Experimental four-qubit bound entanglement

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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Figure 1: Experimental set-up for the generation of a four-qubit polarization bound-entangled state.
Figure 2: Experimental results: the density matrix.
Figure 3: Entanglement-distillation scheme.
Figure 4: Experimental set-up for Bell measurement.
Figure 5: Experimental results for the entanglement distillation.

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Acknowledgements

We acknowledge support by the Swedish Research Council (Vetenskapsrådet).

Author information

E.A. carried out the experiment. E.A. and M.B. discussed the results and wrote the manuscript. M.B. supervised the project.

Correspondence to Mohamed Bourennane.

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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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