A superfluid gas behaves like a frictionless liquid. Two clouds of such gas are connected by a narrow bridge, and a stream of particles flows through it. This resembles the Josephson effect in superconductors, but here the particles are neutral atoms instead of electrons.
When an artificial magnetic field (created by lasers) is turned on, the atomic flow begins to swirl. Vortices inside the junction, Josephson vortices, line up in rows and change the current distribution. The critical current, at which superfluidity breaks down, is no longer constant: it rises and falls, repeating that striped pattern.
Simulations showed how the vortices, like whirlpools in a river, redistribute the flow. Unlike in superconductors, there is no electric charge here, so the pattern is distorted differently. This provides a new way to study coherence (wave consistency) in quantum systems. Such controllable junctions could become the basis for future quantum devices where information is carried not by electrons but by matter waves.
A synthetic magnetic field for neutral atoms is created by lasers — light makes particles move as if a real magnet were acting on them.
In Peter Watts's novel Blindsight, an alien intelligence uses magnetic fields to control quantum states — much like in this experiment.