Just as a leaf drifts along with a stream, objects in other moving fluids normally drift along with the flow. That is, unless they exert energy to move against it. Although it may be less intuitive, light waves or photons work similarly. To move against a stream of light, an object or particle, like a photon, must either have an external force acting on it or actively use energy to move upstream.

In a new study, published in Physical Review A, a team of physicists demonstrates how a beam of light can “swim” upstream in a quantum fluid of light by breaking action-reaction symmetry and reshaping how the surrounding forces affect the flow.