Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Generation of polarization-entangled photon pairs in a cascade of two
  type-I crystals pumped by femtosecond pulses   We report the generation of polarization-entangled photons by
femtosecond-pulse-pumped spontaneous parametric down-conversion in a cascade of
two type-I crystals. Highly entangled pulsed states were obtained by
introducing a temporal delay between the two orthogonal polarization components
of the pump field. They exhibited high-visibility quantum interference and a
large concurrence value, without the need of post-selection using
narrow-bandwidth-spectral filters. The results are well explained by the theory
which incorporates the space-time dependence of interfering two-photon
amplitudes if dispersion and birefringence in the crystals are appropriately
taken into account. Such a pulsed entangled photon well localized in time
domain is useful for various quantum communication experiments, such as quantum
cryptography and quantum teleportation.

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The categories of this paper are: cond-mat
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The categories of this paper are: atom-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-lat
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The categories of this paper are: nlin
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: comp-gas
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The categories of this paper are: plasm-ph
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The categories of this paper are: eess
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
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The categories of this paper are: funct-an