Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum crossover in moderately damped epitaxial NbN/MgO/NbN junctions
  with low critical current density   High quality epitaxial NbN/MgO/NbN Josephson junctions have been realized
with MgO barriers up to a thickness of d=1 nm. The junction properties
coherently scale with the size of barrier, and low critical current densities
down to 3 A/cm$^2$ have been achieved for larger barriers. In this limit,
junctions exhibit macroscopic quantum phenomena for temperatures lower than 90
mK. Measurements and junction parameters support the notion of a possible use
of these devices for multiphoton quantum experiments, taking advantage of the
fast non equilibrium electron-phonon relaxation times of NbN.

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The categories of this paper are: acc-phys
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The categories of this paper are: supr-con
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The categories of this paper are: alg-geom
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The categories of this paper are: math-ph
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The categories of this paper are: adap-org
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The categories of this paper are: hep-lat
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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: quant-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: chem-ph