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The quantum Hall effect has long been suspected of superfluidity — the ability to flow without friction. Imagine a cook following a recipe: for each unit of magnetic flux, he must add exactly a certain number of electrons.

Electrons in an ultra-clean gallium arsenide film behave like a crowd at a crossroads, where the tilt of the magnetic field sets the direction. At zero tilt, they form a compressible liquid of composite fermions, particles made of an electron and a pair of vortices.