Self-testing of a single quantum system from theory to experiment

• Published in: npj quantum information Vol. 9; no. 1; pp. 103 - 11
• Main Authors: Hu, Xiao-Min, Xie, Yi, Arora, Atul Singh, Ai, Ming-Zhong, Bharti, Kishor, Zhang, Jie, Wu, Wei, Chen, Ping-Xing, Cui, Jin-Ming, Liu, Bi-Heng, Huang, Yun-Feng, Li, Chuan-Feng, Guo, Guang-Can, Roland, Jérémie, Cabello, Adán, Kwek, Leong-Chuan
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 19.10.2023; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/259; 639/766/483/481; Classical and Quantum Gravitation; Communication; Experiments; Laboratories; Physics; Physics and Astronomy; Quantum Computing; Quantum Field Theories; Quantum Information Technology; Quantum Physics; Relativity Theory; Science; Spintronics; String Theory; Tomography
• ISSN: 2056-6387; 2056-6387
• DOI: 10.1038/s41534-023-00769-7

Self-testing allows one to characterise quantum systems under minimal assumptions. However, existing schemes rely on quantum nonlocality and cannot be applied to systems that are not entangled. Here, we introduce a robust method that achieves self-testing of individual systems by taking advantage of contextuality. The scheme is based on the simplest contextuality witness for the simplest contextual quantum system—the Klyachko-Can-Binicioğlu-Shumovsky inequality for the qutrit. We establish a lower bound on the fidelity of the state and the measurements as a function of the value of the witness under a pragmatic assumption on the measurements. We apply the method in an experiment on a single trapped 40 Ca + using randomly chosen measurements and perfect detection efficiency. Using the observed statistics, we obtain an experimental demonstration of self-testing of a single quantum system.