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arXiv 1609.09653quant-ph
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在无量子态层析的纠缠交换装置中测量Bell非定域性和全纠缠分数

Bell nonlocality and fully-entangled fraction measured in an entanglement-swapping device without quantum state tomography

Karol Bartkiewicz, Karel Lemr, Antonín Černoch, Adam Miranowicz

摘要:

我们展示了一个有效的实验程序的基础上纠缠交换,以确定贝尔非局域性测量Horodecki等人。A 200,340(1995)]和Bennett等人[Phys.Rev.A54,3824(1996)]的任意两量子比特偏振编码态的完全纠缠部分。的非局部性措施对应于违反的Clauser-Horne-Shimony-Holt(CHSH)在所有测量设置优化的量。通过同时使用给定状态的两个副本,我们只直接测量六个参数。我们的方法既不需要15个参数的完整量子态层析成像,也不需要连续扫描通常的CHSH不等式测试中双方使用的测量基,每个优化步骤中有四个测量。我们分析了任意两量子比特态的Bell非定域性和其他纠缠见证(包括完全纠缠分数和非线性熵见证)的测量程度如何能够估计其纠缠。特别是,我们测量了这些证人,并估计了各种两量子位维尔纳态的负性。我们的方法对于基于纠缠交换的量子通信协议特别有用。

英文摘要:

We demonstrate an efficient experimental procedure based on entanglement swapping to determine the Bell nonlocality measure of Horodecki et al. [Phys. Lett. A 200, 340 (1995)] and the fully-entangled fraction of Bennett et al. [Phys. Rev. A 54, 3824 (1996)] of an arbitrary two-qubit polarization-encoded state. The nonlocality measure corresponds to the amount of the violation of the Clauser-Horne-Shimony-Holt (CHSH) optimized over all measurement settings. By using simultaneously two copies of a given state, we measure directly only six parameters. Our method requires neither full quantum state tomography of 15 parameters nor continuous scanning of the measurement bases used by two parties in the usual CHSH inequality tests with four measurements in each optimization step. We analyze how well the measured degrees of Bell nonlocality and other entanglement witnesses (including the fully-entangled fraction and a nonlinear entropic witness) of an arbitrary two-qubit state can estimate its entanglement. In particular, we measured these witnesses and estimated the negativity of various two-qubit Werner states. Our approach could especially be useful for quantum communication protocols based on entanglement swapping.

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