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Seminars:  September 2008

• Thu 9/25, 3:30PM in Room 184                   print event

  Thomas Killian
  Ultracold Strontium: Studies of Collisional Properties and Progress towards Quantum Degeneracy

  Alkaline-earth atoms such as strontium and atoms with similar valence electronic structure differ significantly from alkali-metal atoms that are typically used in ultracold experiments. They have a closed-shell ground state structure, numerous isotopes including spinless bosons, and metastable triplet levels that lead to novel laser-cooling techniques and interactions. They present many new opportunities for the study and application of ultracold atoms, such as optical frequency standards, long-coherence-time interferometers, optical Feshbach resonances with little induced loss, and Bose and Fermi quantum degenerate gases and mixtures. I will describe recent experiments with two-photon spectroscopy of ground molecular levels that have accurately determined the s-wave scattering lengths for all strontium isotopes. This has guided our recent progress towards quantum degeneracy. We have also developed techniques for populating metastable levels in an optical dipole trap and studied collisional properties of these states. Finally, I will discuss prospects to use an optical Feshbach resonance in quantum degenerate strontium to stabilize solitons in 2-two dimensions and study quantum gases with disordered nonlinear interactions. This work is supported by the National Science Foundation, Welch Foundation, and the David and Lucille Packard Foundation. * In collaboration with Y. Natali Martinez de Escobar, Pascal Mickelson, and Mi Yan.

• Thu 9/11, 3:30PM in Room 184                   print event

  Kris Helmerson
  Vortices and persistent currents: Observations in topologically constrained Bose-Einstein condensates

  Recent studies of both 1-D and 2-D weakly-interacting, atomic Bose-Einstein condensates have demonstrated a number of interesting phenomena including a Tonks-Girardeau gas and the Berezinskii-Kosterlitz-Thouless crossover, respectively. Clearly, reduced dimensionality or topological constraints enables the observation of new and interesting phenomena. I will describe recent experiments on the confinement of a sodium Bose-Einstein condensate in a toriodal-shaped trap and also in a flat optical trap to produce a ring-shaped and 2-D quantum degenerate gas, respectively. We have been able to observe a number of phenomena connected with the superfluid transition in such systems, such as persistent currents and quasi-condensate formation.