A Boson/Fermion Mixture of Lithium Atoms

Z. Akdeniz, Patrizia Vignolo, M. P. Tosi

Jelena Stajic

Superfluidity At some of the coldest temperatures achieved in the laboratory, researchers can coax dilute gases of atoms into becoming a superfluid, with the whole gas behaving as one entity. Bosonic atoms, which like to congregate in one state, achieve this willingly. Fermions, which effectively repel each other, require more persuasion. Ferrier-Barbut et al. made a superfluid mixture of two gases, one made up of bosons and one of fermions. They used two isotopes of lithium, fermionic 6Li and bosonic 7Li. When they made the mixture oscillate, the two components took turns feeding energy into each other. Science , this issue p. [1035][1] [1]: /lookup/doi/10.1126/science.1255380

A. S. Alexandrov

Z. Akdeniz, Patrizia Vignolo, Anna Minguzzi +1 more

We use a semiclassical three-fluid model to analyse the conditions for spatial phase separation in a mixture of fermionic 6 Li and a (stable) Bose-Einstein condensate of 7 Li atoms under cylindrical harmonic confinement, both at zero and finite temperature. We show that with the parameters of the Paris experiment (Schreck F et al 2001 Phys. Rev. Lett. 87 080403) an increase of the boson-fermion scattering length by a factor five would be sufficient to enter the phase-separated regime. We give examples of configurations for the density profiles in phase separation and estimate that the transition should persist at temperatures typical of current experiments. For higher values of the boson-fermion coupling we also find a new phase separation between the fermions and the bosonic thermal cloud at finite temperature.

A. Trautmann

This thesis presents the investigation of the two-body scattering properties of cold atoms in \nsodium and lithium-sodium mixtures and their effects on the many body dynamics. Since both \nspecies are alkali atoms, the combined spin of both unpaired electrons can be either zero or one, \nproviding two different scattering channels. \nThe coupling of bound molecular states in these channels with the free atoms asymptote \ngives rise to the rich field of Feshbach resonance physics, where the interaction between the \nparticles can be controlled as an easily accessible experimental parameter. We have investigated \nthe Feshbach spectrum in the bosonic 7LiNa mixture and could confirm predictions based on \n6LiNa measurements, with a shift of the predicted spectrum by about 50 G. Also, the prospects \nof interaction tuning via Feshbach resonances were examined. \nThe difference of the scattering lengths of the electronic potentials also causes a coupling \nof atomic collisional channels, which can enable a spin exchange between the atoms. In this \nthesis, spin exchange processes have been studied in coherent oscillations in a thermal gas and \na Bose-Einstein condensate of sodium, as well as the evolution of this spinor gas into its ground \nstate. Preliminary studies of the heteronuclear spin exchange process in both the bosonic 7LiNa \nand in the fermionic-bosonic mixture 6LiNa are presented as well.

Arnout Jozef Ceulemans