Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Optimal design and quantum limit for second harmonic generation in
  semiconductor heterostructures
5
The categories of this paper are: gr-qc
16
The categories of this paper are: stat
12
The categories of this paper are: nucl-th
18
The categories of this paper are: econ
20
The categories of this paper are: acc-phys
11
The categories of this paper are: hep-lat
37
The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
26
The categories of this paper are: bayes-an
6
The categories of this paper are: astro-ph
7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
32
The categories of this paper are: atom-ph
13
The categories of this paper are: quant-ph