Deterministic realization of collective measurements via photonic quantum walks

Zhibo Hou, Jun-Feng Tang, Jiangwei Shang, Huangjun Zhu (), Jian Li, Yuan Yuan, Kang-Da Wu, Guo-Yong Xiang (), Chuan-Feng Li and Guang-Can Guo
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Zhibo Hou: University of Science and Technology of China, CAS
Jun-Feng Tang: University of Science and Technology of China, CAS
Jiangwei Shang: Universität Siegen
Huangjun Zhu: University of Cologne
Jian Li: Nanjing University of Posts and Telecommunications
Yuan Yuan: University of Science and Technology of China, CAS
Kang-Da Wu: University of Science and Technology of China, CAS
Guo-Yong Xiang: University of Science and Technology of China, CAS
Chuan-Feng Li: University of Science and Technology of China, CAS
Guang-Can Guo: University of Science and Technology of China, CAS

Nature Communications, 2018, vol. 9, issue 1, 1-7

Abstract: Abstract 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.

Date: 2018
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DOI: 10.1038/s41467-018-03849-x

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