Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Topological quantization in units of the fine structure constant   Fundamental topological phenomena in condensed matter physics are associated
with a quantized electromagnetic response in units of fundamental constants.
Recently, it has been predicted theoretically that the time-reversal invariant
topological insulator in three dimensions exhibits a topological
magnetoelectric effect quantized in units of the fine structure constant
$\alpha=e^2/\hbar c$. In this work, we propose an optical experiment to
directly measure this topological quantization phenomenon, independent of
material details. Our proposal also provides a way to measure the
half-quantized Hall conductances on the two surfaces of the topological
insulator independently of each other.

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The categories of this paper are: gr-qc
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The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
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The categories of this paper are: nlin
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
1
The categories of this paper are: cs
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: eess
33
The categories of this paper are: plasm-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: q-alg
36
The categories of this paper are: cmp-lg
31
The categories of this paper are: ao-sci