Preparation and storage of frequency-uncorrelated entangled photons from cavity-enhanced spontaneous parametric downconversion


The preparation and storage of photonic entanglement are central to the achievement of scalable linear optical quantum computation1,2,3 (LOQC). The most widely used photonic entanglement source (a spontaneous parametric downconversion (SPDC) source)4,5 is not directly suitable for storage, because its working frequency bandwidth is significantly larger than any available quantum memory. To remedy this problem, cavity-enhanced narrow-band SPDC sources6,7,8,9,10,11,12 have been developed. However, the storage of cavity-enhanced narrow-band entangled photons has not yet been achieved. Also, the spectral correlations between the entangled photons can make them practically useless for scalable LOQC5,13,14. Here, we report the preparation and storage of frequency-uncorrelated narrowband (5 MHz) entangled photons from a cavity-enhanced SPDC source. The frequency correlation between the entangled photons is eliminated by changing the continuous UV pumping beam to short pulses. The storage of the polarization state of a single photon, and of a photon entangled with another flying in the fibre, is demonstrated. Our work demonstrates a quantum interface between narrow-band entangled photons from cavity SPDC and atomic quantum memory, and thus provides an important tool towards the achievement of all-optical quantum information processing.

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Figure 1: Experimental set-up.
Figure 2: Characterizations of storage medium.
Figure 3: Performance of the quantum memory.


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This work was supported by the National Natural Science Foundation of China, the National Fundamental Research Program of China (grant no. 2011CB921300), the Chinese Academy of Sciences, the Austrian Science Fund, the European Commission through the European Research Council Grant and the Specific Targeted Research Projects of Hybrid Information Processing.

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X-M.J., J.Y., H.Z., Z.-B.C., Y-J.D., X-H.B, S.C., B.Z. and J-W.P. designed the experiment. H.Z., X-M.J., J.Y., H-N.D., S-J.Y., T-M.Z., J.R., Y.H., X.J., F.Y., G-S.P., Z-S.Y. and S.C. performed the experiment and analysed the data. X-M.J., J.Y., H.Z., Y-J.D., X-H.B, B.Z. and J-W.P. edited the manuscript.

Corresponding authors

Correspondence to Bo Zhao or Jian-Wei Pan.

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The authors declare no competing financial interests.

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Zhang, H., Jin, XM., Yang, J. et al. Preparation and storage of frequency-uncorrelated entangled photons from cavity-enhanced spontaneous parametric downconversion. Nature Photon 5, 628–632 (2011).

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