Quantum computers promise mathematical superpowers

AS THEY ZIP across the internet, passwords, bank transfers, emails and the like are protected from prying eyes by encryption. But no one is quite sure how reliable the technology is. Despite decades of trying, no-one has found a feasible way to break it. But at the same time, no-one has been able to prove such a method does not exist. In principle, a mathematician could have a brainwave tomorrow and bring the entire edifice of e-commerce—not to mention personal privacy—crashing down. In fact, something like that has already happened. In 1994 Peter Shor, an American mathematician, worked out how to reduce the time taken to break many types of encryption from billions of years to hours or less. The only snag was that “Shor’s algorithm”, as it is now known, required something that at the time only existed on university blackboards: a quantum computer. These days, quantum computers—which exploit quantum mechanics to perform some calculations far faster than ordinary computers—not only exist, but are attracting serious attention from investors. The market values of IonQ and Rigetti, two firms which have been listed since 2021 and 2022 respectively, are up seven- and four-fold since their debuts. In April McKinsey, a…