Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cooperative parametric resonance of the spin one half system of the
  dense atomic gas   The cooperative resonance for a spin one half system interacting with dc and
ac magnetic field is considered. This interaction in the system collective
regime can result in parametic resonance and rapid excitation of the excited
spin state of the dense atomic gas. The phenomenon is studied using the density
matrix approach. We discuss the implementation of this effect and possible
applications of the quantum amplification by superradiant emission of
radiation.

8
The categories of this paper are: hep-ex
14
The categories of this paper are: math-ph
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
24
The categories of this paper are: dg-ga
11
The categories of this paper are: hep-lat
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
0
The categories of this paper are: hep-ph
23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
12
The categories of this paper are: nucl-th