Comment on ``Optimal convex approximations of quantum states"
Xiao-Bin Liang, Bo Li, and Shao-Ming Fei
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Submission date: 11. Feb. 2019
published in: Physical review / A, 99 (2019) 1, art-no. 016301
DOI number (of the published article): 10.1103/PhysRevA.99.016301
with the following different title: Comment on ''Optimal convex approximations of quantum states'' [Phys. Rev. A 96, 042325 (2017)]
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In a recent paper, Massimiliano F. Sacchi [Phys. Rev. A 96, 042325 (2017)] addressed the general problem of approximating an unavailable quantum state by the convex mixing of different available states. For the case of qubit mixed states, we show that the analytical solutions in some cases are invalid. In this comment, we present the complete analytical solutions for the optimal convex approximation. Our solutions can be viewed as the supplement to the results in [Phy. Rev. A 96, 042325(2017)]