Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Probing the excitation spectrum of a Fermi gas in the BCS-BEC crossover
  regime   We measure excitation spectra of an ultracold gas of fermionic $^{40}$K atoms
in the BCS-BEC crossover regime. The measurements are performed with a novel
spectroscopy that employs a small modulation of the B-field close to a Feshbach
resonance to give rise to a modulation of the interaction strength. With this
method we observe both a collective excitation as well as the dissociation of
fermionic atom pairs in the strongly interacting regime. The excitation spectra
reveal the binding energy / excitation gap for pairs in the crossover region.

16
The categories of this paper are: stat
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
5
The categories of this paper are: gr-qc
2
The categories of this paper are: math
20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con