Quantum displacements

In this paper, first we explain what are the `quantum displacements'. We establish a group of bases, which contains the coupled bases coupling a ququart and a bipartite qubit systems. By these bases, we can realize the quantum displacements. We discuss some possible forms of them. At last, we point out that a so-call ''non-imprecisely-cloning theorem'' also holds.Comment: 11 pages, no figures, revisio

Special reduction of density matrixes and entanglement between two bunches of particles

By using of a special reduction way of density matrices, in this Letter we find the entanglement between two bunches of particles, its measure can be represented by the entanglement of formation.Comment: REVTeX, 5 pages, no figur

Criteria of partial separability of multipartite qubit mixed-states

In this paper, we discuss the partial separability and its criteria problems of multipartite qubit mixed-states. First we strictly define what is the partial separability of a multipartite qubit system. Next we give a reduction way from N-partite qubit density matrixes to bipartite qubit density matrixes, and prove a necessary condition that a N-partite qubit mixed-state to be partially separable is its reduction to satisfy the PPT condition. PACC numbers: 03.67.Mn; 03.65.Ud; 03.67.HkComment: 13 pages, no figure, the revision of quant-ph/040317

Return operator, cross Bell bases and protocol of teleportation of arbitrary multipartite qubit entanglement

In this paper, we define the return operator, the cross product operator and the cross Bell bases. Using the cross Bell bases, we give a protocol of teleportation of arbitrary multipartite qubit entanglement, this scheme is a quite natural generalization of the BBCJPW scheme. We find that this teleportation, in fact, is essentially determined by the teleportation of every single unknown qubit state as in the original scheme of BBCJPW. The calculation in detail is given for the case of tripartite qubit.Comment: 5 pages, no figur

Reduction of multipartite qubit density matrixes to bipartite qubit density matrixes and criteria of partial separability of multipartite qubit density matrixes

The partial separability of multipartite qubit density matrixes is strictly defined. We give a reduction way from N-partite qubit density matrixes to bipartite qubit density matrixes, and prove a necessary condition that a N-partite qubit density matrix to be partially separable is its reduced density matrix to satisfy PPT condition.Comment: 5 pages, no figur

Sufficient conditions of entanglement for tripartite and higher dimensional multipartite qubit density matrixes

In this paper we give the new sufficient conditions of entanglement for multipartite qubit density matrixes. We discuss in detail the case for tripartite qubit density matrixes. As a criterion in concrete application, its steps are quite simple and easy to operate. Some examples and discussions are given. PACC numbers: 03.67.Mn, 03.65.Ud, 03.67.Hk.Comment: REVTex, 5 pages, no figur

Four-level quantum teleportation, swapping and collective translations of multipartite quantum entanglement

In this paper, an optimal scheme of four-level quantum teleportation and swapping of quantum entanglement is given. We construct a complete orthogonal basis of the bipartite ququadrit systems. Using this basis, the four-level quantum teleportation and swapping can be achieved according to the standard steps. In addition, associate the above bases with the unextendible product bases and the exact entanglement bases, we prove that in the $2\times 2\times 2$ systems or $3\times 3$ systems the collective translations of multipartite quantum entanglement can be realized. PACC numbers: 03.67.Mn, 03.65.Ud, 03.67.Hk. Keywords: Ququadrit systems, Bases, Four-level teleportation, Swapping, Collective translations.Comment: 9 pages, no figures, revised versio

Convex rigid cover method in studies of quantum pure-states of many continuous variables

In this paper we prove that every pure-state $\Psi ^{(N)}$ of N (N$\geqslant 3)$ continuous variables corresponds to a pair of convex rigid covers (CRCs) structures in the continuous-dimensional Hilbert-Schmidt space. Next we strictly define what are the partial separability and ordinary separability, and discuss how to use CRCs to describe various separability. We discuss the problem of the classification of $\Psi ^{(N)}$ and give a kinematical explanation of the local unitary operations acting upon $\Psi ^{(N)}$. Thirdly, we discuss the invariants of classes and give a possible physical explanation.Comment: 5 pages, no figure

New criteria of separability for tripartite and more high dimensional multipartite qubit density matrixes

In this Letter we find the new criteria of separability of multipartite qubit density matrixes. Especially, we discuss in detail the criteria of separability for tripartite qubit density matrixes. We find the sufficient and necessary conditions of separability for tripartite qubit density matrixes, and give two corollaries. The second corollary can be taken as the criterion of existence of entanglement for tripartite qubit density matrixes. In concrete application, its steps are quite simple and easy to operate. Some examples, discussions and the generalization to more high dimensional multipartite qubit density matrixes are given.Comment: REVTex, 5 pages, no figur

A simple scheme of teleportation of arbitrary multipartite qubit entanglement

In this paper, we define a cross product operator and construct the cross Bell basis, by use this basis and Bell measurements we give a simple scheme of the teleportation of arbitrary multipartite qubit entanglement.Comment: 3 pages, no figur