Reliable Characterization for Improving and Validating Accurate Quantum Operations

TL;DR

This paper introduces a reliable, self-consistent quantum operation characterization method with proven convergence and physicality, suitable for validation and improvement of quantum devices, demonstrated through 1-qubit numerical tests.

Contribution

It presents a new self-consistent estimator with regularization and physicality constraints, proven to converge reliably to the true quantum operations in validation tasks.

Findings

Estimator guarantees physical and convergent results

Method proven to converge to the true operation as data increases

Numerical tests confirm practicality for 1-qubit systems

Abstract

A reliable method for characterizing quantum operations that is suitable for improving and validating their accuracies is indispensable for realizing a practical quantum computer. Known methods are still not sufficient because they lack reliability or are not suitable for use in the improvement and validation steps. Here we propose a reliable characterization method that is suitable for the accuracy validation step. First, we introduce a new self-consistent estimator with regularization and physicality constraints that are designed for improvement and validation. Second, we mathematically prove that the method provides estimation results that are stringently physical and converge to the gauge-equivalence class of the quantum operations of interest at the limit of data size going to infinity. The asymptotic convergence guarantees the reliability of the method, and the physical and regularized results ensure the suitability to the validation task. We also derive the asymptotic convergence rate, which would be optimal. Finally, we show numerical results on 1-qubit system, which confirm the theoretical results and prove that the method proposed is practical.