Xiao San Ma

Entanglement sudden death in a spin channel

We study the dynamic evolution of the entanglement in a spin channel with an XY-type interaction initially in an entangled state. We find that the phenomenon of entanglement sudden death (ESD) appears in the evolution of entanglement for some initial states. We calculate the entanglement and obtain the parameter regions of disentanglement for the chains with several numbers of sites. The influence of the presence of one common spin environment is also discussed.

Entanglement dynamics and decoherence of three-qubit system in a fermionic environment

We study the entanglement dynamics of the three-qubit system in a symmetry-broken environment consisting of a fermionic bath. Decoherence induced by the bath is analysed. We find that the entanglement of states will decrease or remain unchanged under the system–bath interaction. The class of decoherence-free states of the three-qubit system of our model has been found out.

Tripartite entanglement of a spin star model with Dzialoshinski---Moriya interaction

The effect of Dzialoshinski–Moriya (DM) interaction on the tripartite thermal entanglement of a spin-star model with four spins has been analyzed by an entanglement measure of the tripartite negativity. Our results imply that the tripartite thermal entanglement can be established among the three surrounding parties which do not interact with each other but interact with the central party independently. From the results, we find that the strong DM interaction can enhance the tripartite thermal entanglement while the high temperature can shrink it. The effect of the inhomogeneous coupling on the tripartite thermal entanglement is also discussed.

QUANTUM DISCORD IN THE THERMAL STATES OF A SPIN-STAR SYSTEM

We investigate the quantum discord in the thermal states for a spin-star model consisting of three parties which include one central spin and the other two outer spins. Our results imply that the quantum correlation can be established between the two outer spins both of which interacting with the central spin independently. From the analysis, we find that the quantum discord and entanglement depends not only on the external magnetic field and the interaction strength but also on the anisotropy parameter and the temperature. Specially, the quantum discord is more robust than the quantum entanglement in the sense that the quantum discord lasts for higher temperatures than the entanglement does.

Three-qubit entanglement generation of quantum states dissipating into a common environment

In this paper, we investigate the dynamics of entanglement of three-qubit states of a system dissipating into a common environment. By using the tripartite negativity as entanglement measure, our results imply that the three-qubit entanglement can be generated among the three qubits which have no interaction with each other, but interact with the common environment independently. From our analysis, we find that the three-qubit entanglement increases from zero to a stable value which varies with the size of the system with the increasing of the scaled time. Additionally, the extension of the entanglement generation to an arbitrary size of a subsystem is made and some discussion is given.

Tripartite entanglement of electron spins of noninteracting electron gases

By using the tripartite negativity as entanglement measure, we study the tripartite entanglement of electron spins of noninteracting electron gases. Our results imply that the tripartite entanglement depends on the relative distance between the three spins and the temperature. By a comparison between the tripartite negativity and quantum mutual information, for the symmetrical configuration that the relative distances between each pair of the three spins are the same, the quantum mutual information lasts a longer relative distance than the tripartite negativity does. While for the unsymmetrical configuration, the analysis imply that the tripartite negativity just measures the tripartite correlation while the quantum mutual information maybe takes the bipartite correlation into account.

Effect of Dzyaloshinskii–Moriya anisotropic antisymmetric interaction on optimal dense coding

We study optimal dense coding in the two-qubit and two-qutrit Heisenberg XXX models with Dzyaloshinskii–Moriya anisotropic antisymmetric interaction (DM interaction). Both the DM interaction and the coupling parameter can enhance the maximum dense coding capacity for high temperature. For low temperature, in the two-qutrit system, the coupling parameter still enhances the maximum dense coding capacity, while the DM interaction weakens the capacity of the channel for dense coding.