Thermal quantum correlations in a two-dimensional spin star model

2019 ◽  
Vol 34 (22) ◽  
pp. 1950175 ◽  
Author(s):  
Saeed Haddadi ◽  
Mohammad Reza Pourkarimi ◽  
Ahmad Akhound ◽  
Mehrdad Ghominejad
Keyword(s):  
Magnetic Field ◽  
Weak Coupling ◽  
Quantum Discord ◽  
Thermal Evolution ◽  
Coupling Parameter ◽  
Quantum Correlations ◽  
Two Dimensional ◽  
Star Model ◽  
Inhomogeneous Spin ◽  
Hamiltonian Parameters

In this paper, we study the thermal evolution of three types of quantum correlations under the homogeneous and inhomogeneous spin star Hamiltonian. It is shown that quantum discord (QD) is more stable than the other measures in the thermal regime, but concurrence is more efficient when the Hamiltonian parameters are employed. However, all quantum correlations can reach their maximum, if the inhomogeneous parameter raises. Quantum correlations can be enhanced by a weak external magnetic field and strong coupling parameter. But they vanish in the case of a strong magnetic field, weak coupling parameter, and high temperatures.

Thermal geometric discords in a two-qutrit system

2016 ◽  
Vol 14 (03) ◽  
pp. 1650016 ◽  
Author(s):  
Ya-Li Yuan ◽  
Xi-Wen Hou
Keyword(s):  
Magnetic Field ◽  
Quantum Information ◽  
Magnetic Fields ◽  
Weak Magnetic Field ◽  
Quantum Discord ◽  
Quantum Information Processing ◽  
Thermal State ◽  
Quantum Correlations ◽  
High Dimensional ◽  
Lower Temperature

The investigation of quantum discord has mostly focused on two-qubit systems due to the complicated minimization involved in quantum discord for high-dimensional states. In this work, three geometric discords are studied for the thermal state in a two-qutrit system with various couplings, external magnetic fields, and temperatures as well, where the entanglement measured in terms of the generalized negativity is calculated for reference. It is shown that three geometric discords are more robust against temperature and magnetic field than the entanglement negativity. However, all four quantities exhibit a similar behavior at lower temperature and weak magnetic field. Remarkably, three geometric discords at finite temperature reveal the phenomenon of double sudden changes at different magnetic fields while the negativity does not. Moreover, the hierarchy among three discords is discussed. Those adjustable discords with the varied coupling, temperature, and magnetic field are useful for the understanding of quantum correlations in high-dimensional states and quantum information processing.

scholarly journals Thermal Quantum Coherence properties in Two-Qubit Heisenberg XXX Model in Nonhomogeneous Magnetic Field

2021 ◽  
Author(s):  
Asad Ali ◽  
Muhammad Anees Khan
Keyword(s):  
Magnetic Field ◽  
Quantum Coherence ◽  
Uniform Magnetic Field ◽  
Coupling Parameter ◽  
Magnetic Interaction ◽  
Threshold Value ◽  
Quantum Correlations ◽  
Qubit System ◽  
Xxx Model ◽  
Heisenberg Xxx Model

We investigate the behavior of thermal quantum coherence in the Heisenberg XXX model for a two-qubit system placed in independently controllable Inhomogeneous magnetic fields applied to two qubits respectively. We discuss the behavior of quantum coherence by systematically varying the coupling parameter, magnetic field, and temperature for both ferromagnetic and antiferromagnetic cases. The results show the interesting behavior of quantum coherence in a certain range of parameters. Generally, it is observed that quantum correlations decay with temperature, but in the ferromagnetic case with uniform magnetic interaction, it rises with temperature up to a certain threshold value and ultimately it decreases its value to zero. Moreover, it is observed that preserving the quantum coherence for small temperatures is very hard with the increasing magnetic field because, at small temperatures, quantum coherence decays sharply with the increase in magnetic field whereas at larger temperatures it decays completely at fairly large values of the magnetic field. The variation of quantum coherence with uniform magnetic field in the antiferromagnetic case is observed to be Gaussian for larger temperature but at zero or nearly zero temperature, it behaves as a constant function for uniform magnetic field up to a threshold value and then decays to zero with an infinite slope. This shows the signature of quantum phase transition from quantum nature to classicality.

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

2011 ◽  
Vol 25 (30) ◽  
pp. 2289-2297 ◽  
Author(s):  
XIAO SAN MA ◽  
GUANG XING ZHAO ◽  
JIA YAN ZHANG ◽  
AN MIN WANG
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Quantum Correlation ◽  
Quantum Discord ◽  
Anisotropy Parameter ◽  
Interaction Strength ◽  
The Other ◽  
Star System ◽  
Star Model ◽  
Thermal States

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.

A two-dimensional analysis of mode conversion at a resonance layer with high-magnetic field side reflection

2007 ◽  
Vol 73 (4) ◽  
pp. 473-484
Author(s):  
NORA NASSIRI-MOFAKHAM ◽  
AKBAR PARVAZIAN
Keyword(s):  
Magnetic Field ◽  
High Magnetic Field ◽  
High Field ◽  
Mode Conversion ◽  
Coupling Parameter ◽  
Local Heating ◽  
Current Drive ◽  
Planar Geometry ◽  
Two Dimensional ◽  
Additional Degree

AbstractMode converted Bernstein waves potentially allow the implementation of local heating and current drive in spherical torus devices, which are not directly accessible to low-harmonic cyclotron waves. The mode conversion method of Cairns and Lashmore-Davies previously used to study the usual mode conversion in non-planar geometry is extended to include the effect of the high-magnetic-field-side cutoff, and is solved analytically. The analytic solutions to the triplet, cutoff–resonance–cutoff, equations give the reflection and conversion coefficients in terms of parameters defining the local behavior of the dispersion relation. The variation of mode conversion efficiency depends not only on the coupling parameter but also on the phasing effect introduced by the high-field-side cutoff. The change in characteristic phases, which are concerned with the coupling parameter, brings an additional degree of freedom allowing optimization via the position of the high-field cutoff. A discrete spectrum of phases exists for which complete mode conversion of the incident wave for a transit of the resonance region can be achieved. The results we obtain here give the general conditions for efficient Bernstein wave heating in two-dimensional geometry.

Kinetic theory of a two-dimensional magnetized plasma. Part 3. Limit of very large magnetic field

1972 ◽  
Vol 8 (3) ◽  
pp. 375-378 ◽  
Author(s):  
George Vahala
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Kinetic Theory ◽  
Conservation Laws ◽  
Weak Coupling ◽  
Plasma Parameter ◽  
Bbgky Hierarchy ◽  
Magnetized Plasma ◽  
Two Dimensional ◽  
Particle Orbits

The BBGKY hierarchy for a two-dimensional magnetized plasma is considered in the weak-coupling and small plasma parameter limits for very large magnetic fields. The Fokker-Planck and Balescu-Lenard equations satisfy an H-theorem and conservation laws, and exhibit two cut-offs related to the periodicity of the particle orbits and to the distance of closest approach of a thermal particle.

CONTINUOUS UPPER BOUND ON THE GROUND-STATE ENERGY OF THE FRÖHLICH POLARON

1994 ◽  
Vol 08 (08n09) ◽  
pp. 553-560 ◽  
Author(s):  
A. V. SOLDATOV
Keyword(s):  
Magnetic Field ◽  
Asymptotic Behavior ◽  
Ground State Energy ◽  
Upper Bound ◽  
Ground State ◽  
Coherent States ◽  
Weak Coupling ◽  
State Energy ◽  
Coupling Parameter ◽  
Weak Coupling Limit

The upper bound on the ground-state energy for the Fröhlich polaron is derived by means of a new version of variational principle based on the Wick symbols formalism and the coherent states theory. The bound is continuous in some respect, i.e. it is valid for all values of coupling parameter including the intermediate regions. Asymptotic behavior of the bound for the weak coupling limit and for the strong coupling limit provides, in general, lower values than well-known existing bounds. The bound can be readily generalized for the case of nonzero magnetic field.

Thermal quantum correlations in a two-qubit Heisenberg XYZ model with different magnetic fields

2015 ◽  
Vol 13 (06) ◽  
pp. 1550046 ◽  
Author(s):  
Zheng Hu ◽  
Yu-Chen Wang ◽  
Xi-Wen Hou
Keyword(s):  
Magnetic Field ◽  
Information Processing ◽  
Quantum Information ◽  
Magnetic Fields ◽  
Finite Temperature ◽  
Quantum Discord ◽  
Quantum Information Processing ◽  
Quantum Correlations ◽  
Field Coupling ◽  
Magnetic Field Coupling

Two kinds of thermal quantum correlations, measured respectively by quantum discord (QD) and the generalized negativity (GN), are studied for various magnetic fields, couplings, and temperatures in a two-qubit Heisenberg XYZ model. It is shown that QD and GN can exhibit a similar behavior in some regions of magnetic field, coupling, and temperature, while they behave in a contrary manner in other regions. For example, QD may increase with suitable magnetic fields, couplings, and temperature when GN decreases. QD is more robust against temperature than GN, and can reveal a kink at a suitable coupling at finite temperature while GN cannot. Moreover, a nearly unchanged QD or GN can be obtained in a large region of magnetic field, coupling, and temperature. These adjustable QD and GN via the varied magnetic field, coupling, and temperature may have significant applications in quantum information processing.

Quantum correlations in Heisenberg XY spin-1 and spin-1/2 model with Dzyaloshinskii–Moriya interactions

2015 ◽  
Vol 13 (05) ◽  
pp. 1550035 ◽  
Author(s):  
Wajid Hussain Joyia
Keyword(s):  
Magnetic Field ◽  
Phase Transition ◽  
Quantum Phase Transition ◽  
Quantum Correlation ◽  
Quantum Discord ◽  
Quantum Correlations ◽  
Spin Systems ◽  
Quantum Phase ◽  
Xy Model ◽  
Higher Spin

We study the quantum correlations in a spin-1/2 (qubit) and spin-1 (qutrit) Heisenberg XY model separately, based on quantum discord (QD) and measurement-induced disturbance (MID) respectively. We find the evidence of the first- and second-order quantum phase transition (QPT) in both spin-1/2 and spin-1 systems. The effect of the temperature, magnetic field and Dzyaloshinskii–Moriya (DM) interactions on QPT and quantum correlation are also investigated. Finally, we observed that the QD and MID are not only vigorous for higher spin systems but also more robust than entanglement.

scholarly journals On the evolution and enhanced relaxation of a homogeneous isotropic two-dimensional plasma in a uniform magnetic field

1978 ◽  
Vol 19 (3) ◽  
pp. 411-436
Author(s):  
M. J. Haggerty
Keyword(s):  
Weak Coupling ◽  
Uniform Magnetic Field ◽  
Coupling Parameter ◽  
Pair Correlation ◽  
Three Dimensional ◽  
Collective Effects ◽  
Two Dimensional ◽  
Laboratory Plasmas ◽  
Large Factor ◽  
Careful Treatment

An enhancement of evolution rates in two-dimensional plasma models by a large factor containing the square root of the coupling parameter is known to occur. It is shown here to persist even when all collective effects are removed from weak-coupling calculations, under a simplified boundary condition preserving the isotropy of the system. Long-range vorticity is shown to develop. A careful treatment of time integrals allows irreversibility to be discussed with fewer ambiguities than usual with respect to limit ordering. Applications to three- dimensional laboratory plasmas are tentatively suggested. Future computer simulations should determine the usefulness of the comparatively simple relationships found among moments of the pair correlation. The new effects are shown to be qualitatively similar to some found in other approaches to plasma interactions in uniform magnetic fields.

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