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Observation of micro–macro entanglement of light

Nature Physics volume 9, pages 541–544 (2013)Cite this article

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Abstract

Schrödinger’s famous thought experiment1 involves a (macroscopic) cat whose quantum state becomes entangled with that of a (microscopic) decaying nucleus. The creation of such micro–macro entanglement is being pursued in several fields, including atomic ensembles2, superconducting circuits3, electro-mechanical4 and opto-mechanical5 systems. Here we experimentally demonstrate the micro–macro entanglement of light. The macro system involves over a hundred million photons, whereas the micro system is at the single-photon level. We show that microscopic quantum fluctuations (in field quadrature measurements) on one side are correlated with macroscopic fluctuations (in the photon number statistics) on the other side. Further, we demonstrate entanglement by bringing the macroscopic state back to the single-photon level and performing full quantum state tomography of the final state. Although Schrödinger’s thought experiment was originally intended to convey the absurdity of applying quantum mechanics to macroscopic objects, this experiment and related ones suggest that it may apply on all scales.

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Figure 1: Scheme of the experiment.
Figure 2: Photon number statistics of the state in Bob’s channel that is conditionally prepared by Alice’s quadrature measurement.
Figure 3: Homodyne tomography of the micro–macro entangled state after undisplacing Bob’s mode.
Figure 4: Implementation of the set-up.

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Change history

  • 25 July 2013

    In the version of this Letter originally published online, in Fig. 1, panels b and c were transposed. This error has now been corrected in all versions of the Letter.

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Acknowledgements

The work was sponsored by NSERC, CIFAR and AITF. A.I.L. is a CIFAR Fellow. We thank N. Brunner, N. Sangouard, N. Gisin, R. Thew, S. Rahimi-Keshari, S. Raeisi and B. Sanders for helpful discussions.

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Authors and Affiliations

  1. Institute for Quantum Science and Technology and Department of Physics and Astronomy, University of Calgary, Calgary T2N 1N4, Alberta, Canada

    A. I. Lvovsky, R. Ghobadi, A. Chandra, A. S. Prasad & C. Simon

  2. Russian Quantum Center, 100 Novaya Street, Skolkovo, Moscow 143025, Russia

    A. I. Lvovsky

  3. Department of Physics, Sharif University of Technology, Tehran, Iran

    R. Ghobadi

Authors
  1. A. I. Lvovsky
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  2. R. Ghobadi
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  3. A. Chandra
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  4. A. S. Prasad
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Contributions

R.G., A.I.L. and C.S. conceived the experiment. A.I.L. performed the experiment with help from A.C. and A.S.P. A.I.L. and C.S. wrote the paper with input from A.S.P., R.G. and A.C.

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Correspondence to A. I. Lvovsky.

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The authors declare no competing financial interests.

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Lvovsky, A., Ghobadi, R., Chandra, A. et al. Observation of micro–macro entanglement of light. Nature Phys 9, 541–544 (2013). https://doi.org/10.1038/nphys2682

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