The smallest unit of information in a computer is the bit: on or off, 1 or 0. Today, the world's entire computing power is built on the combination and interconnection of countless ones and zeros. Quantum computers have their own version of the bit: the qubit. It, too, has two basic states. The main difference: Quantum effects allow a superposition of the two states, so that the qubit is not either 1 or 0, but both at the same time. With different proportions of 0 and 1, the qubit can theoretically assume an infinite number of states.