A standard computer bit has a 0 or a 1 state. A classical computer will manage 0 or 1, as the system chooses, but it remains limited to choosing 1 or (XOR) 0. It cannot manage both states at the same time.
A quantum computer is not constrained by an XOR state. It is an AND state. It can manage 0 and 1 at the same time until it is measured. A quantum state is unknown until observed, so a quantum program can use 0 and 1 at the same time. Once observed, the qubit will take a value of 0 or 1 because of the physical instability of a quantum state.
Just observing a quantum state makes the state break down. In quantum computing, this is called decoherence. It is not magic as some sci-fi hype suggests. Qubits are unstable. ...
