Multi-photon entanglement in high dimensions


Forming the backbone of quantum technologies today, entanglement1,2 has been demonstrated in physical systems as diverse as photons3, ions4 and superconducting circuits5. Although steadily pushing the boundary of the number of particles entangled, these experiments have remained in a two-dimensional space for each particle. Here we show the experimental generation of the first multi-photon entangled state where both the number of particles and dimensions are greater than two. Two photons in our state reside in a three-dimensional space, whereas the third lives in two dimensions. This asymmetric entanglement structure6 only appears in multiparticle entangled states with d > 26. Our method relies on combining two pairs of photons, high-dimensionally entangled in their orbital angular momentum7. In addition, we show how this state enables a new type of ‘layered’ quantum communication protocol. Entangled states such as these serve as a manifestation of the complex dance of correlations that can exist within quantum mechanics.

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Figure 1: Schematic of the experiment.
Figure 2: Three-photon coherent superposition.
Figure 3: Witnessing genuine multipartite entanglement in high dimensions.
Figure 4: A layered quantum communication protocol.


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We thank T. Scheidl, M. Tillman, J. Handsteiner, R. Lapkiewicz, and G.B. Lemos for helpful discussions. M.M. acknowledges funding from the European Commission through a Marie Curie fellowship (OAMGHZ). M.H. acknowledges funding from the Juan de la Cierva fellowship (JCI 2012-14155), the European Commission (STREP ‘RAQUEL’) and the Spanish MINECO Project No. FIS2013-40627-P, the Generalitat de Catalunya CIRIT Project No. 2014 SGR 966, the Swiss National Science Foundation (AMBIZIONE PZ00P2_161351), and fruitful discussions at LIQUID. This project was supported by the Austrian Academy of Sciences (ÖAW), the European Research Council (SIQS Grant No. 600645 EU-FP7-ICT), the Austrian Science Fund (FWF) with SFB F40 (FOQUS).

Author information




M.M. devised the concept of the experiment, with assistance from M.K. and R.F. M.M and M.E. performed the experiment. M.H. developed the high-dimensional entanglement witness. M.M., M.E., M.K. and M.H. analysed the data. M.M. and M.H. developed the layered quantum communication protocol. A.Z. initiated the research and supervised the project. M.M. wrote the manuscript with contributions from all authors.

Corresponding author

Correspondence to Mehul Malik.

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The authors declare no competing financial interests.

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Malik, M., Erhard, M., Huber, M. et al. Multi-photon entanglement in high dimensions. Nature Photon 10, 248–252 (2016).

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