Experimental determination of entanglement with a single measurement
Experimental determination of entanglement with a single measurement
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DOI：
10.1038/nature04627
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发表时间：
2006-04
期刊：
影响因子：
64.8
通讯作者：
S. Walborn;P. S. Ribeiro;L. Davidovich;F. Mintert;A. Buchleitner
中科院分区：
文献类型：
--
作者：
S. Walborn;P. S. Ribeiro;L. Davidovich;F. Mintert;A. Buchleitner
几乎所有需要共享量子信息的协议--如量子隐形传态或密钥分发--都依赖于远距离各方之间的纠缠。然而，纠缠很难用实验来表征。所有现有的技术，包括纠缠见证，或贝尔不等式，都揭示了一些量子态的纠缠，但对另一些态却是无效的；因此，它们通常不能提供令人满意的结果。这种方法从根本上不同于纠缠测量，根据定义，纠缠测量是量化任何状态下的纠缠量。然而，这些措施有一个严重的缺点，即它们通常不能在实验室实验中直接获得。在这里，我们报道了一个线性光学实验，在这个实验中，我们直接观察到了一种纯态纠缠测量，即并发。我们的测量装置包括两个量子态的副本：这两个双态是在两个光子的偏振和动量自由度中准备的，并发度是通过对其中一个光子进行单一的局部测量来测量的。
Nearly all protocols requiring shared quantum information—such as quantum teleportation or key distribution—rely on entanglement between distant parties. However, entanglement is difficult to characterize experimentally. All existing techniques for doing so, including entanglement witnesses,,or Bell inequalities, disclose the entanglement of some quantum states but fail for other states; therefore, they cannot provide satisfactory results in general. Such methods are fundamentally different from entanglement measures that, by definition, quantify the amount of entanglement in any state. However, these measures suffer from the severe disadvantage that they typically are not directly accessible in laboratory experiments. Here we report a linear optics experiment in which we directly observe a pure-state entanglement measure, namely concurrence. Our measurement set-up includes two copies of a quantum state: these ‘twin’ states are prepared in the polarization and momentum degrees of freedom of two photons, and concurrence is measured with a single, local measurement on just one of the photons.