Experimental implementation of a NMR entanglement witness |
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Authors: | J. G. Filgueiras T. O. Maciel R. E. Auccaise R. O. Vianna R. S. Sarthour I. S. Oliveira |
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Affiliation: | 1. Centro Brasileiro de Pesquisas F??sicas, Rua Dr. Xavier Sigaud 150, Rio de Janeiro, 22290-180, RJ, Brazil 2. Departamento de F??sica, ICEx, Universidade Federal de Minas Gerais, Av. Pres. Ant?nio Carlos 6627, Belo Horizonte, 31270-901, MG, Brazil 3. Empresa Brasileira de Pesquisa Agropecu??ria, Rua Jardim Botanico 1024, Rio de Janeiro, 22460-000, RJ, Brazil
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Abstract: | Entanglement witnesses (EW) allow the detection of entanglement in a quantum system, from the measurement of some few observables. They do not require the complete determination of the quantum state, which is regarded as a main advantage. On this paper it is experimentally analyzed an entanglement witness recently proposed in the context of Nuclear Magnetic Resonance experiments to test it in some Bell-diagonal states. We also propose some optimal entanglement witness for Bell-diagonal states. The efficiency of the two types of EW??s are compared to a measure of entanglement with tomographic cost, the generalized robustness of entanglement. It is used a GRAPE algorithm to produce an entangled state which is out of the detection region of the EW for Bell-diagonal states. Upon relaxation, the results show that there is a region in which both EW fails, whereas the generalized robustness still shows entanglement, but with the entanglement witness proposed here with a better performance. |
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