Loop State-preparation-and-measurement tomography of a two-qubit system

TL;DR

This paper demonstrates that loop state-preparation-and-measurement (SPAM) tomography can detect correlated errors in a two-qubit system without assumptions about state or measurement specifics, enhancing quantum processor reliability.

Contribution

The paper introduces an experimental application of loop SPAM tomography to identify correlated errors in a two-qubit system, showing its effectiveness without relying on detailed prior knowledge.

Findings

Successfully detected correlated errors in a two-qubit system.

Validated loop SPAM tomography as a practical tool for quantum error detection.

Demonstrated robustness in identifying errors without assumptions on state or measurement details.

Abstract

We experimentally demonstrate that loop state-preparation-and-measurement (SPAM) tomography is capable of detecting correlated errors in a two-qubit system. We prepare photon pairs in a state that approximates a Werner state, which may or may not be entangled. By performing measurements with multiple different detector settings we are able to detect correlated errors between two single-qubit measurements performed in different locations. No assumptions are made concerning either the state preparations or the measurements, other than that the dimensions of the states and the positive-operator-valued measures describing the detectors are known. The only other needed information is experimentally measured expectation values, which are analyzed for self-consistency. This demonstrates that loop SPAM tomography is a useful technique for detecting errors that would degrade the performance of multiple-qubit quantum information processors.