Quantum Supremacy: How the Quantum Computer Revolution Will Change Everything

by Michio Kaku

Atoms are like spinning tops. In a magnetic field, they can align either up or down with respect to the magnetic field, which can correspond to a 0 or a 1. The power of a digital computer is related to the number of states (the 0s or 1s) you have in your computer. But due to the weird rules of the subatomic world, atoms can also spin in any combination of the two. For example, you can have a state in which the atom spins up 10 percent of the time and spins down 90 percent of the time. Or it spins up 65 percent of the time and spins down 35 percent of the time. In fact, there are an infinite number of ways that you can have an atom spin. This vastly increases the number of states that are possible. So the atom can carry much more information, not just in a bit, but a qubit, i.e., a simultaneous mixture of the up and down states. Digital bits can only carry one bit of information at a time, which limits their power, but qubits, or quantum bits, have almost unlimited power. The fact that, at the atomic level, objects can exist simultaneously in multiple states is called superposition. (This also means the familiar laws of common sense are routinely violated at the atomic level. At that scale, electrons can be in two places at the same time, which is not true for large objects.) In addition, these qubits can interact with each other, which is not possible for ordinary bits. This is called entanglement. Whereas digital bits have independent states, each time you add another qub...