Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Why you should not use the electric field to quantize in nonlinear
  optics   We show that using the electric field as a quantization variable in nonlinear
optics leads to incorrect expressions for the squeezing parameters in
spontaneous parametric down-conversion and conversion rates in frequency
conversion. This observation is related to the fact that if the electric field
is written as a linear combination of bosonic creation and annihilation
operators one cannot satisfy Maxwell's equations in a nonlinear dielectric.

37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
29
The categories of this paper are: funct-an
18
The categories of this paper are: econ
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
12
The categories of this paper are: nucl-th
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
5
The categories of this paper are: gr-qc
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph