Download Observation of the Pairing Gap in a Strongly Interacting Quantum... Fermionic Atoms

Observation of the Pairing Gap in a Strongly Interacting Quantum Gas of
Fermionic Atoms
Cheng China , Markus Bartensteinb , Alexander Altmeyerb , Stefan Riedlb , Reece Geursenb , Selim Jochimb ,
Johannes Hecker Denschlagb , and Rudolf Grimmb
a
b
James Franck Institute, Department of Physics, University of Chicago, Chicago, IL 60637, USA
Institut für Experimentalphysik, Universität Innsbruck, A-6020 Innsbruck, Austria
The formation of composite bosons by pairing fermions leads to intriguing phenomena in physics, with
superconductivity and He-3 superfluidity being prominent examples. In an ultracold gas of fermionic
atoms, formation and condensation of diatomic molecules have been recently realized. This achievement
also opens up a new door to explore the crossover from a molecular Bose-Einstein condensate (BEC) to
a fermionic superfluid in the Bardeen-Cooper-Schrieffer (BCS) state.
We report on the observation of the pairing gap in a strongly interacting quantum gas of Li-6 atoms
based on radio-frequency spectroscopy 1 . Starting with a molecular Bose-Einstein condensate, we control
the interatomic interactions and find that the molecular binding energy in the BEC regime evolves into
the pairing gap in the BCS regime. The dependence of the pairing gap on the temperature and the Fermi
energy confirms the theoretical prediction and provides strong evidence that a molecular Bose-Einstein
condensate can be smoothly and adiabatically converted into a fermionic superfluid.
1
C. Chin, M. Bartenstein, A. Altmeyer, S. Riedl, S. Jochim, J. Hecker Denschlag, and R. Grimm,
Science 305, 1128 (2004); published online July 22 2004; 10.1126/science.1100818.
Sorting category: Aa Quantum gases, fluids and solids
Keywords: Bose-Einstein condensation, Fermionic superfluid, strong coupling, ultracold atom, Feshbach
resonance
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