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Experimental high-dimensional two-photon entanglement and violations of generalized Bell inequalities

Abstract

Quantum entanglement1,2 plays a vital role in many quantum-information and communication tasks3. Entangled states of higher-dimensional systems are of great interest owing to the extended possibilities they provide. For example, they enable the realization of new types of quantum information scheme that can offer higher-information-density coding and greater resilience to errors than can be achieved with entangled two-dimensional systems (see ref. 4 and references therein). Closing the detection loophole in Bell test experiments is also more experimentally feasible when higher-dimensional entangled systems are used5. We have measured previously untested correlations between two photons to experimentally demonstrate high-dimensional entangled states. We obtain violations of Bell-type inequalities generalized to d-dimensional systems6 up to d=12. Furthermore, the violations are strong enough to indicate genuine 11-dimensional entanglement. Our experiments use photons entangled in orbital angular momentum7, generated through spontaneous parametric down-conversion8,9, and manipulated using computer-controlled holograms.

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Figure 1: Schematic representation of experimental set-up for violations of Bell-type inequalities.
Figure 2: Coincidence count rate (self-normalized) as a function of the relative orientation angle between state analysers (θAθB).
Figure 3: Experimental Bell-type parameter Sd versus number of dimensions d.
Figure 4: Experimental coincidence rates proportional to the probability of measuring the state with ℓs,ℓi=−5,…,+5.

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Acknowledgements

We acknowledge suggestions from S. M. Barnett. This work was funded by the Engineering and Physical Sciences Research Council (EPSRC). A.C.D. acknowledges funding support from the Scottish Universities Physics Alliance (SUPA).

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Contributions

A.C.D. and E.A. devised the concept of the experiment. E.A. supervised the theoretical aspects of the project. G.S.B. and M.J.P. advised on aspects of experimental design. A.C.D. and J.L. carried out the experiment. A.C.D. and E.A. wrote the paper with contributions from all authors.

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Correspondence to Adetunmise C. Dada.

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The authors declare no competing financial interests.

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Dada, A., Leach, J., Buller, G. et al. Experimental high-dimensional two-photon entanglement and violations of generalized Bell inequalities. Nature Phys 7, 677–680 (2011). https://doi.org/10.1038/nphys1996

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