Repeating a gate sequence multiple times amplifies systematic errors coherently, making it a useful tool for characterizing quantum gates. However, the precision of such an approach is limited by low-frequency noises, while its efficiency hindered by time-consuming scans required to match up the phases of the off-diagonal matrix elements being amplified. Here, we overcome both challenges by interleaving the gate of interest with dynamical decoupling sequences in a protocol we call Matrix-Element Amplification using Dynamical Decoupling (MEADD). Using frequency-tunable superconducting qubits from a Google Sycamore quantum processor, we experimentally demonstrate that MEADD surpasses the accuracy and precision of existing characterization protocols for estimating systematic errors in single- and two-qubit gates. In particular, MEADD yields factors of 5 to 10 improvements in estimating coherent parameters of the CZ gates compared to existing methods, reaching a precision below one milliradian. We also use it to characterize coherent crosstalk in the processor which was previously too small to detect reliably.
@article{arxiv.2404.12550,
title = {Characterizing Coherent Errors using Matrix-Element Amplification},
author = {Jonathan A. Gross and Elie Genois and Dripto M. Debroy and Yaxing Zhang and Wojciech Mruczkiewicz and Ze-Pei Cian and Zhang Jiang},
journal= {arXiv preprint arXiv:2404.12550},
year = {2025}
}