Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Experimental nested purification for a linear optical quantum repeater


Quantum repeaters1,2,3,4 are essential elements for demonstrating global-scale quantum communication. Over the past few decades, tremendous efforts have been dedicated to implementing a practical quantum repeater5,6,7,8,9,10. However, nested purification1, the backbone of a quantum repeater, remains a challenge because the capacity for successive entanglement manipulation is still absent. Here, we propose and demonstrate an architecture of nested purification using spontaneous parametric downconversion sources11. A heralded entangled photon pair with higher fidelity is successfully purified from two copies of low-fidelity pairs that experience entanglement swapping and noisy channels. By delicately designing the optical circuits, double-pair emission noise is eliminated automatically and the purified state can be used for scalable entanglement connections to extend the communication distance. Combined with a quantum memory, our approach can be applied immediately in the implemention of a practical quantum repeater.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1
Fig. 2: Experimental set-up for nested purification.
Fig. 3: Experimental results.


  1. Briegel, H., Dur, W., Cirac, J. & Zoller, P. Quantum repeaters: the role of imperfect local operations in quantum communication. Phys. Rev. Lett. 81, 5932–5935 (1998).

    Article  ADS  Google Scholar 

  2. Dur, W., Briegel, H., Cirac, J. & Zoller, P. Quantum repeaters based on entanglement purification. Phys. Rev. A 59, 169–181 (1999).

    Article  ADS  MATH  Google Scholar 

  3. Duan, L., Lukin, M., Cirac, J. & Zoller, P. Long-distance quantum communication with atomic ensembles and linear optics. Nature 414, 413–418 (2001).

    Article  ADS  Google Scholar 

  4. Muralidharan, S., Kim, J., Lütkenhaus, N., Lukin, M. D. & Jiang, L. Ultrafast and fault-tolerant quantum communication across long distances. Phys. Rev. Lett. 112, 250501 (2014).

    Article  ADS  Google Scholar 

  5. Moehring, D. et al. Entanglement of single-atom quantum bits at a distance. Nature 449, 68–71 (2007).

    Article  ADS  Google Scholar 

  6. Chou, C.-W. et al. Functional quantum nodes for entanglement distribution over scalable quantum networks. Science 316, 1316–1320 (2007).

    Article  ADS  Google Scholar 

  7. Yuan, Z.-S. et al. Experimental demonstration of a BDCZ quantum repeater node. Nature 454, 1098–1101 (2008).

    Article  ADS  Google Scholar 

  8. Lee, K. C. et al. Entangling macroscopic diamonds at room temperature. Science 334, 1253–1256 (2011).

    Article  ADS  Google Scholar 

  9. Hofmann, J. et al. Heralded entanglement between widely separated atoms. Science 337, 72–75 (2012).

    Article  ADS  Google Scholar 

  10. Bernien, H. et al. Heralded entanglement between solid-state qubits separated by three metres. Nature 497, 86–90 (2013).

    Article  ADS  Google Scholar 

  11. Kwiat, P. G. et al. New high-intensity source of polarization-entangled photon pairs. Phys. Rev. Lett. 75, 4337–4341 (1995).

    Article  ADS  Google Scholar 

  12. Liu, Y. et al. Decoy-state quantum key distribution with polarized photons over 200 km. Opt. Express 18, 8587–8594 (2010).

    Article  ADS  Google Scholar 

  13. Wang, S. et al. 2 GHz clock quantum key distribution over 260 km of standard telecom fiber. Opt. Lett. 37, 1008–1010 (2012).

    Article  ADS  Google Scholar 

  14. Korzh, B. et al. Provably secure and practical quantum key distribution over 307 km of optical fibre. Nat. Photon. 9, 163–168 (2015).

    Article  ADS  Google Scholar 

  15. Zukowski, M., Zeilinger, A., Horne, M. & Ekert, A. Event-ready-detectors Bell experiment via entanglement swapping. Phys. Rev. Lett. 71, 4287–4290 (1993).

    Article  ADS  Google Scholar 

  16. Tang, Y.-L. et al. Measurement-device-independent quantum key distribution over 200 km. Phys. Rev. Lett. 114, 069901 (2015).

    Article  ADS  Google Scholar 

  17. Yin, H.-L. et al. Measurement-device-independent quantum key distribution over a 404 km optical fiber. Phys. Rev. Lett. 117, 190501 (2016).

    Article  ADS  Google Scholar 

  18. Bennett, C. et al. Purification of noisy entanglement and faithful teleportation via noisy channels. Phys. Rev. Lett. 76, 722–725 (1996).

    Article  ADS  Google Scholar 

  19. Pan, J., Simon, C., Brukner, C. & Zeilinger, A. Entanglement purification for quantum communication. Nature 410, 1067–1070 (2001).

    Article  ADS  Google Scholar 

  20. Pan, J., Bouwmeester, D., Weinfurter, H. & Zeilinger, A. Experimental entanglement swapping: entangling photons that never interacted. Phys. Rev. Lett. 80, 3891–3894 (1998).

    Article  ADS  MATH  MathSciNet  Google Scholar 

  21. Pan, J., Gasparoni, S., Ursin, R., Weihs, G. & Zeilinger, A. Experimental entanglement purification of arbitrary unknown states. Nature 423, 417–422 (2003).

    Article  ADS  Google Scholar 

  22. Jennewein, T., Weihs, G., Pan, J.-W. & Zeilinger, A. Experimental nonlocality proof of quantum teleportation and entanglement swapping. Phys. Rev. Lett. 88, 017903 (2001).

    Article  ADS  Google Scholar 

  23. De Riedmatten, H. et al. Long-distance entanglement swapping with photons from separated sources. Phys. Rev. A 71, 050302 (2005).

    Article  Google Scholar 

  24. Halder, M. et al. Entangling independent photons by time measurement. Nat. Phys. 3, 692–695 (2007).

    Article  Google Scholar 

  25. Goebel, A. M. et al. Multistage entanglement swapping. Phys. Rev. Lett. 101, 080403 (2008).

    Article  ADS  Google Scholar 

  26. Yao, X.-C. et al. Observation of eight-photon entanglement. Nat. Photon. 6, 225–228 (2012).

    Article  ADS  Google Scholar 

  27. Kim, Y.-H., Kulik, S. P., Chekhova, M. V., Grice, W. P. & Shih, Y. Experimental entanglement concentration and universal Bell-state synthesizer. Phys. Rev. A 67, 010301 (2003).

    Article  ADS  Google Scholar 

  28. Zhao, B., Chen, Z.-B., Chen, Y.-A., Schmiedmayer, J. & Pan, J.-W. Robust creation of entanglement between remote memory qubits. Phys. Rev. Lett. 98, 240502 (2007).

    Article  ADS  Google Scholar 

  29. Chen, Z.-B., Zhao, B., Chen, Y.-A., Schmiedmayer, J. & Pan, J.-W. Fault-tolerant quantum repeater with atomic ensembles and linear optics. Phys. Rev. A 76, 022329 (2007).

    Article  ADS  Google Scholar 

  30. Sangouard, N., Simon, C., de Riedmatten, H. & Gisin, N. Quantum repeaters based on atomic ensembles and linear optics. Rev. Mod. Phys. 83, 33–80 (2011).

    Article  ADS  Google Scholar 

  31. Grice, W. P., U’Ren, A. B. & Walmsley, I. A. Eliminating frequency and space–time correlations in multiphoton states. Phys. Rev. A 64, 063815 (2001).

    Article  ADS  Google Scholar 

  32. Dixon, P. B. et al. Heralding efficiency and correlated-mode coupling of near-IR fiber-coupled photon pairs. Phys. Rev. A 90, 043804 (2014).

    Article  ADS  Google Scholar 

  33. Marsili, F. et al. Detecting single infrared photons with 93% system efficiency. Nat. Photon. 7, 210–214 (2013).

    Article  ADS  Google Scholar 

  34. Lita, A. E., Miller, A. J. & Nam, S. W. Counting near-infrared single-photons with 95% efficiency. Opt. Express 16, 3032–3040 (2008).

    Article  ADS  Google Scholar 

Download references


This work was supported by the National Natural Science Foundation of China (grants nos. 11274292, 11374284, 11425417, 11521063 and 61625503), the National Fundamental Research Program (grants nos. 2013CB336800 and 2013CB922001) and the Chinese Academy of Sciences.

Author information

Authors and Affiliations



B.Z., Y.-A.C. and J.-W.P. conceived and designed the experiments. L.-K.C., P.X. and X.-C.Y. designed and characterized the multiphoton optical circuits. H.-L.Y. and C.L. developed the feedback system. T.X., Z.-D.L., H.L., N.-L.L., L.L., T.Y. and C.-Z.P. provided experimental assistance. L.-K.C., H.-L.Y., P.X., T.X. and Z.D-.L. collected and analysed the data. L.-K.C., X.-C.Y., B.Z., Y.-A.C. and J.-W.P. wrote the manuscript, with input from all authors. N.-L.L., Y.-A.C. and J.-W.P. supervised the project.

Corresponding authors

Correspondence to Bo Zhao, Yu-Ao Chen or Jian-Wei Pan.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Electronic supplementary material

Supplementary Information

Supplementary material

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Chen, LK., Yong, HL., Xu, P. et al. Experimental nested purification for a linear optical quantum repeater. Nature Photon 11, 695–699 (2017).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing