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Observation of entanglement between a quantum dot spin and a single photon

Abstract

Entanglement has a central role in fundamental tests of quantum mechanics1 as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, a main challenge is the efficient generation of entanglement between stationary (spin) and propagating (photon) quantum bits2. Here we report the observation of quantum entanglement between a semiconductor quantum dot spin and the colour of a propagating optical photon. The demonstration of entanglement relies on the use of fast, single-photon detection, which allows us to project the photon into a superposition of red and blue frequency components. Our results extend the previous demonstrations of single-spin/single-photon entanglement in trapped ions3, neutral atoms4,5 and nitrogen–vacancy centres6 to the domain of artificial atoms in semiconductor nanostructures that allow for on-chip integration of electronic and photonic elements7,8. As a result of its fast optical transitions and favourable selection rules, the scheme we implement could in principle generate nearly deterministic entangled spin–photon pairs at a rate determined ultimately by the high spontaneous emission rate. Our observation constitutes a first step towards implementation of a quantum network with nodes9 consisting of semiconductor spin quantum bits10,11,12.

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Figure 1: Quantum dot transitions and experimental set-up.
Figure 2: Measurement of classical spin–photon correlations.
Figure 3: Demonstration of quantum correlation between the electron spin and the emitted single-photon pulse.

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Acknowledgements

We acknowledge discussions with W. Chin, M. Kroner, A. Srivastava, J. Elzerman, A. Reinhard, T. Volz, P. Maletinsky and D. Gershoni. This work is supported by NCCR Quantum Science and Technology, a research instrument of the Swiss National Science Foundation; the Swiss NSF (grant no. 200021-140818); an ERC Advanced Investigator Grant (A.I.); and a Marie Curie International Incoming Fellowship within FP7 (W.B.G.).

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Correspondence to W. B. Gao or A. Imamoglu.

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Gao, W., Fallahi, P., Togan, E. et al. Observation of entanglement between a quantum dot spin and a single photon. Nature 491, 426–430 (2012). https://doi.org/10.1038/nature11573

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