Print Email Facebook Twitter Robust self-testing of two-qubit states Title Robust self-testing of two-qubit states Author Coopmans, T.J. (TU Delft QID/Elkouss Group; TU Delft QuTech Advanced Research Centre) Kaniewski, Jȩdrzej (Polish Academy of Sciences) Schaffner, Christian (Universiteit van Amsterdam) Date 2019 Abstract It is well known that observing nonlocal correlations allows us to draw conclusions about the quantum systems under consideration. In some cases this yields a characterisation which is essentially complete, a phenomenon known as self-testing. Self-testing becomes particularly interesting if we can make the statement robust, so that it can be applied to a real experimental setup. For the simplest self-testing scenarios the most robust bounds come from the method based on operator inequalities. In this work we elaborate on this idea and apply it to the family of tilted Clauser-Horne-Shimony-Holt (CHSH) inequalities. These inequalities are maximally violated by partially entangled two-qubit states and our goal is to estimate the quality of the state based only on the observed violation. For these inequalities we have reached a candidate bound and while we have not been able to prove it analytically, we have gathered convincing numerical evidence that it holds. Our final contribution is a proof that in the usual formulation, the CHSH inequality only becomes a self-test when the violation exceeds a certain threshold. This shows that self-testing scenarios fall into two distinct classes depending on whether they exhibit such a threshold or not. To reference this document use: http://resolver.tudelft.nl/uuid:43f62c6c-d96e-472f-83e9-67ef2c2482d8 DOI https://doi.org/10.1103/PhysRevA.99.052123 ISSN 2469-9926 Source Physical Review A: covering atomic, molecular, and optical physics and quantum information, 99 (5) Part of collection Institutional Repository Document type journal article Rights © 2019 T.J. Coopmans, Jȩdrzej Kaniewski, Christian Schaffner Files PDF PhysRevA.99.052123.pdf 527.82 KB Close viewer /islandora/object/uuid:43f62c6c-d96e-472f-83e9-67ef2c2482d8/datastream/OBJ/view