Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei, 230026, P. R. China.
Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, 230026, P. R. China.
Nat Commun. 2018 Apr 12;9(1):1414. doi: 10.1038/s41467-018-03849-x.
Collective measurements on identically prepared quantum systems can extract more information than local measurements, thereby enhancing information-processing efficiency. Although this nonclassical phenomenon has been known for two decades, it has remained a challenging task to demonstrate the advantage of collective measurements in experiments. Here, we introduce a general recipe for performing deterministic collective measurements on two identically prepared qubits based on quantum walks. Using photonic quantum walks, we realize experimentally an optimized collective measurement with fidelity 0.9946 without post selection. As an application, we achieve the highest tomographic efficiency in qubit state tomography to date. Our work offers an effective recipe for beating the precision limit of local measurements in quantum state tomography and metrology. In addition, our study opens an avenue for harvesting the power of collective measurements in quantum information-processing and for exploring the intriguing physics behind this power.
集体测量相同制备的量子系统可以提取比局部测量更多的信息，从而提高信息处理效率。尽管这种非经典现象已经为人所知二十年，但在实验中证明集体测量的优势仍然是一项具有挑战性的任务。在这里，我们引入了一种基于量子行走的对两个相同制备的量子比特进行确定性集体测量的通用方案。我们使用光子量子行走，在没有后选择的情况下实验上实现了保真度为 0.9946 的优化集体测量。作为应用，我们在量子态层析成像中实现了迄今为止最高的层析效率。我们的工作为在量子态层析成像和计量学中超越局部测量的精度极限提供了有效的方案。此外，我们的研究为在量子信息处理中利用集体测量的优势以及探索这种优势背后的有趣物理提供了途径。
