Preparing topological states of a Bose-Einstein condensate

Observations of lose-Einstein condensates-macroscopic populations of ultrac old atoms occupying a single quantum state-in dilute alkali-metal and hydro gen gases have stimulated a great deal of research into the statistical phy sics of weakly interacting quantum degenerate systems(1,2). Recent experime nts offer a means of exploring fundamental low-temperature physics in a con trollable manner. A current experimental goal in the study of trapped Bose gases is the observation of superfluid-like behaviour, analogous to the per sistent currents seen in superfluid liquid helium which now without observa ble viscosity. The 'super' properties of Bose-condensed systems occur becau se the macroscopic occupation of a quantized mode provides a stabilizing me chanism that inhibits decay through thermal relaxation(3). Here we show how to selectively generate superfluid vortex modes with different angular mom enta in a Bose-Einstein condensate. Our approach involves solving the time- dependent equation of notion of a two-component condensate with strongly co upled internal atomic states, as recently investigated experimentally(4,5). The generation of vortices relies on the coupling between the states (achi eved by applying an electromagnetic field), combined with mechanical rotati on of the trapping potentials which confine the condensate.