Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Thermal Entanglement between Alternate Qubits of a Four-qubit Heisenberg
  XX Chain in a Magnetic Field   The concurrence of two alternate qubits in a four-qubit Heisenberg XX chain
is investigated when a uniform magnetic field B is included. It is found that
there is no thermal entanglement between alternate qubits if B is close to
zero. Magnetic field can induce entanglement in a certain range both for the
antiferromagnetic and ferromagnetic cases. Near zero temperature, the
entanglement undergoes two sudden changes with increasing value of the magnetic
field B. This is due to the changes in the ground state. This novel property
may be used as quantum entanglement switch. The anisotropy in the system can
also induce the entanglement between two alternate qubits.

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The categories of this paper are: eess
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The categories of this paper are: stat
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The categories of this paper are: solv-int
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The categories of this paper are: supr-con
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The categories of this paper are: astro-ph
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The categories of this paper are: hep-th
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The categories of this paper are: chem-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-fin
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The categories of this paper are: chao-dyn
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The categories of this paper are: dg-ga
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The categories of this paper are: ao-sci
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The categories of this paper are: alg-geom
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The categories of this paper are: physics
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The categories of this paper are: comp-gas