Wei Kejin, Tischler Nora, Zhao Si-Ran, Li Yu-Huai, Arrazola Juan Miguel, Liu Yang, Zhang Weijun, Li Hao, You Lixing, Wang Zhen, Chen Yu-Ao, Sanders Barry C, Zhang Qiang, Pryde Geoff J, Xu Feihu, Pan Jian-Wei
Shanghai Branch, Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Shanghai 201315, China.
CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China.
Phys Rev Lett. 2019 Mar 29;122(12):120504. doi: 10.1103/PhysRevLett.122.120504.
Finding exponential separation between quantum and classical information tasks is like striking gold in quantum information research. Such an advantage is believed to hold for quantum computing but is proven for quantum communication complexity. Recently, a novel quantum resource called the quantum switch-which creates a coherent superposition of the causal order of events, known as quantum causality-has been harnessed theoretically in a new protocol providing provable exponential separation. We experimentally demonstrate such an advantage by realizing a superposition of communication directions for a two-party distributed computation. Our photonic demonstration employs d-dimensional quantum systems, qudits, up to d=2^{13} dimensions and demonstrates a communication complexity advantage, requiring less than (0.696±0.006) times the communication of any causally ordered protocol. These results elucidate the crucial role of the coherence of communication direction in achieving the exponential separation for the one-way processing task, and open a new path for experimentally exploring the fundamentals and applications of advanced features of indefinite causal structures.
在量子信息研究中，找到量子与经典信息任务之间的指数级差距就如同淘到了金子。人们认为这种优势在量子计算中成立，但在量子通信复杂性方面已得到证明。最近，一种名为量子开关的新型量子资源——它能创建事件因果顺序的相干叠加，即所谓的量子因果性——已在一种新协议中得到理论应用，该协议实现了可证明的指数级差距。我们通过实现两方分布式计算中通信方向的叠加，在实验上证明了这种优势。我们的光子学演示使用了高达(d = 2^{13})维的(d)维量子系统，即量子位，并展示了通信复杂性优势，所需通信量不到任何因果有序协议的((0.696±0.006))倍。这些结果阐明了通信方向的相干性在实现单向处理任务的指数级差距中所起的关键作用，并为实验探索不确定因果结构的高级特性的基本原理和应用开辟了一条新途径。
