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# Quantum entanglement between an optical photon and a solid-state spin qubit

## Abstract

Quantum entanglement is among the most fascinating aspects of quantum theory1. Entangled optical photons are now widely used for fundamental tests of quantum mechanics2 and applications such as quantum cryptography1. Several recent experiments demonstrated entanglement of optical photons with trapped ions3, atoms4,5 and atomic ensembles6,7,8, which are then used to connect remote long-term memory nodes in distributed quantum networks9,10,11. Here we realize quantum entanglement between the polarization of a single optical photon and a solid-state qubit associated with the single electronic spin of a nitrogen vacancy centre in diamond. Our experimental entanglement verification uses the quantum eraser technique5,12, and demonstrates that a high degree of control over interactions between a solid-state qubit and the quantum light field can be achieved. The reported entanglement source can be used in studies of fundamental quantum phenomena and provides a key building block for the solid-state realization of quantum optical networks13,14.

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## References

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## Acknowledgements

We thank F. Jelezko, J. Wrachtrup, V. Jacques, N. Manson, J. Taylor and J. MacArthur for discussions and experimental help. This work was supported by the Defense Advanced Research Projects Agency, NSF, Harvard-MIT CUA, the NDSEG Fellowship and the Packard Foundation. The content of the information does not necessarily reflect the position or the policy of the US Government, and no official endorsements should be inferred.

## Author information

Authors

### Contributions

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

### Corresponding author

Correspondence to M. D. Lukin.

## Ethics declarations

### Competing interests

The authors declare no competing financial interests.

## Supplementary information

### Supplementary Information

This file contains 1 Supplementary Methods, 2 Level structure and polarization properties of the NV centre, 3 Spin readout, 4 Verification of polarization selection rules for A2 state, 5 Effects of magnetic environment, detunings, and echo, 6 Fidelity estimates, Supplementary Figures S1-S7 with legends and References. (PDF 1003 kb)

## Rights and permissions

Reprints and Permissions

Togan, E., Chu, Y., Trifonov, A. et al. Quantum entanglement between an optical photon and a solid-state spin qubit. Nature 466, 730–734 (2010). https://doi.org/10.1038/nature09256

• Accepted:

• Issue Date:

• DOI: https://doi.org/10.1038/nature09256

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