Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Superradiant Emission of Ultra-Bright Photon Pairs in Doppler-Broadened
  Atomic Ensemble   With a recent rising interest of single photon superradiance due to its
potential usefulness for efficient collection of single photon from an atomic
ensemble, bright and narrow photon pair source is a key component in
realization of quantum communication and quantum computer based on coherent
interaction between light and atomic ensemble. We report the superradiant
emission of ultra-bright photon pairs with a coincidence counting rate per
input power of 64,600 cps/mW via spontaneous four-wave mixing in a thermal
vapour cell. The photon-pair generation rate is enhanced by the contribution of
two-photon coherence of almost atomic velocity groups in the Doppler-broadened
ladder-type atomic system. The quadratic proportionality of the probability of
detecting a heralded single photon as a function of the optical depth clarifies
that the ultra-brightness results from the superradiance. In addition, a single
photon superradiant beating at a high optical depth of the atomic ensemble is
observed for the first time.

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The categories of this paper are: comp-gas
8
The categories of this paper are: hep-ex
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The categories of this paper are: funct-an
16
The categories of this paper are: stat
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The categories of this paper are: bayes-an
7
The categories of this paper are: hep-th
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
11
The categories of this paper are: hep-lat
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The categories of this paper are: chem-ph
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The categories of this paper are: eess
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The categories of this paper are: nucl-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: plasm-ph
2
The categories of this paper are: math
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The categories of this paper are: cmp-lg