Operating a multi-ion clock with dynamical decoupling

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 ⁸⁸Sr⁺ 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 7·10⁻¹⁷. 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.