Abstract
We describe the structure of all bijective maps on the cone of positive definite operators acting on a finite and at least two-dimensional complex Hilbert space which preserve the quantum \(\chi _\alpha ^2\)-divergence for some \(\alpha \in [0,1]\). We prove that any such transformation is necessarily implemented by either a unitary or an antiunitary operator. Similar results concerning maps on the cone of positive semidefinite operators as well as on the set of all density operators are also derived.
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The reviewer of the paper pointed out that the convexity part of this statement follows also from a celebrated result of Lieb, see Corollary 2.1 in Convex trace functions and the Wigner–Yanase–Dyson conjecture, Advances in Math. 11 (1973), 267–288.
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Acknowledgements
Gy. P. Gehér and L. Molnár were supported by the “Lendület” Program (LP2012-46/2012) of the Hungarian Academy of Sciences and by the National Research, Development and Innovation Office - NKFIH, Grant No. K115383. D. Virosztek was supported by the “Lendület” Program (LP2012-46/2012) of the Hungarian Academy of Sciences, by the National Research, Development and Innovation Office - NKFIH, Grant No. K104206, and by the “For the Young Talents of the Nation” scholarship program (NTP-EFÖ-P-15-0481) of the Hungarian State. The project was also supported by the joint venture of Taiwan and Hungary MOST-HAS, Grant No. 104-2911-1-110-508.
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Chen, HY., Gehér, G.P., Liu, CN. et al. Maps on positive definite operators preserving the quantum \(\chi _\alpha ^2\)-divergence. Lett Math Phys 107, 2267–2290 (2017). https://doi.org/10.1007/s11005-017-0989-0
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DOI: https://doi.org/10.1007/s11005-017-0989-0