Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Practical long-distance quantum communication using concatenated
  entanglement swapping
21
The categories of this paper are: adap-org
4
The categories of this paper are: cond-mat
3
The categories of this paper are: physics
37
The categories of this paper are: supr-con
24
The categories of this paper are: dg-ga
16
The categories of this paper are: stat
14
The categories of this paper are: math-ph
11
The categories of this paper are: hep-lat
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
2
The categories of this paper are: math
29
The categories of this paper are: funct-an
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex