Condensate Produces Atomic Solitons

Researchers at Rice University in Houston have further explored the wave nature of matter by generating atomic solitons from a lithium Bose-Einstein condensate. The scientists, who described the work in the May 9 issue of Nature, created the first lithium Bose-Einstein condensate in 1995.

The researchers evaporatively cooled the ⁷Li atoms in a magnetic trap to 1 µK and then moved those in the (F, m_F) = (2,2) state into an optical trap created with a pair of Nd:YAG lasers. They exposed the atoms to a 15-ms microwave pulse, which transferred 98 percent of them to the (1,1) state, and again cooled the sample to form a condensate of 3 x 10⁵ atoms, applying a magnetic field such that the scattering length of the atoms was small and either positive or negative.

By displacing the red-detuned, radial confinement laser beam and turning off the blue-detuned, axial confinement beams, the team created trains of up to 15 solitons for atoms with a negative scattering length that oscillated in an effective one-dimensional potential over a 740-µm span for several seconds before degrading. The solitons obey the same nonlinear Schrödinger equation as optical solitons in a fiber with a self-focusing third-order nonlinearity, said Randall G. Hulet, one of the researchers on the project.