IBM was home to one of these. A qubit is the information unit processed by a quantum computer. Physically, it can be represented by any quantum system that can exist in two different states. One choice of a qubit might be an electron spinning in a magnetic field. This phenomenon is known as superposition of states.
Entanglement is the other main quantum mechanical principle upon which quantum computing rests.
What makes this so strange is that, until one of the particles is measured, neither has a definite spin direction. Yet, as soon as one is measured and found, say, to be spin up, the other will be known to be in the spin-down state. While the probabilities of the outcome of a measurement can be calculated in advance, the actual result cannot be known beforehand. Intuitively, one would not expect a lack of predictability to be useful for computing, but superposition and entanglement are valuable because they generate a rapidly increasing number of states as more qubits come into play. Adding more qubits increases the register's capacity exponentially.