Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Instabilities and the roton spectrum of a quasi-1D Bose-Einstein
  condensed gas with dipole-dipole interactions   We point out the possibility of having a roton-type excitation spectrum in a
quasi-1D Bose-Einstein condensate with dipole-dipole interactions. Normally
such a system is quite unstable due to the attractive portion of the dipolar
interaction. However, by reversing the sign of the dipolar interaction using
either a rotating magnetic field or a laser with circular polarization, a
stable cigar-shaped configuration can be achieved whose spectrum contains a
`roton' minimum analogous to that found in helium II. Dipolar gases also offer
the exciting prospect to tune the depth of this `roton' minimum by directly
controlling the interparticle interaction strength. When the minimum touches
the zero-energy axis the system is once again unstable, possibly to the
formation of a density wave.

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The categories of this paper are: mtrl-th
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The categories of this paper are: atom-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: q-bio
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The categories of this paper are: acc-phys
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The categories of this paper are: chao-dyn
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: plasm-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: cs
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The categories of this paper are: nlin
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The categories of this paper are: adap-org
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The categories of this paper are: patt-sol
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The categories of this paper are: ao-sci
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The categories of this paper are: econ