Quantifying the quantumness of ensembles via unitary similarity invariant norms
Xian-Fei Qi1, Ting Gao1(), Feng-Li Yan2()
1. College of Mathematics and Information Science, Hebei Normal University, Shijiazhuang 050024, China 2. College of Physics Science and Information Engineering, Hebei Normal University, Shijiazhuang 050024, China
The quantification of the quantumness of a quantum ensemble has theoretical and practical significance in quantum information theory. We propose herein a class of measures of the quantumness of quantum ensembles using the unitary similarity invariant norms of the commutators of the constituent density operators of an ensemble. Rigorous proof shows that they share desirable properties for a measure of quantumness, such as positivity, unitary invariance, concavity under probabilistic union, convexity under state decomposition, decreasing under coarse graining, and increasing under fine graining. Several specific examples illustrate the applications of these measures of quantumness in studying quantum information.
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