Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China.
Department of Modern Physics, University of Science and Technology of China, Hefei, China.
Nature. 2020 Feb;578(7794):240-245. doi: 10.1038/s41586-020-1976-7. Epub 2020 Feb 12.
A quantum internet that connects remote quantum processors should enable a number of revolutionary applications such as distributed quantum computing. Its realization will rely on entanglement of remote quantum memories over long distances. Despite enormous progress, at present the maximal physical separation achieved between two nodes is 1.3 kilometres, and challenges for longer distances remain. Here we demonstrate entanglement of two atomic ensembles in one laboratory via photon transmission through city-scale optical fibres. The atomic ensembles function as quantum memories that store quantum states. We use cavity enhancement to efficiently create atom-photon entanglement and we use quantum frequency conversion to shift the atomic wavelength to telecommunications wavelengths. We realize entanglement over 22 kilometres of field-deployed fibres via two-photon interference and entanglement over 50 kilometres of coiled fibres via single-photon interference. Our experiment could be extended to nodes physically separated by similar distances, which would thus form a functional segment of the atomic quantum network, paving the way towards establishing atomic entanglement over many nodes and over much longer distances.
一个连接远程量子处理器的量子互联网应该能够实现许多革命性的应用，如分布式量子计算。它的实现将依赖于远距离的远程量子存储器之间的纠缠。尽管取得了巨大的进展，但目前两个节点之间实现的最大物理分离距离是 1.3 公里，长距离的挑战仍然存在。在这里，我们通过穿过城市规模的光纤的光子传输，在一个实验室中演示了两个原子系综之间的纠缠。原子系综作为存储量子态的量子存储器。我们使用腔增强来有效地产生原子-光子纠缠，并使用量子频率转换将原子波长转换为电信波长。我们通过双光子干涉实现了 22 公里以上的现场部署光纤的纠缠，通过单光子干涉实现了 50 公里以上的螺旋光纤的纠缠。我们的实验可以扩展到物理上相隔类似距离的节点，从而形成原子量子网络的一个功能部分，为在多个节点上实现原子纠缠并实现更长的距离铺平了道路。
