Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electromagnetically Induced Transparency and slow light in media with
  Rydberg Excitons   We show that the Electromagnetically Induced Transparency (EIT) is possible
in a medium exhibiting Rydberg excitons and indicate the realistic parameters
to perform the experiment. The calculations for a Cu$_2$O crystal are given
which show that in this medium due to large group index one could expect
slowing down a light pulse by a factor about $10^4$.

6
The categories of this paper are: astro-ph
14
The categories of this paper are: math-ph
2
The categories of this paper are: math
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
11
The categories of this paper are: hep-lat
34
The categories of this paper are: chem-ph
36
The categories of this paper are: cmp-lg
15
The categories of this paper are: nucl-ex
31
The categories of this paper are: ao-sci
23
The categories of this paper are: solv-int
18
The categories of this paper are: econ
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph