunschweig, Germany — 2LUH, Hannover, Germany
The latest generation of optical atomic clocks claims two orders of magnitude improved statistical and systematic frequency uncertainty compared to microwave Cs-clocks. For the redefinition of the second confirmation of the estimated error budgets of optical clocks by frequency ratio measurements is required. Here, we present frequency ratio measurements of our Al+ ion clock, which is co-trapped with Ca+ for readout and cooling. The co-trapped ion allows sympathetic electromagnetically-induced transparency cooling during the clock interrogation, which reduces the second-order Doppler effect to a small and probe-time independent value. The introduced electric field of the cooling lasers can be characterized by Ca+ allowing to bound the ac-Stark shift on Al+ on a low 10−18 uncertainty level, which is the largest contribution to the total systematic frequency uncertainty of 1.7×10−18. We show frequency ratio measurements against a Sr lattice clock with a stability of 5.9×10−16√1 s/τ, limited by the Al+ ion clock stability. The resulting frequency ratio of 27Al+/87Sr shows a 14 σ difference to published results. This shows the importance of inter-institutional frequency ratio measurement for the redefinition of the second.
Keywords: Ion clock; Frequency ratio; Quantum logic spectroscopy; SI second; Ion cooling