Jessica Richter

A quantum dot is a box so small that an electron inside cannot have just any energy, but only strictly defined values, like the steps of a staircase. Each step can accommodate several electrons, but exactly how many is the question. If a step is double, two electrons can stand on it; if single, only one.

In a narrow corridor, people walk in rows rather than as a crowd. The number of rows depends on the width of the passage. In graphene, this corridor is a quantum point contact — a constriction where electrons move ballistically without scattering.