Robust, self-consistent, closed-form tomography of quantum logic gates on a trapped ion qubit

TL;DR

This paper introduces a comprehensive framework called gate set tomography (GST) for self-consistently characterizing quantum logic gates, including a closed-form linear-inversion protocol and an objective accuracy scoring method, demonstrated on trapped-ion qubits.

Contribution

The paper presents a new self-consistent GST framework, an explicit closed-form LGST protocol, and an objective scoring method for quantum gate characterization, with experimental validation on trapped-ion qubits.

Findings

GST accurately characterizes quantum gates without reference to target gates.

LGST protocol is reliable and independent of likelihood pathologies.

Comparison shows GST outperforms standard process tomography.

Abstract

We introduce and demonstrate experimentally: (1) a framework called "gate set tomography" (GST) for self-consistently characterizing an entire set of quantum logic gates on a black-box quantum device; (2) an explicit closed-form protocol for linear-inversion gate set tomography (LGST), whose reliability is independent of pathologies such as local maxima of the likelihood; and (3) a simple protocol for objectively scoring the accuracy of a tomographic estimate without reference to target gates, based on how well it predicts a set of testing experiments. We use gate set tomography to characterize a set of Clifford-generating gates on a single trapped-ion qubit, and compare the performance of (i) standard process tomography; (ii) linear gate set tomography; and (iii) maximum likelihood gate set tomography.