Abstract
Entanglement is one of the most puzzling features of quantum theory and of great importance for the new field of quantum information. Being a peculiar form of entanglement, bound entanglement emerges in certain mixed quantum states. This form of entanglement is not distillable by local operators and classical communication. Bound-entangled states are different from both the free entangled (distillable) and separable states. Here we report on the first experimental demonstration of a four-qubit polarization bound-entangled state, the so-called Smolin state. We have fully characterized its entanglement properties. Moreover, we have realized unlocking of the entanglement protocol for this state. The special properties of the Smolin state constitute a useful quantum resource for new multiparty communication schemes.
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Acknowledgements
We acknowledge support by the Swedish Research Council (VetenskapsrĂ¥det).
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E.A. carried out the experiment. E.A. and M.B. discussed the results and wrote the manuscript. M.B. supervised the project.
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Amselem, E., Bourennane, M. Experimental four-qubit bound entanglement. Nature Phys 5, 748–752 (2009). https://doi.org/10.1038/nphys1372
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DOI: https://doi.org/10.1038/nphys1372
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