Thermal entanglement of two interacting qubits in a static magnetic field |
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Authors: | G Lagmago Kamta A Y Istomin A F Starace |
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Institution: | (1) Laboratoire de Chimie Théorique, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Quebec, J1K 2R1, Canada;(2) Department of Physics and Astronomy, The University of Nebraska, 116 Brace Laboratory, Lincoln, NE 68588-0111, USA |
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Abstract: | 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. |
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Keywords: | 03 65 Ud Entanglement and quantum nonlocality 03 67 -a Quantum information 03 67 Mn Entanglement production characterization and manipulation 75 10 Jm Quantized spin models |
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