A "quantum bit," used in quantum computing. Quantum mechanics allows for a qubit to be both zero and one at the same time, and hence to store two possible numbers (zero and one) simultaneously. N qu-bits store 2N possible numbers, thus is able to perform 2N possible solutions to a problem simultaneously. This is what gives the quantum computer its enormous power. Measurement is via quantum decoherence, which causes the qubit to collapse into a standard binary state of either zero or one.