It’s been more than 40 years since the physicist Richard Feynman pointed out that building computing devices based on quantum principles could unlock powers far greater than those of “classical” computers. In a 1981 keynote speech often credited with launching the field of quantum computing, Feynman concluded with a now-famous quip:

“Nature isn’t classical, dammit, and if you want to make a simulation of nature, you’d better make it quantum mechanical.”

It’s been nearly 30 years since the mathematician Peter Shor came up with the first potentially transformative use for quantum computers. Much of the security of the digital world is built upon the assumption that factoring large numbers is a challenging and time-consuming task. Shor showed how to use qubits — quantum objects that can exist in mixtures of 0 and 1 — to do it in a heartbeat, at least relative to known classical methods.

Researchers feel quite confident (although not entirely certain) that Shor’s quantum algorithm beats all classical algorithms because — despite the tremendous incentives — no one has successfully broken modern encryption with a classical machine. But for tasks less glamorous than factoring, it’s hard to say for sure whether quantum methods are superior. Searching for further blockbuster applications has become something of a haphazard guessing game.

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