Ultracold quantum matter

Abstract:

We report on the realization of a stiff magnetic trap with independently adjustable trap frequencies, ω-z$/ and ω-r$/ in the axial and radial directions, respectively. This has been achieved by applying an axial modulation to a time-averaged orbiting potential (TOP) trap. The frequency ratio of the trap, ω-z$//ω-r$/, can be decreased continuously from the original TOP trap value of 2.83 down to 1.6. We have transferred a Bose-Einstein condensate (BEC) into this trap and obtained very good agreement between its observed anisotropic expansion and the hydrodynamic predictions. Our method can be extended to obtain a spherical trapping potential, which has a geometry of particular theoretical interest.

Abstract:

A novel dipole force trap was developed for trapping caesium atoms in the lower hyperfine level of the ground state and in preliminary experiments a cloud of ≈1000 atoms was trapped. The viability of the trap is discussed, including suggestions for amendments to the trap design and problems that might occur which are intrinsic to the caesium atom.

Abstract:

We report the observation of harmonic generation and strong nonlinear coupling of two collective modes of a condensed gas of rubidium atoms. Using a modified time averaged orbiting potential trap we changed the trap anisotropy to a value where the frequency of the m = 0 high-lying mode corresponds to twice the frequency of the m = 0 low-lying mode, thus leading to strong nonlinear coupling between these modes. By changing the anisotropy of the trap and exciting the low-lying mode we observed significant frequency shifts of this fundamental mode and also the generation of its second harmonic.