Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hidden-symmetry-protected quantum pseudo-spin Hall effect in optical
  lattices   We propose a scheme to realize a new Z_2 topological insulator in a square
optical lattice. Different from the conventional topological insulator
protected by the time-reversal symmetry, here, the optical lattice possesses a
novel hidden symmetry, which is responsible for the present Z_2 topological
order. With a properly defined pseudo-spin, such a topological insulator is
characterized by the helical edge states which exhibits pseudo-spin-momentum
locking, so that it can be considered as a quantum pseudo-spin Hall insulator.
The Z_2 topological invariant is derived and its experimental detection is
discussed as well.

6
The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
18
The categories of this paper are: econ
0
The categories of this paper are: hep-ph
23
The categories of this paper are: solv-int
11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
37
The categories of this paper are: supr-con
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
29
The categories of this paper are: funct-an
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
12
The categories of this paper are: nucl-th
13
The categories of this paper are: quant-ph
19
The categories of this paper are: eess