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New progress: storage of photonic entanglement in atomic-ensemble quantum memories

Date: 2011-10-08
Physicists from Hefei National Laboratory for Physical Sciences at the Microscale in University of Science and Technology of China, and their colleagues from Heidelberg University and Innsbruck University, have taken a new step towards all-optical quantum information processing. They succeeded in preparing frequency-uncorrelated polarization entangled photons, and storing the photonic entanglement into a remote atomic-ensemble-based quantum memory.

Preparation and storage of frequency-uncorrelated photonic entanglement is of crucial importance to all-optical quantum information processing. As the most common photonic entanglement source, spontaneous parametric downconversion holds the promise to realize large-scale quantum computation and scalable quantum networks. Significant progress has been achieved in this regard, and narrowband SPDC photonic entanglement source, whose bandwidth matches the working bandwidth of atomic quantum memory, has been demonstrated. However, the frequency-correlation between the photon pairs severely limits the usefulness of the narrowband SPDC source in quantum information processing. Further, the storage of SPDC photons into atomic ensembles requires combing highly complex apparatus in one experiment and thus remains challenging.

In the coming issue of the scientific journal Nature Photonics, Jian-Wei Pan and his colleagues report now the preparation and storage of frequency-uncorrelated entangled photons, where narrowband frequency-uncorrelated polarization entangled photons are generated from SPDC and the photonic entanglement is stored into atomic-ensemble-based quantum memory up to 200 ns.

In the present work, the scientists find that due to the narrowband nature of the cavity, the frequency correlation between the polarization entangled photons can be eliminated by choosing a suitable short pump pulse. The elimination of frequency correlation is demonstrated in a three-photon Hong-Ou-Mandel type interference experiment. They further send one photon of the entangled pair to a memory lab 10m away and map the entanglement into and out of quantum memory by employing electromagnetic-induced-transparency. Violation of Bell’s inequality is observed up to 200 ns.

Preparation and storage of frequency-uncorrelated entangled photons from cavity-enhanced spontaneous parametric downconversion 
Han Zhang, Xian-Min Jin, Jian Yang, Han-Ning Dai, Sheng-Jun Yang, Tian-Ming Zhao, Jun Rui, Yu He, Xiao Jiang, Fan Yang, Ge-Sheng Pan, Zhen-Sheng Yuan, Youjin Deng, Zeng-Bing Chen, Xiao-Hui Bao, Shuai Chen, Bo Zhao and Jian-Wei Pan
Nature Photonics(2011)doi:10.1038/nphoton.2011.213