title: Distribution of quantum Fisher information in asymmetric cloning machines.
abstract: An unknown quantum state cannot be copied and broadcast freely due to the no-cloning theorem. Approximate cloning schemes have been proposed to achieve the optimal cloning characterized by the maximal fidelity between the original and its copies. Here, from the perspective of quantum Fisher information (QFI), we investigate the distribution of QFI in asymmetric cloning machines which produce two nonidentical copies. As one might expect, improving the QFI of one copy results in decreasing the QFI of the other copy. It is perhaps also unsurprising that asymmetric phase-covariant cloning outperforms universal cloning in distributing QFI since a priori information of the input state has been utilized. However, interesting results appear when we compare the distributabilities of fidelity (which quantifies the full information of quantum states), and QFI (which only captures the information of relevant parameters) in asymmetric cloning machines. Unlike the results of fidelity, where the distributability of symmetric cloning is always optimal for any d-dimensional cloning, we find that any asymmetric cloning outperforms symmetric cloning on the distribution of QFI for d ≤ 18, whereas some but not all asymmetric cloning strategies could be worse than symmetric ones when d > 18.
authors.affiliation: 1] College of Physics and Electronic Information, Gannan Normal University, Ganzhou, Jiangxi 341000, China [2] Beijing Computational Science Research Center, Beijing 100084, China.
authors.forename: Xing
authors.initials: X
authors.lastname: Xiao
authors.affiliation: Beijing Computational Science Research Center, Beijing 100084, China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Yao
authors.affiliation: 1] Beijing Computational Science Research Center, Beijing 100084, China [2] Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Lei-Ming
authors.initials: LM
authors.lastname: Zhou
authors.affiliation: 1] Zhejiang Institute of Modern Physics, Department of Physics, Zhejiang University, Hangzhou, Zhejiang 310027, China [2] Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Xiaoguang
authors.initials: X
authors.lastname: Wang
mesh_terms: D000465:Algorithms; D008962:Models, Theoretical