Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ground-state and thermal entanglements in a non-Hermitian XY system with
  real and imaginary magnetic fields   In this manuscript, we study a non-Hermitian spin-1/2 XY system with two
sites in the presence of an alternating, imaginary and transverse magnetic
field. The eigenvalues and eigenstates of the Hamiltonian are exactly solved.
In addition, the energy spectrum of the system is discussed and an exceptional
point is obtained which distinguishes the parity-time reversal symmetry and
symmetry broken phases. Then we study the ground-state phase diagram which is
illustrated by a unit sphere with the anisotropic parameter gamma, reduced real
and imaginary magnetic fields (h0 and eta0) as variables, and find that there
are two possible ground states. We further discuss the ground-state concurrence
and find that it is only related to gamma and h0 when the value ranges of the
parameters are outside the sphere. Moreover, it only depends on eta0 and is
always the maximum when parameters are inside the sphere. When ground states
are degenerate, the entanglement of the pure state which consists of two ground
states is greater than that of the mixed state. We also study the thermal
entanglement and find that concurrence suddenly changes with temperature and
the reduced external magnetic fields (h0 and eta0). Especially, the change
fades away with increasing gamma. Furthermore, when temperature approaches
zero, there are overlapping parts between the thermal and non-degenerate
ground-state entanglements and it is indicated that the thermal entanglement is
realized by non-degenerate ground states.

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The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
29
The categories of this paper are: funct-an
16
The categories of this paper are: stat
14
The categories of this paper are: math-ph
10
The categories of this paper are: q-bio
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The categories of this paper are: q-fin
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The categories of this paper are: econ
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The categories of this paper are: comp-gas
2
The categories of this paper are: math
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The categories of this paper are: chem-ph
3
The categories of this paper are: physics
0
The categories of this paper are: hep-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: plasm-ph
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The categories of this paper are: nucl-ex