Easier randomizing gates provide more accurate fidelity estimation

TL;DR

This paper compares different randomized benchmarking methods for quantum gates, showing that simpler cycle benchmarking with single-qubit Pauli gates yields more accurate error estimates than standard multi-qubit Clifford-based methods, especially with coherent errors.

Contribution

It demonstrates that cycle benchmarking reduces systematic errors and improves fidelity estimation accuracy over traditional interleaved randomized benchmarking methods.

Findings

Cycle benchmarking provides more accurate error estimates.

Standard IRB can give highly inaccurate or impossible estimates.

Experimental results confirm theoretical predictions.

Abstract

Accurate benchmarking of quantum gates is crucial for understanding and enhancing the performance of quantum hardware. A standard method for this is interleaved benchmarking, a technique which estimates the error on an interleaved target gate by comparing cumulative error rates of randomized sequences implemented with the interleaved gate and without it. In this work, we show both numerically and experimentally that the standard approach of interleaved randomized benchmarking (IRB), which uses the multi-qubit Clifford group for randomization, can produce highly inaccurate and even physically impossible estimates for the error on the interleaved gate in the presence of coherent errors. Fortunately we also show that interleaved benchmarking performed with cycle benchmarking, which randomizes with single qubit Pauli gates, provides dramatically reduced systematic uncertainty relative to standard IRB, and further provides as host of additional benefits including data reusability. We support our conclusions with a theoretical framework for bounding systematic errors, extensive numerical results comparing a range of interleaved protocols under fixed resource costs, and experimental demonstrations on three quantum computing platforms.