Entangling independent photons by time measurement
Entangling independent photons by time measurement
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DOI：
10.1038/nphys700
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发表时间：
2007-10-01
期刊：
影响因子：
19.6
通讯作者：
Zbinden, Hugo
中科院分区：
文献类型：
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作者：
Halder, Matthaeus;Beveratos, Alexios;Zbinden, Hugo
纠缠是量子物理学的核心，因为它的概念基础和在量子通信中的应用。值得注意的是，纠缠可以“交换”：如果我们准备两个独立的纠缠对A1-A2和B1-B2，对A1和B1的联合测量（称为“贝尔态测量”，BSM）具有将A2和B2投射到纠缠态的效果，尽管这两个粒子从未相互作用，也没有任何共同的过去（1,2）。光子对的纠缠交换已经用脉冲源进行了实验证明（3-6），其中的挑战是在BSM中实现光子的足够锐利的同步，但从未像最初提出的那样用连续波源进行过(2)。在这里，我们提出了一个实验，其中光子的相干时间超过探测器的时间分辨率。因此，光子定时可以通过探测次数获得，脉冲源可以被连续波源取代，而连续波源不需要任何同步（6,7）。这允许首次使用完全自主的源，这是向具有真正独立和远程节点的现实世界量子网络迈出的重要一步。
Entanglement is at the heart of quantum physics, both for its conceptual foundations and for applications in quantum communication. Remarkably, entanglement can be 'swapped': if we prepare two independent entangled pairs A1-A2 and B1-B2, a joint measurement on A1 and B1 ( alled a 'Bell-state measurement', BSM) has the effect of projecting A2 and B2 onto an entangled state, although these two particles have never interacted nor share any common past(1,2). Entanglement swapping with photon pairs has already been experimentally demonstrated(3-6) using pulsed sources - where the challenge was to achieve sufficiently sharp synchronization of the photons in the BSM - but never with continuous-wave sources, as originally proposed(2). Here, we present an experiment where the coherence time of the photons exceeds the temporal resolution of the detectors. Hence, photon timing can be obtained by the detection times, and pulsed sources can be replaced by continuous-wave sources, which do not require any synchronization(6,7). This allows for the first time the use of completely autonomous sources, an important step towards real-world quantum networks with truly independent and distant nodes.