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Stabilizing polarized superfluid phases with optical lattices
Carlos Bolech
01.07.2011 at 10:15
A series of experiments on systems of trapped cold atomic gases were aimed at studying the
effects of polarization on superfluid pairing. Two different experimental groups encountered
surprising qualitative and quantitative discrepancies which seemed to be a function of the
confining geometry and the cooling protocol. Despite long familiarity with fermionic
superfluids, these observations had defied theoretical explanation. Using novel numerical
algorithms we study the solution space for a three-dimensional fully self-consistent mean-field
formulation of realistic systems with up to 100,000 atoms. Our studies demonstrate a tendency
towards metastability as the geometry is elongated and suggest an explanation for the observed
discrepancy. From our calculations, the most likely solution which is consistent with the
experiments at high aspect ratio supports a state strikingly similar to the so called FFLO state
(after Ferrell, Fulde, Larkin and Ovchinnikov), which had been theorized but eluded detection
so far.
Moreover, this scenario is consistent with the predictions for one-dimensional systems of dilute
polarized attractive gases, and yet another set of cold-atom experiments use optical lattices to
test this limit. The measurements are in quantitative agreement with theoretical calculations
(using a wide array of numerical and analytic techniques) in which a partially polarized phase is
found to be the 1D analogue of the FFLO state.
More calculations and experiments are under way, testing the inter-dimensional stability and
crossover.
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