Microtraps and waveguides for Bose-Einstein condensates

Abstract

Gaseous Bose-Einstein condensates containing up to 3 x 10⁶ ²³Na atoms were loaded into magnetic microtraps and waveguides on a microfabricated "atom chip" using optical tweezers. Single-mode propagation was observed along the waveguide. Closer to the microfabricated surface, perturbations to the waveguide potential spatially modulated the condensate density. The condensate lifetime was >[or equal to] 20 s and independent of the atom-surface separation, for separations >[or equal to] 70 [mu]m. Condensates were coherently split by deforming an optical single-well potential into a double-well potential. The relative phase between the two resulting condensates was determined from the matter wave interference pattern formed upon releasing the atoms from the separated potential wells. Coherent phase evolution was observed for condensates held separated by 13 [mu]m for <[or equal to ] 5 ms and was controlled by applying AC Stark shifts to either condensate. This demonstrated a trapped-atom interferometer. Vortices and spin textures were imprinted in spinor condensates using topological phases. The order parameter of condensates held in a Ioffe-Pritchard magnetic trap was manipulated by adiabatically varying the magnetic bias field along the trap axis. Fully inverting the axial bias field imprinted vortices in F = 1 and F = 2 condensates with 2h and 4h of angular momentum per particle, respectively. Reducing the axial bias field to zero distributed the condensate population across its 2F + 1 spin states, each with a different phase winding, and created a spin texture.

(cont.) Partially condensed atomic vapors were confined by a combination of gravitational and magnetic forces. They were adiabatically decompressed, by weakening the gravito-magnetic trap to a mean frequency of 1 Hz, then evaporatively reduced in size to 2500 atoms. This lowered the peak condensate density to 5 x 10¹⁰ atoms/cm³ and cooled the entire cloud in all three dimensions to a kinetic temperature of 450±80 pK.