Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photon number conservation and photon interference   The group theoretical aspect of the description of passive lossless optical
four-ports (beam splitters) is revisited. It is shown through an example, that
this approach can be useful in understanding interferometric schemes where a
low number of photons interfere. The formalism is extended to passive lossless
optical six-ports, their SU(3)-theory is outlined.

36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
23
The categories of this paper are: solv-int
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
15
The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
28
The categories of this paper are: alg-geom
1
The categories of this paper are: cs
3
The categories of this paper are: physics
9
The categories of this paper are: nlin
24
The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph