The effect of noise correlations on randomized benchmarking

TL;DR

This paper develops an analytical framework to understand how temporal noise correlations affect randomized benchmarking results in quantum systems, revealing significant impacts on error distribution and interpretation.

Contribution

It introduces a comprehensive mathematical model capturing the influence of noise correlations on RB outcomes, including a gamma distribution description and insights into finite-sampling issues.

Findings

Noise correlations cause large variance and skew in RB outcomes.

RB outcome distribution can be described by a gamma distribution.

Correlated errors can lead to divergence between average and worst-case errors.

Abstract

Among the most popular and well studied quantum characterization, verification and validation techniques is randomized benchmarking (RB), an important statistical tool used to characterize the performance of physical logic operations useful in quantum information processing. In this work we provide a detailed mathematical treatment of the effect of temporal noise correlations on the outcomes of RB protocols. We provide a fully analytic framework capturing the accumulation of error in RB expressed in terms of a three-dimensional random walk in "Pauli space." Using this framework we derive the probability density function describing RB outcomes (averaged over noise) for both Markovian and correlated errors, which we show is generally described by a gamma distribution with shape and scale parameters depending on the correlation structure. Long temporal correlations impart large nonvanishing variance and skew in the distribution towards high-fidelity outcomes -- consistent with existing experimental data -- highlighting potential finite-sampling pitfalls and the divergence of the mean RB outcome from worst-case errors in the presence of noise correlations. We use the Filter-transfer function formalism to reveal the underlying reason for these differences in terms of effective coherent averaging of correlated errors in certain random sequences. We conclude by commenting on the impact of these calculations on the utility of single-metric approaches to quantum characterization, verification, and validation.