Self-testing, aka device-independent tomography, refers to the fact that some quantum states and measurements can be uniquely determined from the observed statistics, without any prior characterisation of the properties that are being measured. In this recent work, we combine self-testing with the possibility of inferring global information from marginal information, which is often the only information one can gather in many body systems. We exhibit the first examples of self-testing of multipartite quantum states by marginal information: the self-testing of the three-qubit W state, as well as a family of related states, by two-body correlations; and the self-testing of the state that maximizes a Bell function involving only two-body correlations. Based on arXiv:1808.02223.
Cai Yu obtained his PhD from the Centre for Quantum Technologies, Singapore, under the supervision of Valerio Scarani. He is now a research fellow at CQT. His main research interests are Bell nonlocality, device-independent certifications and quantum foundation.