Operating a multi-ion clock with dynamical decoupling

TL;DR

This paper demonstrates a quasi-continuous dynamical decoupling scheme for multi-ion optical clocks that significantly reduces frequency shifts and inhomogeneity, enhancing stability without compromising accuracy.

Contribution

The study introduces and experimentally validates a QCDD scheme for multi-ion clocks, achieving over three orders of magnitude suppression of dominant frequency shifts.

Findings

Suppressed frequency shifts by more than three orders of magnitude.

Achieved relative frequency inhomogeneity below 7×10^{-17}.

Systematic shift from RF drive is below 10^{-17}.

Abstract

We study and characterize a quasi-continuous dynamical decoupling (QCDD) scheme that effectively suppresses dominant frequency shifts in a multi-ion optical clock. Addressing the challenge of inhomogeneous frequency shifts in such systems, our scheme mitigates primary contributors, namely the electric quadrupole shift (QPS) and the linear Zeeman shift (LZS). Based on $^{88}$Sr$^+$ ions, we implement a QCDD scheme in linear chains of up to 7 ions and demonstrate a significant suppression of the shift by more than three orders of magnitude, leading to relative frequency inhomogeneity below $7\cdot10^{-17}$. Additionally, we evaluate the associated systematic shift arising from the radiofrequency (RF) drive used in the QCDD scheme, showing that, in the presented realization, its contribution to the systematic relative frequency uncertainty is below $10^{-17}$, with potential for further improvement. These results provide a promising avenue toward implementing multi-ion clocks exhibiting an order of magnitude or more improvement in stability while maintaining a similar high degree of accuracy to that of single-ion clocks.