Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Experimental realization of a low-noise heralded single photon source   We present a heralded single-photon source with a much lower level of
unwanted background photons in the output channel by using the herald photon to
control a shutter in the heralded channel. The shutter is implemented using a
simple field programable gate array controlled optical switch.

19
The categories of this paper are: eess
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
37
The categories of this paper are: supr-con
2
The categories of this paper are: math
20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas
14
The categories of this paper are: math-ph
17
The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
0
The categories of this paper are: hep-ph
11
The categories of this paper are: hep-lat