Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photonic crystal optics in cold atomic gases   We describe propagation of light in a gas with periodic density modulation,
demonstrating photonic-crystal-like refraction with negative refraction angles.
We address the role of poorly defined boundaries and damping, and derive an
optical analog of the quantum adiabatic theorem. For Cs atoms in an optical
lattice, we show that relying on semi-adiabatic propagation one can excite and
spatially split positively and negatively refracting modes at experimentally
available gas densities.

20
The categories of this paper are: acc-phys
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
28
The categories of this paper are: alg-geom
30
The categories of this paper are: q-alg
23
The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
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The categories of this paper are: adap-org
37
The categories of this paper are: supr-con
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The categories of this paper are: econ
31
The categories of this paper are: ao-sci
29
The categories of this paper are: funct-an
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The categories of this paper are: eess
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin