Four-qubit entanglement has been investigated using a recent proposed entanglement measure, multiple entropy measures （MEMS）. We have performed optimization for the nine different families of states of four-qubit sy...Four-qubit entanglement has been investigated using a recent proposed entanglement measure, multiple entropy measures （MEMS）. We have performed optimization for the nine different families of states of four-qubit system. Some extremal entangled states have been found.展开更多
Paolo Facchi,et al.[Phys.Rev.A 77 (2008)060304(R)]presented a maximally multipartite entangledstate (MMES).Here,we give a criterion for the identification of maximally entangled four-qubit states.Using thiscriterion,w...Paolo Facchi,et al.[Phys.Rev.A 77 (2008)060304(R)]presented a maximally multipartite entangledstate (MMES).Here,we give a criterion for the identification of maximally entangled four-qubit states.Using thiscriterion,we not only identify some existing maximally entangled four-qubit states in the literature,but also find severalnew maximally entangled four-qubit states as well.展开更多
In order to improve the eavesdropping detection efficiency in a two-step quantum direct communication protocol, an improved eavesdropping detection strategy using the four-particle cluster state is proposed, in which ...In order to improve the eavesdropping detection efficiency in a two-step quantum direct communication protocol, an improved eavesdropping detection strategy using the four-particle cluster state is proposed, in which the four-particle cluster state is used to detect eavesdroppers. During the security analysis, the method of the entropy theory is introduced, and two detection strategies are compared quantitatively using the constraint between the information that the eavesdropper can obtain and the interference that has been introduced. If the eavesdroppers intend to obtain all information, the eavesdropping detection rate of the original two-step quantum direct communication protocol using EPR pair block as detection particles will be 50%; while the proposed strategy's detection rate will be 75%. In the end, the security of the proposed protocol is discussed. The analysis results show that the eavesdropping detection strategy presented is more secure.展开更多
基金National Natural Science Foundation of China under Grant Nos.10325521 and 60433050the 973 Program under Grant No.2006CB921106
文摘Four-qubit entanglement has been investigated using a recent proposed entanglement measure, multiple entropy measures （MEMS）. We have performed optimization for the nine different families of states of four-qubit system. Some extremal entangled states have been found.
基金Supported by the National Natural Science Foundation of China under Grant No. 10902083Shaanxi Natural Science Foundation under Grant No. 2009JM1007
文摘Paolo Facchi,et al.[Phys.Rev.A 77 (2008)060304(R)]presented a maximally multipartite entangledstate (MMES).Here,we give a criterion for the identification of maximally entangled four-qubit states.Using thiscriterion,we not only identify some existing maximally entangled four-qubit states in the literature,but also find severalnew maximally entangled four-qubit states as well.
基金supported by the National Natural Science Foundation of China (61100205)
文摘In order to improve the eavesdropping detection efficiency in a two-step quantum direct communication protocol, an improved eavesdropping detection strategy using the four-particle cluster state is proposed, in which the four-particle cluster state is used to detect eavesdroppers. During the security analysis, the method of the entropy theory is introduced, and two detection strategies are compared quantitatively using the constraint between the information that the eavesdropper can obtain and the interference that has been introduced. If the eavesdroppers intend to obtain all information, the eavesdropping detection rate of the original two-step quantum direct communication protocol using EPR pair block as detection particles will be 50%; while the proposed strategy's detection rate will be 75%. In the end, the security of the proposed protocol is discussed. The analysis results show that the eavesdropping detection strategy presented is more secure.
基金Supported by the Talent Foundation of High Education of Anhui Province for Outstanding Youth under Grant(2009SQRZ056)Young Teachers Fund of Anhui University of Science and Technology tinder Grant(2012QNZ13)Master,Doctorate Fund of Anhui University of Science and Technology under Grant(200911176)
