Qubit, or quantum bit, illustration. The qubit is a unit of quantum information. As a two-state system with superposition of both states at the same time, it is fundamental to quantum computing. The illustration shows the Bloch sphere. The north pole is equivalent to one, the south pole to zero. The other locations, anywhere on the surface of the sphere, are quantum superpositions of 0 and 1. When the qubit is measured, the quantum wave function collapses, resulting in an ordinary bit - a one or a zero - which effectively depends on the qubit's 'latitude'.