Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Z_2 Topological Insulators in Ultracold Atomic Gases   We describe how optical dressing can be used to generate bandstructures for
ultracold atoms with non-trivial Z_2 topological order. Time reversal symmetry
is preserved by simple conditions on the optical fields. We first show how to
construct optical lattices that give rise to Z_2 topological insulators in two
dimensions. We then describe a general method for the construction of
three-dimensional Z_2 topological insulators. A central feature of our approach
is a new way to understand Z_2 topological insulators starting from the
nearly-free electron limit.

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The categories of this paper are: math-ph
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The categories of this paper are: q-alg
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The categories of this paper are: q-bio
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The categories of this paper are: gr-qc
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The categories of this paper are: econ
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The categories of this paper are: comp-gas
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The categories of this paper are: chao-dyn
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The categories of this paper are: alg-geom
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ex
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The categories of this paper are: eess
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: adap-org
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The categories of this paper are: atom-ph