Characterization of coherent errors in gate layers with robustness to Pauli noise

TL;DR

This paper introduces a practical protocol for characterizing coherent errors in quantum gate layers that remains robust in the presence of Pauli noise, aiding in device calibration and error mitigation.

Contribution

It extends incoherent noise models to include coherent errors and provides a robust, practical characterization method applicable to arbitrary gate layers.

Findings

Successfully demonstrated on superconducting hardware

Identified leading coherent errors in the device

Improved error mitigation by characterizing noise structure

Abstract

Characterization of quantum devices generates insights into their sources of disturbances. State-of-the-art characterization protocols often focus on incoherent noise and eliminate coherent errors when using Pauli or Clifford twirling techniques. This approach biases the structure of the effective noise and adds a circuit and sampling overhead. We motivate the extension of an incoherent local Pauli noise model to coherent errors and present a practical characterization protocol for an arbitrary gate layer. Notably, the coherent noise estimation is robust to Pauli noise. We demonstrate our protocol on a superconducting hardware platform and identify the leading coherent errors. To verify the characterized noise structure, we mitigate its coherent and incoherent components using a gate-level coherent noise mitigation scheme in conjunction with probabilistic error cancellation. The proposed characterization procedure opens up possibilities for device calibration, hardware development, and improvement of error mitigation and correction techniques.