Entanglement Transfer via Heisenberg Interaction in a Four-Qubit System

We investigate the entanglement transfer in a four-qubit system and calculate the concurrence between any two qubits in different initial states. We show that both the pure entangled state and mixed entangled state can be transferred. For some special coupling constants and some evolution time, entanglement can be completely transferred from one pair particles to another.

Generation of Bell states via Lyapunov control on a two-qubit system with an anisotropic XY Heisenberg interaction

We demonstrate that an arbitrary Bell state can be achieved in a two qubit anisotropic Heisenberg XY chain via Lyapunov control. During the whole process, we only need to apply an external field along a given direction to a single qubit. This control strategy is effective for all initial states in the four-dimensional Hilbert space where the target state is asymptotically stable. The effects of imperfections on the fidelity for the target state such as Gaussian leakage of local control and localized dephasing of individual spins are also considered.

Pairwise thermal entanglement in a three-qubit Heisenberg XX model with a nonuniform magnetic field and Dzyaloshinski-Moriya interaction

Pairwise thermal entanglement in a three-qubit Heisenberg XX model is investigated when a nonuniform mag- netic field and the Dzyaloshinski-Moriya interaction are included. We find that the nonuniform magnetic field and Dzyaloshinski-Moriya interaction are the more efficient control parameters for the increase of entanglement and critical temperature. For both the nearest neighbour sites and the next nearest neighbour sites, the magnetic field can induce entanglement to a certain extent and the Dzyaloshinski-Moriya interaction can enhance the entanglement to a stable value. The steady value of the nearest neighbour site entanglement C12 is larger than the next nearest neighbour site entanglement C13. An interesting phenomenon is that the entanglement curve of C12 appears a peak value when the Dzyaloshinski-Moriya interaction is considered in a nonuniform magnetic field.

Transferring information through a mixed-five-spin chain channel

We initially introduce one-dimensional mixed-five-spin chain with Ising-XY model which includes mixture of spins-1/2 and spins-1. Here, it is considered that nearest spins（1, 1/2） have Ising-type interaction and nearest spins（1/2, 1/2）have both XY-type and Dzyaloshinskii–Moriya（DM） interactions together. Nearest spins（1, 1） have X X Heisenberg interaction. This system is in the vicinity of an external homogeneous magnetic field B in thermal equilibrium state. We promote the quantum information transmitting protocol verified for a normal spin chain with simple model（refer to Rossini D, Giovannetti V and Fazio R 2007 Int. J. Quantum Infor. 5 439）（widely in reference： Giovannetti V and Fazio R 2005 Phys. Rev. A 71 032314） by means of considering the suggested mixed-five-spin chain as a quantum communication channel for transmitting both qubits and qutrits ideally. Hence, we investigate some useful quantities such as quantum capacity and quantum information transmission rate for the system. Finally, we conclude that, when the DM interaction between spins（1/2, 1/2） increases the system is a more ideal channel for transmitting information.

Thermal Quantum Discord in Pure Dzyaloshinskii–Moriya Model with Magnetic Field

We investigate the effects of the directions of Dzyaloshinskii–Moriya(DM) interaction vector and magnetic field on the quantum discord in the pure DM model. For different directions of DM vector, we find that there are different optimal parameter components of magnetic field. Moreover, we find that the optimal parameter components rules are the same for the Hamiltonian H_1 and H_2. According to the rules, for a certain axial DM vector, we can get the maximal quantum discord by adjusting the direction of the external magnetic field, which is feasible under the current experimental technology.