學術演講
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2018-10-18 [Colloquium] Entanglement structure: entanglement partitioning in multipartite systems and its experimental detection using optimizable witnesses Prof. Yeong Cherng Liang(NCKU)
Abstract: 
Creating large-scale entanglement lies at the heart of many quantum information processing protocols and the investigation of fundamental physics. For multipartite quantum systems, it is crucial to identify not only the presence of entanglement but also its detailed structure. This is because, in a generic experimental situation with sufficiently many subsystems involved, the production of so-called genuine multipartite entanglement remains a formidable challenge. However, even if the system is not genuinely multipartite entangled, there may still be many-body entanglement present in the system. An identification of the entanglement structure may thus provide us with a hint on where imperfections in the setup may occur, as well as where we can identify groups of subsystems that can still exhibit strong quantum-information-processing capabilities. To date, there are no known efficient methods to identify the underlying entanglement structure. In this talk, I discuss two complementary families of witnesses for the identification of such structures. They are based, respectively, on the detection of entanglement intactness and entanglement depth, each applicable to an arbitrary number of subsystems and whose evaluation requires only the implementation of solely two local measurements. Our method is also robust against noises and other imperfections, as reflected by our experimental implementation of these tools to verify the entanglement structure of ve different eight-photon entangled states. In particular, we demonstrate how their minimal entanglement structure can be precisely and systematically inferred from the experimental measurement of these witnesses.