For nearly a century, we have been computing on technologies governed by a physics no one has truly understood, quantum mechanics, yet using a strictly binary logic. In 1935, Einstein himself refused to accept its strangeness. A year later, Alan Turing imagined a single machine able to carry out any calculation a human could, the theoretical blueprint of every computer that followed, and in the same stroke he traced the outer limits of what computation can ever reach.
 

The first real machines, built a decade later, were designed in part to break wartime codes, the very task quantum computer may one day master again. In 1981, Richard Feynman identified a different wall: even within those limits, our classical machines cannot efficiently simulate the way nature actually behaves, and the way through was to build a machine that is itself quantum.