Letter | Published:

Entanglement with negative Wigner function of almost 3,000 atoms heralded by one photon

Nature volume 519, pages 439442 (26 March 2015) | Download Citation

  • An Erratum to this article was published on 14 May 2015

Abstract

Quantum-mechanically correlated (entangled) states of many particles are of interest in quantum information, quantum computing and quantum metrology. Metrologically useful entangled states of large atomic ensembles have been experimentally realized1,2,3,4,5,6,7,8,9,10, but these states display Gaussian spin distribution functions with a non-negative Wigner quasiprobability distribution function. Non-Gaussian entangled states have been produced in small ensembles of ions11,12, and very recently in large atomic ensembles13,14,15. Here we generate entanglement in a large atomic ensemble via an interaction with a very weak laser pulse; remarkably, the detection of a single photon prepares several thousand atoms in an entangled state. We reconstruct a negative-valued Wigner function—an important hallmark of non-classicality—and verify an entanglement depth (the minimum number of mutually entangled atoms) of 2,910 ± 190 out of 3,100 atoms. Attaining such a negative Wigner function and the mutual entanglement of virtually all atoms is unprecedented for an ensemble containing more than a few particles. Although the achieved purity of the state is slightly below the threshold for entanglement-induced metrological gain, further technical improvement should allow the generation of states that surpass this threshold, and of more complex Schrödinger cat states for quantum metrology and information processing. More generally, our results demonstrate the power of heralded methods for entanglement generation, and illustrate how the information contained in a single photon can drastically alter the quantum state of a large system.

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Acknowledgements

We thank M. H. Schleier-Smith, E. S. Polzik and S. L. Christensen for discussions. This work was supported by the NSF, DARPA (QUASAR), and a MURI grant through AFOSR. S.Ć. acknowledges support from the Ministry of Education, Science and Technological Development of the Republic of Serbia, through grant numbers III45016 and OI171038.

Author information

Author notes

    • Robert McConnell
    •  & Hao Zhang

    These authors contributed equally to this work.

Affiliations

  1. Department of Physics, MIT-Harvard Center for Ultracold Atoms, and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Robert McConnell
    • , Hao Zhang
    • , Jiazhong Hu
    • , Senka Ćuk
    •  & Vladan Vuletić
  2. Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade, Serbia

    • Senka Ćuk

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Contributions

The experiment and analysis were carried out by R.M., H.Z., J.H. and S.Ć.; V.V. supervised the work; all authors discussed the results and contributed to the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Vladan Vuletić.

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DOI

https://doi.org/10.1038/nature14293

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