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1.
Thermal entanglement of a two-qutrit Ising system in the presence of an external homogeneous magnetic field and Dzialoshinski-Moriya (DM) interaction is investigated. Influences of magnetic field, temperature, and DM interaction on the entanglement have been characterized in terms of negativity for a wide range of parameters. The cases of parallel, antiparallel and transverse magnetic fields are considered. Results of detailed numerical calculations are explained using the analytically determined ground and excited states of the system. It is shown that at a given temperature, control of entanglement can be optimized by utilizing competing effects of the magnetic field and the DM interaction. 相似文献
2.
The thermal entanglement in a two-spin-qutrit system with two spins coupled by exchange interaction is investigated in terms of the measure of entanglement called ‘negativity’. We strictly show that for any temperature the entanglement is symmetric with respect to zero magnetic field. The behavior of negativity is presented for four different cases. We find that the entanglement may be enhanced under a nonuniform magnetic field. Because there is not any necessary and sufficient condition for quantum separability in systems of dimension 3⊗3, our results are qualitative, not quantitative. 相似文献
3.
Da-Chuang Li 《Optics Communications》2009,282(6):1226-1636
Thermal entanglement is investigated in a two-qubit Heisenberg XYZ system with different inhomogeneous magnetic fields. It is found that different magnetic fields have different entanglement and critical values. In addition, according to the relation of spin-spin coupling coefficients, a more efficient control parameter of magnetic field can be obtained by adjusting the direction of external magnetic field. 相似文献
4.
Taking into account the intrinsic decoherence, the concurrence of the nearest and the next-to-nearest neighbor qubits in a three-qubit Heisenberg XY chain are investigated when a nonuniform magnetic field is included. We show that the effects of the external magnetic field, including the uniform and inhomogeneous magnetic fields, on the time evolution of entanglement between the nearest and the next-to-nearest neighbor qubits rely deeply on the initial states. We can moderate the destructive effect of intrinsic decoherence by controlling the uniform and inhomogeneous magnetic fields, so that a proper value of uniform and inhomogeneous magnetic fields can, to a great extent enhance the stationary entanglement. 相似文献
5.
By using the concept of concurrence, we numerically investigate the thermal entanglement between any two nearest-neighbour spins in uniform and periodic anisotropic XY chains in a transverse field at finite temperature T. It is found that the entanglement has more than one critical temperatures on some parameter regions for uniform and periodic chains. We also discuss the behaviour of the thermal entanglement at the vicinity of quantum phase transition of periodic anisotropic XY chains and find that a11 the derivatives aλC have similar behaviour as that of the uniform chain. 相似文献
6.
Thermal entanglement of the two-qubit XXZ model under magnetic fields in arbitrary directions is studied. Both the uniform and nonuniform fields are addressed. For the ferromagnetic case, a magnetic field perpendicular to the z-axis helps to enhance the entanglement or slows down the decrease of the entanglement. For the antiferromagnetic case, there is the revival phenomenon when the magnetic field is uniform and no such phenomenon when the field is uniform in the z-direction and a staggered type in the x-axis. 相似文献
7.
We propose two schemes to produce long-distance entanglement in a spin chain. The first is based on a controllable interaction system, one starts from an entangled kernel and adds weaken interaction spins to the boundary sites step by step, then the entanglement will be extended longer and longer and its value is equal to that of its kernel. The second is based on a uniform interaction (J) system with a bulk magnetic field (B) that is absent for the boundary qubits, as long as B/J 〉 5, one can obtain near perfect long distance entanglement. Ultra-low temperature is needed in both schemes. 相似文献
8.
Pairwise thermal entanglement of an XXZ ferromagnetic chain with a uniform magnetic field is investigated by using the entanglement measure of negativity. The effects of spin, number of sites, anisotropic parameter, and magnetic field on the threshold temperature are discussed respectively. 相似文献
9.
The SWAP operation in a two-qubit Heisenberg model in the presence of Dzyaloshinskii–Moriya (DM) anisotropic antisymmetric interaction is investigated. It is shown that the SWAP operation can be implemented for some kinds of DM coupling and the influence of DM couplings is divided into different cases. The conditions of the DM coupling under which the SWAP operation is feasible are established. 相似文献
10.
Thermal Entanglement in the Anisotropic Heisenberg XYZ Model with Different Dzyaloshinskii-Moriya Couplings
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Thermal entanglement is investigated in a two-qubit Heisenberg XYZ system with different Dzyaloshinskii Moriya (DM) couplings. It is shown that different DM interaction parameters have different influences on the entanglement and the critical temperature. In addition, according to the relation between the real coupling coefficients Jx and Jz, a more efficient DM control parameter can be obtained by adjusting the direction of DM interaction. 相似文献
11.
We studied the effects of Dzyaloshinski-Moriya (DM) anisoyropic antisymmetric interaction on entanglement and teleportation in a two-qubit Heisenberg chain with intrinsic decoherence taken into account. The main result is the systematic analysis of the negativity and fully entangled fraction’s evolution as a function of DM interaction D and time t. The contrast between the case of the maximally entangled initial state and unentangled ones is presented. 相似文献
12.
We study the effect of the Dzyaloshinskill-Moriya anisotropic antisymmetric interaction (DM interaction) on entanglement teleportation in a two-qubit Heisenberg model with intrinsic decoherence taken into account. For some initial states of the channel, the DM interaction and intrinsic decoherence have no effect on the teleported entanglement and fidelity. While for other one, the DM interaction and intrinsic decoherence have a pronounced effect. 相似文献
13.
The thermodynamics of the unitary (normalized spin) quantum and classical Ising models with skew magnetic field, for |J|β?0.9, is derived for the ferromagnetic and antiferromagnetic cases. The high-temperature expansion (β-expansion) of the Helmholtz free energy is calculated up to order β7 for the quantum version (spin S≥1/2) and up to order β19 for the classical version. In contrast to the S=1/2 case, the thermodynamics of the transverse Ising and that of the XY model for S>1/2 are not equivalent. Moreover, the critical line of the T=0 classical antiferromagnetic Ising model with skew magnetic field is absent from this classical model, at least in the temperature range of |J|β?0.9. 相似文献
14.
Zafer Gedik 《Solid State Communications》2006,138(2):82-85
We study an analytically solvable model for decoherence of a two spin system embedded in a large spin environment. As a measure of entanglement, we evaluate the concurrence for the Bell states (Einstein-Podolsky-Rosen pairs). We find that while for two separate spin baths all four Bell states lose their coherence with the same time dependence, for a common spin bath, two of the states decay faster than the others. We explain this difference by the relative orientation of the individual spins in the pair. We also examine how the Bell inequality is violated in the coherent regime. Both for one bath and two bath cases, we find that while two of the Bell states always obey the inequality, the other two violate the inequality at early times. 相似文献
15.
We investigate the entanglement dynamics and decoherence of a three-qubit system under a quantum spin environment at a finite temperature in the thermodynamics limit. For the case under study, we find the evolution of pairwise entanglement depends not only on the initial states but also on the parameters related to the system and the spin environment. In addition, an undesirable entanglement sudden death occurs in the process of entanglement evolution, and this effect can be controlled by the coupling constant between two qubits, external magnetic field, and the interaction between the system and the environment. 相似文献
16.
G. Lagmago Kamta A. Y. Istomin A. F. Starace 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(2):389-400
We study systematically the entanglement of a two-qubit
Heisenberg XY model in thermal equilibrium in the presence of an
external arbitrarily-directed static magnetic field, thereby
generalizing our prior work [G. Lagmago Kamta, A.F. Starace, Phys.
Rev. Lett. 88, 107901 (2002)]. We show that a magnetic field
having a component in the xy-plane containing the spin-spin
interaction components produces different entanglement for
ferromagnetic (FM) and antiferromagnetic (AFM) couplings. In
particular, quantum phase transitions induced by the magnetic
field-driven level crossings always occur for the AFM-coupled
qubits, but only occur in FM-coupled qubits when the coupling is of
Ising type or when the magnetic field has a component perpendicular
to the xy-plane. When the magnetic field has a component in the
xy-plane, the cut-off temperature above which the entanglement of
both the FM- and AFM-coupled qubits vanishes can always be
controlled using the magnetic field for any value of the XY coupling
anisotropy parameter. Thus, by adjusting the magnetic field, an
entangled state of two spins can be produced at any finite
temperature. Finally, we find that a higher level of entanglement is
achieved when the in-plane component of the magnetic field is
parallel to the direction in which the XY exchange coupling is
smaller. 相似文献
17.
Paula I. Villar 《Physics letters. A》2009,373(2):206-209
We calculate the geometric phase of a spin-1/2 particle coupled to an external environment comprising N spin-1/2 particle in the framework of open quantum systems. We analyze the decoherence factor and the deviation of the geometric phase under a nonunitary evolution from the one gained under an unitary one. We show the dependence upon the system's and bath's parameter and analyze the range of validity of the perturbative approximation. Finally, we discuss the implications of our results. 相似文献
18.
Xiao San Ma 《Optics Communications》2008,281(3):484-488
The effect of Dzialoshinski-Moriya (DM) interaction on thermal entanglement of a two-qutrit XX spin chain in a homogenous magnetic field is investigated. Our results imply that DM interaction and the magnetic field play competing roles in enhancing thermal entanglement. 相似文献
19.
The pairwise entanglement between neighboring spins in a general mixed-spin chain with arbitrary spins S and 1/2 is investigated in the thermodynamical limit. The entanglement is witnessed by the magnetic susceptibility which determines a characteristic temperature for an entangled thermal state. The characteristic temperature is nearly proportional to the interaction J and the mixed-spin S. The bound of negativity is obtained on the basis of the magnetic susceptibility. It is found that the macroscopic magnetic properties are affected by the quantum entanglement in the real solids. 相似文献
20.
A scheme is proposed to deterministically create maximal entanglement between hybrid artificial atoms: superconducting charge and flux qubits. By tuning the circuit, the two qubits are dynamically decoupled and entanglement can be long-lived. This provides a new version of the Einstein-Podolsdy-Rosen (EPR) situation where the components of a macroscopic EPR pair are in opposite regimes. 相似文献