近日，德国马克斯-普朗克量子光学研究所的Olivier Morin及其研究团队取得一项新进展。经过不懈努力，他们实现确定性生成光子图态的融合。相关研究成果已于2024年5月8日在国际权威学术期刊《自然》上发表。

据悉，纠缠已经从量子物理学的一个谜一般的概念发展成为量子技术的一个关键组成部分。它解释了与经典物理学相矛盾的测量结果之间的联系，而且在量子比特的小规模集合中得到了深入的探索。在基于门的量子计算协议中，构建的多体纠缠态从更宏观的视角来看，被视为基于测量的量子信息处理的关键资源。这种处理方式依赖于预先生成、用图形描述的多量子比特纠缠态。

尽管如贝尔态或线性簇态这样的小型图态已经能够通过光子产生，但为了满足日益增长的量子计算和量子网络应用需求，需要一种可编程的方法，将这些小规模的纠缠态融合成更大、更强大的状态。

该研究团队通过利用包含两个独立可寻址原子的光学谐振器实现了这一目标。环形和树形图态最多有8个量子比特，其名称反映纠缠拓扑，有效地融合了单个原子发射的光子态。融合过程本身在两个原子之间使用一个腔辅助门。原则上，该研究提出的技术可以扩展到更大数量的量子比特，更是未来构建无记忆量子中继器、实现量子互联网的关键一步。

附：英文原文

Title: Fusion of deterministically generated photonic graph states

Author: Thomas, Philip, Ruscio, Leonardo, Morin, Olivier, Rempe, Gerhard

Issue&Volume: 2024-05-08

Abstract: Entanglement has evolved from an enigmatic concept of quantum physics to a key ingredient of quantum technology. It explains correlations between measurement outcomes that contradict classical physics and has been widely explored with small sets of individual qubits. Multi-partite entangled states build up in gate-based quantum-computing protocols and—from a broader perspective—were proposed as the main resource for measurement-based quantum-information processing. The latter requires the ex-ante generation of a multi-qubit entangled state described by a graph. Small graph states such as Bell or linear cluster states have been produced with photons, but the proposed quantum-computing and quantum-networking applications require fusion of such states into larger and more powerful states in a programmable fashion. Here we achieve this goal by using an optical resonator containing two individually addressable atoms. Ring and tree graph states with up to eight qubits, with the names reflecting the entanglement topology, are efficiently fused from the photonic states emitted by the individual atoms. The fusion process itself uses a cavity-assisted gate between the two atoms. Our technique is, in principle, scalable to even larger numbers of qubits and is the decisive step towards, for instance, a memory-less quantum repeater in a future quantum internet.

DOI: 10.1038/s41586-024-07357-5

Source: https://www.nature.com/articles/s41586-024-07357-5