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Experimental entanglement distillation and ‘hidden’ non-locality

Nature volume 409, pages 1014–1017 (2001)Cite this article

Abstract

Entangled states are central to quantum information processing, including quantum teleportation1, efficient quantum computation2 and quantum cryptography3. In general, these applications work best with pure, maximally entangled quantum states. However, owing to dissipation and decoherence, practically available states are likely to be non-maximally entangled, partially mixed (that is, not pure), or both. To counter this problem, various schemes of entanglement distillation, state purification and concentration have been proposed4,5,6,7,8,9,10,11. Here we demonstrate experimentally the distillation of maximally entangled states from non-maximally entangled inputs. Using partial polarizers, we perform a filtering process to maximize the entanglement of pure polarization-entangled photon pairs generated by spontaneous parametric down-conversion12,13. We have also applied our methods to initial states that are partially mixed. After filtering, the distilled states demonstrate certain non-local correlations, as evidenced by their violation of a form of Bell's inequality14,15. Because the initial states do not have this property, they can be said to possess ‘hidden’ non-locality6,16.

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Figure 1: Experimental set-up used to investigate entanglement distillation and hidden non-locality.
Figure 2: Experimental results showing entanglement distillation of non-maximally entangled states.
Figure 3: Contour plots in the ε–λ plane, showing the curves for S = 2, for states of the form (2).
Figure 4: Density matrices for states displaying ‘hidden’ non-locality.

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Acknowledgements

We thank H. Bernstein, D. DiVincenzo, B.-G. Englert, L. Hardy, D. James and M. Zukowski for helpful discussions. This work was supported in part by the National Security Agency (NSA) and Advanced Research and Development Activity (ARDA), and by the European IST FET QuComm project.

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Author notes

  1. Paul G. Kwiat

    Present address: Department of Physics, University of Illinois, Urbana-Champaign, 1110 West Green Street, Urbana, Illinois, 61801-3080, USA

  2. Salvador Barraza-Lopez

    Present address: Escuela Superior de Física y Matemáticas, IPN, Mexico D.F., 07738, Mexico

Authors and Affiliations

  1. Physics Division, P-23, Los Alamos National Laboratory, Los Alamos, 87545, New Mexico, USA

    Paul G. Kwiat & Salvador Barraza-Lopez

  2. Group of Applied Physics, University of Geneva, Geneva, 4 1211, Switzerland

    André Stefanov & Nicolas Gisin

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  1. Paul G. Kwiat
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  4. Nicolas Gisin
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Correspondence to Paul G. Kwiat.

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Kwiat, P., Barraza-Lopez, S., Stefanov, A. et al. Experimental entanglement distillation and ‘hidden’ non-locality. Nature 409, 1014–1017 (2001). https://doi.org/10.1038/35059017

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