Self-Testing of a Single Quantum System: Theory and Experiment

TitleSelf-Testing of a Single Quantum System: Theory and Experiment
Publication TypeJournal Article
Year of Publication2022
AuthorsHu, X-M, Xie, Y, Arora, ASingh, Ai, M-Z, Bharti, K, Zhang, J, Wu, W, Chen, P-X, Cui, J-M, Liu, B-H, Huang, Y-F, Li, C-F, Guo, G-C, Roland, J, Cabello, A, Kwek, L-C
Date Published3/17/2022
KeywordsAtomic Physics (physics.atom-ph), FOS: Physical sciences, Quantum Physics (quant-ph)

Certifying individual quantum devices with minimal assumptions is crucial for the development of quantum technologies. Here, we investigate how to leverage single-system contextuality to realize self-testing. We develop a robust self-testing protocol based on the simplest contextuality witness for the simplest contextual quantum system, the Klyachko-Can-Binicioğlu-Shumovsky (KCBS) inequality for the qutrit. We establish a lower bound on the fidelity of the state and the measurements (to an ideal configuration) as a function of the value of the witness under a pragmatic assumption on the measurements we call the KCBS orthogonality condition. We apply the method in an experiment with randomly chosen measurements on a single trapped 40Ca+ and near-perfect detection efficiency. The observed statistics allow us to self-test the system and provide the first experimental demonstration of quantum self-testing of a single system. Further, we quantify and report that deviations from our assumptions are minimal, an aspect previously overlooked by contextuality experiments.