Tian Li-Jun

Quantum Correlation in Three-Qubit Heisenberg Model with Dzyaloshinskii—Moriya Interaction

We investigate the pairwise thermal quantum discord in a three-qubit XXZ model with Dzyaloshinskii-Moriya (DM) interaction. We find that the effects of DM interaction on antiferromagnetic system is distinct from that of ferromagnetic system. The magnetic field supplemented with DM term contribute to enhance the range of quantum discord. It is revealed that the situations where quantum discord fails to indicate a sudden change of groundstate at finite temperature though indicating such a sudden change of groundstate at zero temperature. Dynamics of pairwise thermal quantum discord is considered as well. Thermal quantum discord vanishes in asymptotic limit regardless of its initial values, however, thermal entanglement suddenly disappears in finite time.We investigate the pairwise thermal quantum discord in a three-qubit XXZ model with Dzyaloshinskii—Moriya (DM) interaction. We find that the effects of DM interaction on antiferromagnetic system is distinct from that of ferromagnetic system. The magnetic field supplemented with DM term contribute to enhance the range of quantum discord. It is revealed that the situations where quantum discord fails to indicate a sudden change of groundstate at finite temperature though indicating such a sudden change of groundstate at zero temperature. Dynamics of pairwise thermal quantum discord is considered as well. Thermal quantum discord vanishes in asymptotic limit regardless of its initial values, however, thermal entanglement suddenly disappears in finite time.

Sudden Transition in Quantum Discord Dynamics: Role of Three-Site Interaction

We investigate the dynamics of quantum discord for a two-qubit system coupled to a spin chain with three-site interaction in the weak-coupling region. For the case of the initial two-qubit pure state, the decay of quantum discord can be delayed in a special interval of the three-site coupling strength. In the absence of the transverse field, with the increase of three-site interaction, quantum discord tends to be stabler. For the case of the initial mixed state, the increase of quantum discord is delayed in the special interval of three-site interaction. In addition, a sudden transition between classical and quantum decoherence is also observed, with the transition time determined by the three-site interaction and degree of anisotropy.

Fidelity Susceptibility in the SU(2) and SU(1,1) Algebraic Structure Models

We mainly explore the fidelity susceptibility based on the Lie algebraic method. On physical grounds, the exact expressions of fidelity susceptibilities can be respectively obtained in SU(2) and SU(1,1) algebraic structure models, which are applied to one-body system and many-body systems, such as the single spin model, the single-mode squeeze harmonic oscillator model and the BCS model. In terms of the double-time Green-function method, our general conclusions are illustrated with two models which exhibit the fidelity susceptibilities at the finite temperature and T = 0.

Stability of Disclinations in Nematic Liquid Crystals

In the light of -mapping method and topological current theory, the stability of disclinations around a spherical particle in nematic liquid crystals is studied. We consider two different defect structures around a spherical particle: disclination ring and point defect at the north or south pole of the particle. We calculate the free energy of these different defects in the elastic theory. It is pointed out that the total Frank free energy density can be divided into two parts. One is the distorted energy density of director field around the disclinations. The other is the free energy density of disclinations themselves, which is shown to be concentrated at the defect and to be topologically quantized in the unit of (k−k24)π/2. It is shown that in the presence of saddle-splay elasticity a dipole (radial and hyperbolic hedgehog) configuration that accompanies a particle with strong homeotropic anchoring takes the structure of a small disclination ring, not a point defect.

Two-Qubit Quantum Logic Gate in Molecular Magnets

We proposed a scheme to realize a controlled-NOT quantum logic gate in a dimer of exchange coupled single-molecule magnets,

Non-Markovianity of a qubit coupled with an isotropic Lipkin–Meshkov–Glick bath*

[\textrm{Mn}_4]_2

Non-Markovianity of the Heisenberg XY spin environment with Dzyaloshinskii—Moriya interaction

. We chosen the ground state and the three low-lying excited states of a dimer in a finite longitudinal magnetic field as the quantum computing bases and introduced a pulsed transverse magnetic field with a special frequency. The pulsed transverse magnetic field induces the transitions between the quantum computing bases so as to realize a controlled-NOT quantum logic gate. The transition rates between the quantum computing bases and between the quantum computing bases and other excited states are evaluated and analyzed.We propose a scheme to realize a controlled-NOT quantum logic gate in a dimer of exchange coupled single-molecule magnets, [Mn4]2. We chosen the ground state and the three low-lying excited states of a dimer in a finite longitudinal magnetic field as the quantum computing bases and introduced a pulsed transverse magnetic field with a special frequency. The pulsed transverse magnetic field induces the transitions between the quantum computing bases so as to realize a controlled-NOT quantum logic gate. The transition rates between a pair of the four quantum computing bases and between the quantum computing bases and excited states are evaluated and analysed.

Entanglement of Two-Superconducting-Qubit System Coupled with a Fixed Capacitor

We study the non-Markovianity of the single qubit system coupled with an isotropic Lipkin–Meshkov–Glick (LMG) model by an effective method proposed by Breuer et al. (Breuer H P and Piilo J 2009 Europhys. Lett. 85 5004). It is discovered that the non-Markovianity is concerned with the quantum phase transitions (QPTs). In the open system, we present that the strong coupling inside the bath and the strong interaction between the system and bath can enhance the degree of non-Markovianity. Moreover, the non-Markovianity is stronger and more sensitive for the bath in the symmetric phase than the symmetry broken phase.

Fidelity susceptibility and geometric phase in critical phenomenon

Using the effective non-Markovian measure proposed by Breuer et al. recently, we study the memory effect of a central qubit system coupled to a spin chain environment with Dzyaloshinskii—Moriya interaction in a transverse field. It is discovered that the central qubit system presents different memory effects in different environment phases with the different oscillatory behaviors of the decoherence factor. Moreover, it is revealed that the Dzyaloshinskii—Moriya interaction has a prominent influence on the memory effect of a central qubit system via modifying the amplitude and period of the decoherence factor under certain conditions.

Reduced Properties and Applications of Y(sl(2)) Algebra for a Two-Spin System

We study thermal entanglement in a two-superconducting-qubit system in two cases, either identical or distinct. By calculating the concurrence of system, we find that the entangled degree of the system is greatly enhanced in the case of very low temperature and Josephson energies for the identical superconducting qubits and our result is in a good agreement with the experimental data.