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 noise, while its efficiency is 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. We use MEADD to estimate coherent parameters of CZ gates with 5 to 10 times the precision of existing methods and to characterize previously undetectable coherent crosstalk, reaching a precision below one milliradian.

多次重复一个门序列会相干地放大系统误差，使其成为表征量子门的有用工具。然而，这种方法的精度受到低频噪声的限制，而其效率则受到匹配被放大的非对角矩阵元素相位所需的耗时扫描的阻碍。在这里，我们通过在称为使用动态解耦的矩阵元件扩增 （MEADD） 的方案中将目标门与动态解耦序列交错来克服这两个挑战。使用来自 Google Sycamore 量子处理器的可调谐频率超导量子比特，我们实验证明 MEADD 在估计单量子比特和双量子比特门中的系统误差方面超越了现有表征协议的准确性和精密度。我们使用 MEADD 以现有方法的 5 到 10 倍的精度估计 CZ 门的相干参数，并表征以前无法检测到的相干串扰，精度达到 1 毫弧度以下。