Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Comparison of spectral linewidths for quantum degenerate bosons and
  fermions   We observe a dramatic difference in optical line shapes of a $^4\text{He}$
Bose-Einstein condensate and a $^3\text{He}$ degenerate Fermi gas by measuring
the 1557-nm $2~^3S-2~^1S$ magnetic dipole transition ($8~\text{Hz}$ natural
linewidth) in an optical dipole trap. The $15~\text{kHz}$ FWHM condensate line
shape is only broadened by mean field interactions, whereas the degenerate
Fermi gas line shape is broadened to $75~\text{kHz}$ FWHM due to the effect of
Pauli exclusion on the spatial and momentum distributions. The asymmetric
optical line shapes are observed in excellent agreement with line shape models
for the quantum degenerate gases. For $^4$He a triplet-singlet s-wave
scattering length $a=+50(10)_{\text{stat}}(43)_{\text{syst}}~a_0$ is extracted.
The high spectral resolution reveals a doublet in the absorption spectrum of
the BEC, and this effect is understood by the presence of a weak optical
lattice in which a degeneracy of the lattice recoil and the spectroscopy photon
recoil leads to Bragg-like scattering.

28
The categories of this paper are: alg-geom
15
The categories of this paper are: nucl-ex
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
11
The categories of this paper are: hep-lat
37
The categories of this paper are: supr-con
36
The categories of this paper are: cmp-lg
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
10
The categories of this paper are: q-bio
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
31
The categories of this paper are: ao-sci