Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Description of thermal entanglement with the static path plus
  random-phase approximation   We discuss the application of the static path plus random phase approximation
(SPA+RPA) and the ensuing mean field+RPA treatment to the evaluation of
entanglement in composite quantum systems at finite temperature. These methods
involve just local diagonalizations and the determination of the generalized
collective vibrational frequencies. As illustration, we evaluate the pairwise
entanglement in a fully connected XXZ chain of $n$ spins at finite temperature
in a transverse magnetic field $b$. It is shown that already the mean field+RPA
provides an accurate analytic description of the concurrence below the mean
field critical region ($|b|<b_c$), exact for large $n$, whereas the full
SPA+RPA is able to improve results for finite systems in the critical region.
It is proved as well that for $T>0$ weak entanglement also arises when the
ground state is separable ($|b|>b_c$), with the limit temperature for pairwise
entanglement exhibiting quite distinct regimes for $|b|<b_c$ and $|b|>b_c$.

37
The categories of this paper are: supr-con
34
The categories of this paper are: chem-ph
25
The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
17
The categories of this paper are: q-fin
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org
9
The categories of this paper are: nlin
24
The categories of this paper are: dg-ga
2
The categories of this paper are: math
8
The categories of this paper are: hep-ex
26
The categories of this paper are: bayes-an