  We have realized a conical matter wave lens. The repulsive potential of a
focused laser beam was used to launch a Bose-Einstein condensate into a
radially expanding wavepacket whose perfect ring shape was ensured by energy
conservation. In spite of significant interactions between atoms, the spatial
and velocity widths of the ring along its radial dimension remained extremely
narrow, as also confirmed by numerical simulations. Our results open the
possibility for cylindrical atom optics without the perturbing effect of
mean-field interactions.
