Polarization-entangled photons produced with high-symmetry site-controlled quantum dots

  • A Retraction to this article was published on 16 October 2012


Efficient sources of entangled photons ‘on demand’ are crucial for the development of quantum information technology1. Such sources cannot rely on parametric down-conversion techniques because they generate entangled pairs with Poissonian statistics2. Biexciton–exciton decays in semiconductor quantum dots have been proposed3 and demonstrated4,5,6 as a source of triggered polarization-entangled photons, but their efficiency is limited by the fine-structure splitting of exciton transitions due to low quantum dot symmetry7. Here, we report on the generation of entangled photons from highly symmetric, site-controlled quantum dots grown in inverted pyramids8,9. Polarization entanglement is demonstrated by measurements of the two-photon density matrix and the confirmation of several entanglement criteria. The unique symmetry and exceptional uniformity of the pyramidal quantum dots provide significant potential for producing sources of triggered entangled photons from as-grown quantum dots without resorting to any of the post-processing steps customarily used in previous studies10.

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Figure 1: Pyramidal quantum dots: structure and optical spectra.
Figure 2: Linearly polarized photoluminescence spectra from two different QDs.
Figure 3: Signatures of 2X–X photon entanglement.
Figure 4: Entanglement evaluation.


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This work was supported by the Swiss National Foundation under the National Centre of Competence in Research (NCCR) project Quantum Photonics. The authors also acknowledge fruitful discussions with R.J. Young.

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A.M. carried out the optical experiments. A.M., M.F. and E.K. analysed the data. A.M., P.G. and B.D. were involved in the fabrication of the samples. P.G. and A.R. performed MOCVD growth of the samples. A.M., M.F., P.G. and E.K. wrote the manuscript. The work was supervised by J.F. and E.K. All authors discussed the results and commented on the manuscript.

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Correspondence to A. Mohan.

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Mohan, A., Felici, M., Gallo, P. et al. Polarization-entangled photons produced with high-symmetry site-controlled quantum dots. Nature Photon 4, 302–306 (2010). https://doi.org/10.1038/nphoton.2010.2

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