A QUANTUM LEAP

BACK IN 1994, WHEN QUANTUM COMPUTERS existed only as so much chalk on a blackboard, mathematician Peter Shor invented what may soon prove to be their killer app.

Shor trained his efforts on a calculation called “factoring,” which ordinarily nobody but a mathematician would care about, except it just happens to be an Achilles heel of the internet. If someone were to invent a computer that could perform this operation quickly, messages now hidden from hackers, terrorists, military adversaries, governments and competitors would be as easy to read as a Stephen King novel.

Shor, of course, didn’t have such a computer. He was writing an algorithm, or program, for a hypothetical machine that might one day exploit the weird properties of atoms and subatomic particles, as described by the theory of quantum mechanics, to perform calculations that conventional computers could only solve in years—maybe hundreds of years, or millions, or more time than the universe is expected to last. Too long, at any rate, to be useful in cracking open an email. Shor’s algorithm was a theoretical exercise. “The question of whether using quantum mechanics in a computer allows one to obtain more computational power,” he wrote in his 1994 paper, “has not yet been satisfactorily answered.”

The answers are now coming in.

Last year a team from Google achieved what it called “quantum supremacy” when its quantum computer performed a calculation faster than a conventional computer could. “Our machine performed the target computation in 200 seconds, and from measurements in our experiment we determined that it would take the world’s fastest supercomputer 10,000 years to produce a similar output,” wrote Google’s John Martinis and Sergio Boixo in a blog post. And earlier this month, a team under the direction of Pan Jianwei at the University of Science and Technology in China (USTC), in the journal , said its quantum computer