  We have investigated spin dynamics in a 2D quantum gas. Through spin-changing
collisions, two clouds with opposite spin orientations are spontaneously
created in a Bose-Einstein condensate. After ballistic expansion, both clouds
acquire ring-shaped density distributions with superimposed angular density
modulations. The density distributions depend on the applied magnetic field and
are well explained by a simple Bogoliubov model. We show that the two clouds
are anti-correlated in momentum space. The observed momentum correlations pave
the way towards the creation of an atom source with non-local
Einstein-Podolsky-Rosen entanglement.
