Spooky Action at a "Longer" Distance

  • [2011-11-27]

    —A New World Record of Multi-Partite Entangled States by researchers from USTC

     

    "Spooky Action at a Distance" was what Einstein used to refer to Quantum Entanglement, which means the two quanta in entanglement have mutual awareness even though they are far apart from each other. Change of one quantum renders the immediate change of the other. With the findings of researchers from Key Lab of Quantum Information in University of Science and Technology of China (USTC), the spooky action may happen at a "longer" distance as the researchers successfully generated an eight-photon Greenberger-Horne-Zeilinger state and demonstrated an eight-party quantum communication complexity scenario. It refreshes the world record and the findings are published on the Nature Communications of November 22, 2011.

    Quantum Entanglement is the basis of quantum communications. As photons have many particular advantages especially in that they are more easily transportable qubits and are more robust against decoherence, Multi-partite entangled states have become the focus and rub of researches in the field of quantum communications. Difficulty of generating Multi-partite entangled states grows as the number of quantum increase because of the probability in the nonlinear process of generating Multi-partite entangled states. The largest number of photons manipulated successfully in an experiment in the world so far is six.

    Figure 1:Setup of Linear Optics/Image by LI Chuanfeng

    The experimental group led by Prof. Chuan-Feng Li and Yun-Feng Huang adapted the beam-like entangled photon source and created two-photon entanglement source by cutting the nonlinear crystal in a special way. The creative method improve the photon detection efficiency to 25.0% with 300-mW femtosecond pulsed laser as pump. Meanwhile, the single mode optical fiber collection skill they adopted eliminated the problem of stability of light path and enhanced the entanglement of the quanta pair. The presence of genuine eight-partite entanglement was finally verified by the demonstration of an eight-photon Greenberger-Horne-Zeilinger state with a measured fidelity of 0.59, which they utilized further to accomplish an eight-party quantum communication complexity scenario.

    The achievements demonstrate that scientists have achieved an unprecedented level in generating Multi-partite entangled states with a number of eight quanta. This eight-photon entangled-state source can be applied into one-way quantum computation, quantum networks, and other quantum information processing tasks and promotes relative researches on the property and categorization of quantum entanglement. And it may be possible that the spooky action may happen at far longer distances in the future.

     

    Reference:

    Yun-Feng Huang, Bi-Heng Liu, Liang Peng, Yu-Hu Li, Li Li, Chuan-Feng Li and Guang-Can Guo, Experimental Generation of an Eight-photon Greenberger-Horne-Zeilinger State, Nature Communications 2, 546 (2011).

     

    (Key Lab of Quantum Informationof USTC, News Center of USTC, Editor: TIAN lin)
     

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