Single trusted qubit is necessary and sufficient for quantum realization of extremal no-signaling correlations

• Published in: npj quantum information Vol. 8; no. 1; pp. 1 - 6
• Main Authors: Ramanathan, Ravishankar, Banacki, Michał, Ravell Rodríguez, Ricard, Horodecki, Paweł
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 04.10.2022; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/259; 639/766/483/2802; 639/766/483/481; Behavior; Boxes; Classical and Quantum Gravitation; Cryptography; Physics; Physics and Astronomy; Quantum Computing; Quantum Field Theories; Quantum Information Technology; Quantum Physics; Quantum theory; Relativity Theory; Spintronics; String Theory
• ISSN: 2056-6387; 2056-6387
• DOI: 10.1038/s41534-022-00633-0

The problem of achieving security of device-independent (or semi-device-independent) cryptography (for quantum key distribution and randomness generation) against the most general no-signaling adversaries has remained open. It has been recognized that the realization of extremal no-signaling non-local boxes (or extremal no-signaling non-local assemblages) could provide a route toward devising such highly secure protocols. We first prove a general no-go result that in the Bell non-locality scenario, quantum theory does not allow us to realize any extremal no-signaling non-local box, even if scenarios of arbitrary sequential measurements are considered. On the other hand, we secondly prove a positive result showing that a one-sided device-independent scenario where a single party trusts their qubit system is already sufficient for quantum theory to realize a self-testing extremal non-local point within the set of no-signaling assemblages.