Physicists show light beam swims upstream in quantum fluid

Study details publication findings

The research team published their results in the journal Physical Review A. They demonstrated that a beam of light can move upstream within a specific quantum fluid environment. This motion occurs by breaking action-reaction symmetry between the particles involved.

Mechanism involves non-reciprocal forces

The study explains that normal objects drift with a stream unless they use energy to oppose it. Light waves behave similarly but require an external force or active energy to move against the flow. In this experiment, internal interactions were converted into net momentum to achieve upstream motion.

Symmetry breaking explained

Newton's third law states that every action has an equal and opposite reaction. The researchers found that non-reciprocal interactions allow one object to influence another differently than the reverse. This difference in influence permits the light beam to swim against the current.