Detecting crosstalk errors in quantum information processors

TL;DR

This paper introduces a comprehensive framework and an efficient protocol for detecting and localizing crosstalk errors in multi-qubit quantum processors, crucial for improving fault-tolerance in quantum computing.

Contribution

It provides a rigorous and operational definition of crosstalk errors, along with a scalable detection protocol applicable to multi-qubit systems.

Findings

Protocol successfully detects crosstalk errors in simulations

Detection efficiency scales quadratically or cubically with qubit number

Framework captures a wide range of physical crosstalk phenomena

Abstract

Crosstalk occurs in most quantum computing systems with more than one qubit. It can cause a variety of correlated and nonlocal crosstalk errors that can be especially harmful to fault-tolerant quantum error correction, which generally relies on errors being local and relatively predictable. Mitigating crosstalk errors requires understanding, modeling, and detecting them. In this paper, we introduce a comprehensive framework for crosstalk errors and a protocol for detecting and localizing them. We give a rigorous definition of crosstalk errors that captures a wide range of disparate physical phenomena that have been called "crosstalk", and a concrete model for crosstalk-free quantum processors. Errors that violate this model are crosstalk errors. Next, we give an equivalent but purely operational (model-independent) definition of crosstalk errors. Using this definition, we construct a protocol for detecting a large class of crosstalk errors in a multi-qubit processor by finding conditional dependencies between observed experimental probabilities. It is highly efficient, in the sense that the number of unique experiments required scales at most cubically, and very often quadratically, with the number of qubits. We demonstrate the protocol using simulations of 2-qubit and 6-qubit processors.