Bose-Bose mixtures in reduced dimensions

The two-body scattering is greatly modified in reduced dimensions. With ultracold atoms, low dimensional configurations are routinely accessible thanks to the use of optical lattices which allow confinements sufficiently strong to freeze the motion along chosen directions. With two different atomic species, we use a species-selective optical potential, in the form of a standing wave, to confine only one species in 2D disks and study the scattering between particles existing in different dimensions, i.e., we realize a 2D-3D mix-dimensional configuration, reminiscent of a brane world. We review the scattering theory specific to this configuration and derive an effective scattering length a(eff) in terms of the free-space scattering length a and the confinement parameters. We detect experimentally the enhancement of inelastic collisions arising at particular values of a and relate these values to the divergences of a(eff). Unlike the confinement-induced resonances predicted and observed for identical particles, our mixed-dimensional resonances occur in a series of several resonances, because the relative and centre-of-mass motion are coupled.