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arXiv · 2404.12550

Characterizing Coherent Errors using Matrix-Element Amplification

Jonathan A. Gross·Elie Genois·Dripto M. Debroy·Yaxing Zhang·Wojciech Mruczkiewicz·Ze-Pei Cian·Zhang Jiang
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Abstract

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 $\mathrm{CZ}$ 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.

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Jonathan A. Gross, Elie Genois, Dripto M. Debroy, Yaxing Zhang, Wojciech Mruczkiewicz, Ze-Pei Cian, Zhang Jiang. 2024-04-19. Characterizing Coherent Errors using Matrix-Element Amplification. https://doi.org/10.1038/s41534-024-00917-7

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