Martin Teichmann Atomes de lithium-6 ultra froids dans la ... - TEL

CHAPTER 5. EXPERIMENTAL RESULTS
accepted method to perform temperature dependent measurements.
The creation of vortices in a rotating gas is seen as a proof for its
superfluidity. The usual method to rotate a gas is to “stir” it using a
blue detuned laser beam. After having been used in bosonic gases
[148], it was used to show superfluidity of a fermionic gas at MIT [149].
Until now, this is the only direct proof of the superfluidity of the gas.
An interesting detail is that it seems not to be possible to image the
vortices in the crossover. They had to ramp the magnetic field to 74 mT,
well below the resonance point, during the expansion of the gas, in
order to observe vortices above 81 mT. Their explanation is that the
pairs will break during the expansion if they omit the described ramp.
This detection of vortices is also the technique that was used to observe
superfluidity in spin-polarized gases, mentioned in the last subsection.
The direct measurments of the pair correlation is possible by measuring
the correlations of the noise in the absorption images. This method
was introduced by the group at JILA [150]. They studied the noise correlations
of two images of the momentum distribution, one for each
spin state of the atoms. They dissociated weakly bound molecules in
the crossover, and were able to observe the correlation of the resulting
atoms in momentum space.
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