Alberto Tabarelli de Fatis

Ordinary light is a stream of independent particles: photons fly through each other without noticing their neighbors. But in superconducting circuits cooled to near absolute zero, the situation changes. There, photons travel along narrow metal tracks, and if tiny elements called Josephson junctions are embedded in these tracks, light begins to 'feel' itself.

In the quantum world, particles can merge into a single liquid that flows without friction. One of its most mysterious forms is the fractional quantum Hall liquid. In it, electrons or atoms move as a single vortex, and their charge splits into fractions, like a pie cut into perfectly equal slices.