Adbhut Gupta

In a thin sandwich of gallium arsenide, electrons don't behave like individual balls but like a single quantum liquid. If the layer is made just 70 nanometers thick, this liquid separates into two nearly independent flows, like oil on water.

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.