Certification of two-qubit quantum systems with temporal inequality

TL;DR

This paper introduces a self-testing protocol for two-qubit quantum systems that certifies states and measurements through temporal inequality violations, without needing measurement compatibility or spatial separation, and is robust to noise.

Contribution

It presents a novel self-testing method based on temporal inequalities that removes the need for compatibility conditions and spatial separation in certifying two-qubit systems.

Findings

Protocol achieves maximal violation of a temporal inequality.

Method is robust to experimental errors and noise.

Certifies states and measurements without compatibility assumptions.

Abstract

Self-testing of quantum devices based on observed measurement statistics is a method to certify quantum systems using minimal resources. In Ref. [Phys. Rev. \textbf{A} 101, 032106 (2020)], a scheme based on observing measurement statistics that demonstrate Kochen-Specker contextuality has been shown to certify two-qubit entangled states and measurements without the requirement of spatial separation between the subsystems. However, this scheme assumes a set of compatibility conditions on the measurements which are crucial to demonstrating Kochen-Specker contextuality. In this work, we propose a self-testing protocol to certify the above two-qubit states and measurements without the assumption of the compatibility conditions, and at the same time without requiring the spatial separation between the subsystems. Our protocol is based on the observation of sequential correlations leading to the maximal violation of a temporal inequality derived from non-contextuality inequality. Moreover, our protocol is robust to small experimental errors or noise.