4,233 research outputs found
Concurrence of arbitrary dimensional bipartite quantum states
We derive an analytical lower bound for the concurrence of a bipartite
quantum state in arbitrary dimension. A functional relation is established
relating concurrence, the Peres-Horodecki criterion and the realignment
criterion. We demonstrate that our bound is exact for some mixed quantum
states. The significance of our method is illustrated by giving a quantitative
evaluation of entanglement for many bound entangled states, some of which fail
to be identified by the usual concurrence estimation method.Comment: 4 pages, published versio
Entanglement of Formation of Bipartite Quantum States
We give an explicit tight lower bound for the entanglement of formation for
arbitrary bipartite mixed states by using the convex hull construction of a
certain function. This is achieved by revealing a novel connection among the
entanglement of formation, the well-known Peres-Horodecki and realignment
criteria. The bound gives a quite simple and efficiently computable way to
evaluate quantitatively the degree of entanglement for any bipartite quantum
state.Comment: 4 page
Stabilization and current-induced motion of antiskyrmion in the presence of anisotropic Dzyaloshinskii-Moriya interaction
Topological defects in magnetism have attracted great attention due to
fundamental research interests and potential novel spintronics applications.
Rich examples of topological defects can be found in nanoscale non-uniform spin
textures, such as monopoles, domain walls, vortices, and skyrmions. Recently,
skyrmions stabilized by the Dzyaloshinskii-Moriya interaction have been studied
extensively. However, the stabilization of antiskyrmions is less
straightforward. Here, using numerical simulations we demonstrate that
antiskyrmions can be a stable spin configuration in the presence of anisotropic
Dzyaloshinskii-Moriya interaction. We find current-driven antiskyrmion motion
that has a transverse component, namely antiskyrmion Hall effect. The
antiskyrmion gyroconstant is opposite to that for skyrmion, which allows the
current-driven propagation of coupled skyrmion-antiskyrmion pairs without
apparent skyrmion Hall effect. The antiskyrmion Hall angle strongly depends on
the current direction, and a zero antiskyrmion Hall angle can be achieved at a
critic current direction. These results open up possibilities to tailor the
spin topology in nanoscale magnetism, which may be useful in the emerging field
of skyrmionics.Comment: 31 pages, 6 figures, to appear in Physical Review
Study the Heavy Molecular States in Quark Model with Meson Exchange Interaction
Some charmonium-like resonances such as X(3872) can be interpreted as
possible molecular states. Within the quark model, we study
the structure of such molecular states and the similar
molecular states by taking into account of the light meson exchange (,
, , and ) between two light quarks from different
mesons
Entanglement in SO(3)-invariant bipartite quantum systems
The structure of the state spaces of bipartite (N tensor N) quantum systems
which are invariant under product representations of the group SO(3) of
three-dimensional proper rotations is analyzed. The subsystems represent
particles of arbitrary spin j which transform according to an irreducible
representation of the rotation group. A positive map theta is introduced which
describes the time reversal symmetry of the local states and which is unitarily
equivalent to the transposition of matrices. It is shown that the partial time
reversal transformation theta_2 = (I tensor theta) acting on the composite
system can be expressed in terms of the invariant 6-j symbols introduced by
Wigner into the quantum theory of angular momentum. This fact enables a
complete geometrical construction of the manifold of states with positive
partial transposition and of the sets of separable and entangled states of (4
tensor 4) systems. The separable states are shown to form a three-dimensional
prism and a three-dimensional manifold of bound entangled states is identified.
A positive maps is obtained which yields, together with the time reversal, a
necessary and sufficient condition for the separability of states of (4 tensor
4) systems. The relations to the reduction criterion and to the recently
proposed cross norm criterion for separability are discussed.Comment: 15 pages, 3 figure
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