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# Observation of eight-photon entanglement

## Abstract

The creation of increasingly large multipartite entangled states is not only a fundamental scientific endeavour in itself1,2,3, but is also the enabling technology for quantum information4,5. Tremendous experimental effort has been devoted to generating multiparticle entanglement with a growing number of qubits6,7,8,9,10,11,12,13,14,15,16. So far, up to six spatially separated single photons10,11,12,13,14 have been entangled based on parametric downconversion17. Multiple degrees of freedom of a single photon have been exploited to generate forms of hyper-entangled states18,19. Here, using new ultra-bright sources of entangled photon pairs20, an eight-photon interferometer and post-selection detection, we demonstrate for the first time the creation of an eight-photon Schrödinger cat state1 with genuine multipartite entanglement. The ability to control eight individual photons represents a step towards optical quantum computation, and will enable new experiments on, for example, quantum simulation21,22, topological error correction23 and testing entanglement dynamics under decoherence24.

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## References

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## Acknowledgements

The authors thank M. Cramer for useful discussions. This work was supported by the National Natural Science Foundation of China, the Chinese Academy of Sciences and the National Fundamental Research Program (grant no. 2011CB921300).

## Author information

Authors

### Contributions

X.-C.Y., X.-H.B., Y.-A.C. and J.-W.P. conceived and designed the research. X.-C.Y., T.-X.W., P.X., H.L., G.-S.P. and C.-Z.P. carried out the experiment. X.-H.B. programmed the FPGA logic. C.-Y.L. contributed theoretical analysis tools. X.-C.Y. and Y.-A.C. analysed the data. X.-C.Y., C.-Y.L., Y.-A.C. and J.-W.P. wrote the manuscript. C.-Y.L., Y.-A.C. and J.-W.P. supervised the project.

### Corresponding authors

Correspondence to Chao-Yang Lu or Jian-Wei Pan.

## Ethics declarations

### Competing interests

The authors declare no competing financial interests.

## Supplementary information

### Supplementary information

Supplementary information (PDF 229 kb)

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Yao, XC., Wang, TX., Xu, P. et al. Observation of eight-photon entanglement. Nature Photon 6, 225–228 (2012). https://doi.org/10.1038/nphoton.2011.354

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• DOI: https://doi.org/10.1038/nphoton.2011.354

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