The norms of Bloch vectors and classification of four qudits quantum states

Ming Li, Zong Wang, Jing Wang, Shu-Qian Shen, and Shao-Ming Fei

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Submission date: 11. Feb. 2019
Pages: 15
published in: epl, 125 (2019) 2, art-no. 20006 
DOI number (of the published article): 10.1209/0295-5075/125/20006
Bibtex
with the following different title: The norms of Bloch vectors and classification of four-qudits quantum states
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Abstract:
We investigate the norms of the Bloch vectors for any quantum state with subsystems less than or equal to four. Tight upper bounds of the norms are obtained, which can be used to derive tight upper bounds for entanglement measure defined by the norms of Bloch vectors. By using these bounds a trade-off relation of the norms of Bloch vectors is discussed. Theses upper bounds are then applied on separability. Necessary conditions are presented for different kinds of separable states in four-partite quantum systems. We further present a complete classification of quantum states for four qudits quantum systems.