Bound quasiparticle transport along the edges of superfluid ³He

Superfluid ³He-B in a container naturally consists of two virtually isolated systems: the three-dimensional bulk of the superfluid, and a two-dimensional surface layer of Andreev-bound fermions. We discovered how to drive the bound fermions out of equilibrium and expel them into the bulk, where they can be observed [1].  Here we show that the quasiparticles not energetic enough to escape to bulk flow diffusively across macroscopic distances along the surface, demonstrating non-local dynamics that conserve energy and momentum. Similar two-dimensional confinement of electrons at a low temperature has led to the discovery of a variety of quantum Hall phases. Our work thus opens a research outlook ranging from Majorana fermions to composite objects between bound quasiparticles and topological defects or bosonic bulk excitations.