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Effects of disorder in ultra-cold gases

Ziel

The project is devoted to the theoretical study of disordered ultra-cold gases. We focus on two problems:
1. BOSE-EINSTEIN CONDENSATION NEAR RESONANT IMPURITIES: by tuning the atom-impurity scattering length near a Feshbach resonance, atoms can be trapped into a bound state localized around the impurity. We first solve (exactly) the problem of two interacting bosons in the presence of the impurity using Green functions. We then write an ansatz for the many-bosons condensate wavefunction and calculate the energy spectrum of elementary excitations. We determine the limiting number of bosons above which the condensate is unstable due to the repulsive boson-boson interaction and estimate the lifetime of the condensate against decay due to inelastic processes. Finally, we consider many impurities randomly distributed on an optical lattice. We derive an effective low-energy lattice Hamiltonian and we investigate the resulting quantum phase diagram numerically.
2. DISORDER EFFECTS IN FERMI SUPERFLUIDS: starting from the Bogoliubov-De Gennes equations of BCS theory, we investigate the local properties of the gas near a single impurity. We calculate the energy spectrum of quasiparticles and the spatial profiles of the atoms density and the gap parameter. We then discuss the effects of a quenched disorder on the condensate fraction and super-fluid density of the gas across the BEC-BCS crossover. We discuss explicitly the most interesting case of tuning the fermion-impurity scattering length near a resonance. The formation of bound states fermion-impurity is detrimental to super-fluidity, as it breaks Cooper pairs. We generalise the Abrikosov and Gorkov theory for superconductors with paramagnetic impurities to this novel system. We calculate energy gap and super-fluid density as a function of impurity concentrations and scattering lengths. Finally we discuss methods to detect the predicted gapless super-fluid phase in trapped Fermi gases.

Wissenschaftliches Gebiet (EuroSciVoc)

Schlüsselbegriffe

Thema/Themen

Aufforderung zur Vorschlagseinreichung

FP6-2005-MOBILITY-5
Andere Projekte für diesen Aufruf anzeigen

Finanzierungsplan

EIF - Marie Curie actions-Intra-European Fellowships

Koordinator

LABORATOIRE DE PHYSIQUE THEORIQUE ET MODELES STATISTIQUES
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