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A: Fachverband Atomphysik

A 33: Precision Spectroscopy of Atoms and Ions V (joint session A/Q)

A 33.1: Talk

Thursday, March 5, 2026, 14:30–14:45, N 3

Indium multi-ion clock operation and investigations of ground state cooling — •Shobhit Saheb Dey¹, Ingrid Maria Richter¹, Mouhamed-Omar Manai¹, Hartmut Nimrod Hausser¹, Dongliang Cong¹, Jonas Keller¹, and Tanja E. Mehlstäubler^1,2 — ¹Physikalisch-Technische Bundesanstalt, Braunschweig — ²Institut für Quantenoptik, Leibniz Universität Hannover

Optical clocks based on trapped ions are pushing forward the limits of time and frequency metrology with systematic uncertainties approaching the low 10⁻¹⁹ range, while their stability stays fundamentally limited by the Quantum Projection Noise(QPN). Uncorrelated parallel interrogation of N ions is expected to scale down the QPN limited instability by 1/√N. We establish this scaling up to 8 ions in a ¹¹⁵In⁺−¹⁷²Yb⁺ Coulomb crystal clock interrogating the ¹S₀−³P₀ clock transition of ¹¹⁵In⁺ and Doppler cooling via ¹⁷²Yb⁺ ions. Thermal motion of ions at Doppler temperature causes a time-dilation (TD) shift, which is among the largest contributors to the systematic-uncertainty budget in the ion based clocks today.

Thus, we are currently investigating ground state cooling of Coulomb crystal with tens of ions using the 360 kHz wide ¹S₀−³P₁ intercombination line in ¹¹⁵In⁺. This is expected to reduce relative shifts due to the TD to low-10⁻¹⁹ regime and we can spectroscopically measure the TD shift via interleaved clock operation.

Keywords: Optical clock, atomic physics, metrology