In a study published online by Physical Review Letters, a research group led by Prof. GUO Guangcan, LI Chuanfeng, and XIANG Guoyong from University of Science and Technology of China (USTC) of the Chinese Academy of Sciences enhanced the performance of quantum orienteering with entangling measurements via photonic quantum walks.
In a quantum orienteering task, suppose Alice wants to communicate a random space direction to Bob, one possible means is by sending two particles with spins with its spin direction indicating the proposed direction. While no entanglement, which exists both in quantum states and quantum measurements, is between the two spins sent by Alice, it does emerge when Bob tries to encode the information. The difficulty to achieve entangling measurements has led this quantum orienteering scheme yet to be verified by experiments.
Previous studies by Prof. XIANG Guoyong's group developed a method to realize quantum entangling measurements via photonic quantum walks, and the method not only has high fidelity but also is deterministic. The researchers used this technology to achieve high efficiency in quantum state tomography, and to reduce the back action of quantum measurements in quantum thermodynamics.
In this study, the researchers used their technique of quantum walk to enhance quantum orienteering. Using photonic systems, they realized optimal entangling measurement. The experimental results demonstrated that entangling measurements can extract more direction information than local measurements, and the fidelity of antiparallel spins is 3.9% greater than that of parallel spins in orienteering, consistent with the theory proposed by Nicolas Gisin in 1999.
The study demonstrated a non-classical phenomenon that is owing to entanglement in quantum measurements instead of quantum states, and offered an effective recipe to realizing entangling measurements in photonic systems. The results are of interest not only to foundational studies of quantum entanglement and quantum measurements, but also to applications in quantum information processing.
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