Data: Sexta-Feira 22/08/2014, Sala A5-01, 11 am

Palestrante: Marcos Cesar de Oliveira (UNICAMP)

Título: Non-Classicality and Complementarity in two-level systems

Resumo: The principle of complementarity, introduced by Bohr, relies on the observation that in quantum systems, certainty in the measurement of a fixed physical property precludes certainty in the measurement of a complementary one. The paradigma is the double slit experiment, where complementarity is embodied by the which path information and the observation of interference fringes. In fact it is possible to construct a quasiprobability representation in terms of mutually unbiased bases (MUB) that capture the notion of complementarity in the measurements of a system. States in the convex hull of the MUB set have a positive representation, while those outside necessarily display some negativity and are thus nonclassical in this representation. However, the quasiprobability does not rule out superquantum states. In this talk we discuss those aspects of nonclassicality and complementarity for two-level systems. Particularly, we consider the consequences of hypothetical violations of the principle of complementarity and show that any preparation violating complementarity enables the preparation of a nonsignalling box violating Tsirelson’s bound. Moreover, these superquantum objects could be used to distinguish a plethora of non-orthogonal quantum states and hence enable improved cloning protocols.

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