Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Non-classical photon pair generation in atomic vapours   A scheme for the generation of non-classical pairs of photons in atomic
vapours is proposed. The scheme exploits the fact that the cross correlation of
the emission of photons from the extreme transitions of a four-level cascade
system shows anti-bunching which has not been reported earlier and which is
unlike the case of the three level cascade emission which shows bunching. The
Cauchy-Schwarz inequality which is the ratio of cross-correlation to the auto
correlation function in this case is estimated to be $10^3-10^6$ for
controllable time delay, and is one to four orders of magnitude larger compared
to previous experiments. The choice of Doppler free geometry in addition to the
fact that at three photon resonance the excitation/deexcitation processes occur
in a very narrow frequency band, ensures cleaner signals.

24
The categories of this paper are: dg-ga
5
The categories of this paper are: gr-qc
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
7
The categories of this paper are: hep-th
21
The categories of this paper are: adap-org
20
The categories of this paper are: acc-phys
36
The categories of this paper are: cmp-lg
19
The categories of this paper are: eess
23
The categories of this paper are: solv-int
6
The categories of this paper are: astro-ph