Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Collinear source of polarization-entangled photon pairs at
  non-degenerate wavelengths   We report on a simple but highly efficient source of polarization-entangled
photon pairs at non-degenerate wavelengths. The fully collinear configuration
of the source enables very high coupling efficiency into a single optical mode
and allows the use of long nonlinear crystals. With optimized dispersion
compensation it is possible to use a free-running laser diode as pump source
and to reach an entanglement fidelity of 99.4 % at rates as high as 27000
pairs/s per mW of pump power. This greatly enhances the practicality of the
source for applications in quantum communication and metrology.

10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
20
The categories of this paper are: acc-phys
21
The categories of this paper are: adap-org
32
The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
15
The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con