The Uncertain Machine

A quantum computer does not compute the way any machine before it has computed. It stores information not as definite ones and zeros but as superpositions — blends of possibility held in suspension, made to interfere like waves, and collapsed into a single answer only at the instant you look. In the middle years of the 2020s, machines cooled to a hair above absolute zero are doing calculations that the largest supercomputers on earth could not finish before the sun burns out — and cryptographers are racing to replace the locks of the internet before these machines can break them.

This is the whole story, told whole: the failure of classical physics that cracked open the quantum world; the reclusive theorists and irrepressible showmen — Feynman, Deutsch, Shor — who dreamed the machine into being on paper; the thirty-year struggle to build it out of trapped ions, superconducting circuits, atoms held in light, and single particles of light; the near-miraculous invention of quantum error correction; the bitter "supremacy wars" over who had really beaten the classical competition; and the coming reckoning of Q-Day, when a large enough quantum computer will render today's encryption obsolete.

Written for the intelligent reader with no mathematics required, E.B Cohen tells the story of quantum computing honestly — neither the imminent miracle of the press releases nor the hoax of the debunkers, but a real and profound achievement, still short of usefulness, its ultimate destination genuinely unknown.