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Quantum Information

Source of triggered entangled photon pairs? (Reply)


We have reported triggered photon-pair emission from single quantum dots that is suggestive of polarization entanglement1. Gilchrist et al.2 criticize our analysis of the density matrix, claiming that the entanglement test is inappropriate. However, we show here that this analysis is in fact valid for an unpolarized source such as ours, and that this analysis (as well as alternative measures of entanglement) suggests that quantum-dot sources do emit entangled photons, and that their quality is rapidly improving3.

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Figure 1: Measurements showing that emission is unpolarized, within error.


  1. Stevenson, R. M. et al. Nature 439, 179–182 (2006).

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  2. Gilchrist, A., Resch, K. J. & White, A. G. Nature 445, doi: 10.1038/nature05546 (2007).

  3. Young, R. J. et al. N. J. Physics 8, 29 (2006).

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  4. Edamatsu, K., Oohata, G., Shimizu, R. & Itoh, T. Nature 431, 167–170 (2004).

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Correspondence to R. Mark Stevenson.

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Stevenson, R., Young, R., Atkinson, P. et al. Source of triggered entangled photon pairs? (Reply). Nature 445, E5–E6 (2007).

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