Entanglement of spin waves among four quantum memories

Article metrics


Quantum networks are composed of quantum nodes that interact coherently through quantum channels, and open a broad frontier of scientific opportunities1. For example, a quantum network can serve as a ‘web’ for connecting quantum processors for computation2,3 and communication4, or as a ‘simulator’ allowing investigations of quantum critical phenomena arising from interactions among the nodes mediated by the channels5,6. The physical realization of quantum networks generically requires dynamical systems capable of generating and storing entangled states among multiple quantum memories, and efficiently transferring stored entanglement into quantum channels for distribution across the network. Although such capabilities have been demonstrated for diverse bipartite systems7,8,9,10,11,12, entangled states have not been achieved for interconnects capable of ‘mapping’ multipartite entanglement stored in quantum memories to quantum channels. Here we demonstrate measurement-induced entanglement stored in four atomic memories; user-controlled, coherent transfer of the atomic entanglement to four photonic channels; and characterization of the full quadripartite entanglement using quantum uncertainty relations13,14,15,16. Our work therefore constitutes an advance in the distribution of multipartite entanglement across quantum networks. We also show that our entanglement verification method is suitable for studying the entanglement order of condensed-matter systems in thermal equilibrium17,18.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Overview of the experiment.
Figure 2: Quadripartite entanglement among four atomic ensembles.
Figure 3: Dissipative dynamics of atomic entanglement.


  1. 1

    Kimble, H. J. The quantum internet. Nature 453, 1023–1030 (2008)

  2. 2

    Preskill, J. Quantum computation. Phys. 219 Course Inf.http://www.theory.caltech.edu/people/preskill/ph219/#lecture〉 (1997)

  3. 3

    Nielsen, M. A. & Chuang, I. L. Quantum Computation and Quantum Information (Cambridge Univ. Press, 2000)

  4. 4

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

  5. 5

    Lloyd, S. Universal quantum simulator. Science 273, 1073–1078 (1996)

  6. 6

    Acín, A., Cirac, J. I. & Lewenstein, M. Entanglement percolation in quantum networks. Nature Phys. 3, 256–259 (2007)

  7. 7

    Chou, C. W. et al. Measurement-induced entanglement for excitation stored in remote atomic ensembles. Nature 438, 828–832 (2005)

  8. 8

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

  9. 9

    Simon, J., Tanji, H., Ghosh, S. & Vuletic´, V. Single-photon bus connecting spin-wave quantum memories. Nature Phys. 3, 765–769 (2007)

  10. 10

    Weber, B. et al. Photon-photon entanglement with a single trapped atom. Phys. Rev. Lett. 102, 030501 (2009)

  11. 11

    Choi, K. S., Deng, H., Laurat, J. & Kimble, H. J. Mapping photonic entanglement into and out of a quantum memory. Nature 452, 67–71 (2008)

  12. 12

    Jost, J. D. et al. Entangled mechanical oscillators. Nature 459, 683–685 (2009)

  13. 13

    Sørensen, A. & Mølmer, K. Entanglement and extreme spin squeezing. Phys. Rev. Lett. 86, 4431–4434 (2001)

  14. 14

    Hofmann, H. F. & Takeuchi, S. Violation of local uncertainty relations as a signature of entanglement. Phys. Rev. A 68, 032103 (2003)

  15. 15

    Papp, S. B. et al. Characterization of multipartite entanglement for one photon shared among four optical modes. Science 324, 764–768 (2009)

  16. 16

    Lougovski, P. et al. Verifying multipartite mode entanglement of W states. N. J. Phys. 11, 063029 (2009)

  17. 17

    Amico, L., Fazio, R., Osterloh, A. & Vedral, V. Entanglement in many-body systems. Rev. Mod. Phys. 80, 517–576 (2008)

  18. 18

    Gühne, O. & Tóth, G. Entanglement detection. Phys. Rep. 474, 1–75 (2009)

  19. 19

    Steffen, M. et al. Measurement of the entanglement of two superconducting qubits via state tomography. Science 313, 1423–1425 (2006)

  20. 20

    DiCarlo, L. et al. Demonstration of two-qubit algorithms with a superconducting quantum processor. Nature 460, 240–244 (2009)

  21. 21

    van Enk, S. J., Lütkenhaus, N. & Kimble, H. J. Experimental procedures for entanglement verification. Phys. Rev. A 75, 052318 (2007)

  22. 22

    Horodecki, R., Horodecki, P., Horodecki, M. & Horodecki, K. Quantum entanglement. Rev. Mod. Phys. 81, 865–942 (2009)

  23. 23

    Leibfried, D. et al. Creation of a six-atom ‘Schrödinger cat’ state. Nature 438, 639–642 (2005)

  24. 24

    Haffner, H. et al. Scalable multiparticle entanglement of trapped ions. Nature 438, 643–646 (2005)

  25. 25

    Aoki, T. et al. Experimental creation of a fully inseparable tripartite continuous-variable state. Phys. Rev. Lett. 91, 080404 (2003)

  26. 26

    Su, X. et al. Experimental preparation of quadripartite cluster and Greenberger-Horne-Zeilinger entangled states for continuous variables. Phys. Rev. Lett. 98, 070502 (2007)

  27. 27

    Gao, W.-B. et al. Experimental demonstration of a hyper-entangled ten-qubit Schrödinger cat state. Nature Phys. 6, 331–335 (2010)

  28. 28

    Lvovsky, A. I., Sanders, B. C. & Tittel, W. Optical quantum memory. Nature Photon. 3, 706–714 (2009)

  29. 29

    Simon, J. & Tanji, H. Thompson, J. K. & Vuletic´, V. Interfacing collective atomic excitations and single photons. Phys. Rev. Lett. 98, 183601 (2007)

  30. 30

    Heaney, L., Cabello, A., Santos, M. F. & Vedral, V. Extreme nonlocality with one photon. Preprint at 〈http://arxiv.org/abs/0911.0770v2〉 (2010)

  31. 31

    Balic´, V., Braje, D. A., Kolchin, P., Yin, G. Y. & Harris, S. E. Generation of paired photons with controllable waveforms. Phys. Rev. Lett. 94, 183601 (2005)

  32. 32

    Eisert, J., Simon, C. & Plenio, M. B. On the quantification of entanglement in infinite-dimensional quantum systems. J. Phys. A 35, 3911–3923 (2002)

  33. 33

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

  34. 34

    Laurat, J. et al. Towards experimental entanglement connection with atomic ensembles in the single excitation regime. N. J. Phys. 9, 207–220 (2007)

  35. 35

    Hammerer, K., Sorensen, A. S. & Polzik, E. S. Quantum interface between light and atomic ensembles. Rev. Mod. Phys. 82, 1041–1093 (2010)

  36. 36

    Zhao, R. et al. Long-lived quantum memory. Nature Phys. 5, 100–104 (2009)

  37. 37

    Zhao, B. et al. A millisecond quantum memory for scalable quantum networks. Nature Phys. 5, 95–99 (2009)

  38. 38

    Schnorrberger, U. et al. Electromagnetically induced transparency and light storage in an atomic Mott insulator. Phys. Rev. Lett. 103, 033003 (2009)

  39. 39

    Zhang, R., Garner, S. R. & Hau, L. V. Creation of long-term coherent optical memory via controlled nonlinear interactions in Bose-Einstein condensates. Phys. Rev. Lett. 103, 233602 (2009)

  40. 40

    Colombe, Y. et al. Strong atom-field coupling for Bose–Einstein condensates in an optical cavity on a chip. Nature 450, 272–276 (2007)

  41. 41

    Vetsch, E. et al. Optical interface created by laser-cooled atoms trapped in the evanescent field surrounding an optical nanofiber. Phys. Rev. Lett. 104, 203603 (2010)

  42. 42

    Deutsch, C. et al. Spin self-rephasing and very long coherence times in a trapped atomic ensemble. Phys. Rev. Lett. 105, 020401 (2010)

  43. 43

    Sangouard, N., Simon, C., de Riedmatten, H. & Gisin, N. Quantum repeaters based on atomic ensembles and linear optics. Preprint at 〈http://arxiv.org/abs/0906.2699v2〉 (2009)

  44. 44

    Ivanovic, I. D. How to differentiate between non-orthogonal states. Phys. Lett. A 123, 257–259 (1987)

  45. 45

    Dieks, D. Overlap and distinguishability of quantum states. Phys. Lett. A 126, 303–306 (1988)

  46. 46

    Peres, A. How to differentiate between non-orthogonal states. Phys. Lett. A 128, 19 (1988)

  47. 47

    Chefles, A. Unambiguous discrimination between linearly independent quantum states. Phys. Lett. A 239, 339–347 (1998)

Download references


We acknowledge discussions with K. Hammerer, P. Zoller and J. Ye. This research is supported by the National Science Foundation, the DOD NSSEFF program, the Northrop Grumman Corporation and the Intelligence Advanced Research Projects Activity. A.G. acknowledges support by the Nakajima Foundation. S.B.P. acknowledges support received as a fellow of the Center for Physics of Information at Caltech.

Author information

All authors contributed extensively to the research presented in this paper.

Correspondence to H. J. Kimble.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

The file contains Supplementary Text I-VII, Supplementary Figures 1-7 with legends and additional references. (PDF 2292 kb)

Supplementary Movie 1

This movie shows the 3D rendering of the entanglement parameters for the dissipative dynamics of atomic entanglement. (MOV 9941 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Choi, K., Goban, A., Papp, S. et al. Entanglement of spin waves among four quantum memories. Nature 468, 412–416 (2010) doi:10.1038/nature09568

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.