Bidirectional propagation of cold atoms in a “stadium”-shaped magnetic guide

We demonstrate the bidirectional propagation of more than ${10}^7\mathrm{atoms}$ ${(}^{87}\mathrm{Rb})$ around a “stadium”-shaped magnetic ring that encloses an area of $10.9{\mathrm{cm}}^2$, with a flux density exceeding ${10}^{11}\text{atom}{\text{s}}^{-1}{\mathrm{cm}}^{-2}$. Atoms are loaded into the guide from a two-dimensional (and higher) magneto-optical trap at one side of the “stadium.” An optical standing wave pulse is applied to increase the propagation velocity of atoms along the waveguide. The atom sample fills the entire ring in $200\mathrm{ms}$ when counterpropagating atom sections of the original atom cloud recombine at their initial positions after a full revolution.