tailieunhanh - Báo cáo toán học: "The tripartite separability of density matrices of graphs"

Tuyển tập các báo cáo nghiên cứu khoa học về toán học trên tạp chí toán học quốc tế đề tài: The tripartite separability of density matrices of graphs. | The tripartite separability of density matrices of graphs Zhen Wang and Zhixi Wang Department of Mathematics Capital Normal University Beijing 100037 China wangzhen061213@ wangzhx@ Submitted May 9 2007 Accepted May 16 2007 Published May 23 2007 Mathematics Subject Classification 81P15 Abstract The density matrix of a graph is the combinatorial laplacian matrix of a graph normalized to have unit trace. In this paper we generalize the entanglement properties of mixed density matrices from combinatorial laplacian matrices of graphs discussed in Braunstein et al. Annals of Combinatorics 10 2006 291 to tripartite states. Then we prove that the degree condition defined in Braunstein et al. Phys. Rev. A 73 2006 012320 is sufficient and necessary for the tripartite separability of the density matrix of a nearest point graph. 1 Introduction Quantum entanglement is one of the most striking features of the quantum formalism 1 . Moreover quantum entangled states may be used as basic resources in quantum information processing and communication such as quantum cryptography 2 quantum parallelism 3 quantum dense coding 4 5 and quantum teleportation 6 . So testing whether a given state of a composite quantum system is separable or entangled is in general very important. Recently normalized laplacian matrices of graphs considered as density matrices have been studied in quantum mechanics. One can recall the definition of density matrices of graphs from 8 . Ali Saif M. Hassan and Pramod Joag 9 studied the related issues like classification of pure and mixed states von Neumann entropy separability of multipartite quantum states and quantum operations in terms of the graphs associated with quantum states. Chai Wah Wu 10 showed that the Peres-Horodecki positive partial transpose condition is necessary and sufficient for separability in C2 Cq. Braunstein et al. 11 proved that the degree condition is necessary for separability of density matrices of any graph and .

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