Experimental bilocality violation without shared reference frames

Non-classical correlations arising in complex quantum networks are attracting growing interest, both from a fundamental perspective and for potential applications in information processing. In particular, in an entanglement swapping scenario a new kind of correlations arise, the so-called nonbilocal correlations that are incompatible with local realism augmented with the assumption that the sources of states used in the experiment are independent. In practice, however, bilocality tests impose strict constraints on the experimental setup and in particular to presence of shared reference frames between the parties. Here, we experimentally address this point showing that false positive nonbilocal quantum correlations can be observed even though the sources of states are independent. To overcome this problem, we propose and demonstrate a new scheme for the violation of bilocality that does not require shared reference frames and thus constitute an important building block for future investigations of quantum correlations in complex networks.Comment: 10 page

Experimental investigation on the geometry of GHz states

Nonclassical correlations arising in complex quantum networks are attracting growing interest, both from afundamental perspective and for potential applications in information processing. In particular, in an entanglementswapping scenario a new kind of correlations arise, the so-called nonbilocal correlations that are incompatible withlocal realism augmented with the assumption that the sources of states used in the experiment are independent.In practice, however, bilocality tests impose strict constraints on the experimental setup and in particular to thepresence of shared reference frames between the parties. Here, we experimentally address this point showing thatfalse positive nonbilocal quantum correlations can be observed even though the sources of states are independent.To overcome this problem, we propose and demonstrate a scheme for the violation of bilocality that does notrequire shared reference frames and thus constitutes an important building block for future investigations ofquantum correlations in complex network

Comparación de índices de vegetación a partir de imágenes modis en la región del libertador Bernardo O´Higgins, Chile, en el período 2001-2005

Se comparan cinco índices de vegetación, NDVI, SAVI, ARVI, GreenNDVI y EVI, calculados a partir de imágenes MODIS en la Región del Libertador General Bernardo O´Higgins, Chile. Se determina las características de sus comportamientos según cubiertas vegetales distintas, zonas agrícolas, praderas y forestal, y dos periodos contrastados a lo largo del año, verano e invierno de los años 2001, 2003 y 2005. Los resultados indican que si bien las tendencias generales de las mediciones de vigor vegetal que hacen estos índices son semejantes, existen diferencias localizadas que hacen evidente la necesidad de elegir correctamente el tipo de índice de acuerdo a las necesidades que cada investigación requiera. Se hace particular énfasis en la necesidad de contar con una mayor discriminación de cubiertas vegetales para hacer una evaluación más refinada de las semejanzas y diferencias entre los índices estudiados.Five vegetation indices, NDVI, SAVI, ARVI, GreenNDVI and EVI, obtained from MODIS images in the Región del Libertador General Bernardo O´Higgins, Chile, are compared. The characteristics of their behavior according different vegetation cover layers, agricultural, grasslands and forestal zones, in both dry and wet seasons, along the years in 2001, 2003 and 2005 are determined. Results shows that global tendencies in the behavior of this indices are similar, there are some localized differences that make evident the necessity of the correct election of the right index for each situation. The importance of a more detailed discrimination in land cover types in order to achieve a better assesstment of similarities and differences between the indices is emphatized

Maximal qubit violation of n-locality inequalities in a star-shaped quantum network

Bellʼs theorem was a cornerstone for our understanding of quantum theory and the establishment ofBell non-locality played a crucial role in the development of quantum information. Recently, itsextension to complex networks has been attracting growing attention, but a deep characterization ofquantum behavior is still missing for this novel context. In this work we analyze quantum correlationsarising in the bilocality scenario, that is a tripartite quantum network where the correlations betweenthe parties are mediated by two independent sources of states. First, we prove that non-bilocalcorrelations witnessed through a Bell-state measurement in the central node of the network form asubset of those obtainable by means of a local projective measurement. This leads us to derive themaximal violation of the bilocality inequality that can be achieved by arbitrary two-qubit quantumstates and arbitrary local projective measurements. We then analyze in details the relation between theviolation of the bilocality inequality and the CHSH inequality. Finally, we show how our method canbe extended to then-locality scenario consisting ofntwo-qubit quantum states distributed amongn1+nodes of a star-shaped networ