Quantum Computers Bust Problem Conventional Computers Can't Solve

Fluorescent lights emerge from the University of Maryland quantum simulator, revealing the results of the experiment.
Credit: University of Maryland

By Rafi Letzter in Live Science

Fifty-odd atoms buzz through a pocket of empty space. Invisible lines of force — quantum magnetism — chain them together. Jiggle one, the others jiggle in sympathy. Ring another like a bell and the others will pick up the song at a different pitch or a slower speed. Every action on any one atom impacts each other atom in the 50. It's a tiny world of unfolding subtlety and complexity.

There are limits in our larger world that make such jiggles tricky to predict. For instance, nothing moves faster than the speed of light and no frozen point gets colder than absolute zero. Here's another limit: Our clunky, classical computers can't predict what will happen in that little world of 50 interacting atoms.

The problem isn't that our computers aren't big enough; if the number were 20 atoms, you could run the simulation on your laptop. But somewhere along the way, as the small world swells to include 50 atoms, the problem of predicting how they'll behave too difficult for your laptop, or any normal computer, to solve. Even the biggest conventional supercomputer humanity will ever build would lose itself forever in a labyrinth of calculations — whatever answer it might eventually spit out might not come until long after the heat death of the universe.

And yet, the problem has just been solved.

Twice, actually.

Two laboratories, one at Harvard and one at the University of Maryland (UMD), built machines that can simulate quantum magnetism at this scale.

Their results, published as twin papers Nov. 29 in the journal Nature, demonstrate capabilities of two special quantum computers that leap far beyond what any conventional or quantum computer previously built has been able to accomplish.

Referring to the machine in his laboratory, Mikhail Lukin, one of the leaders of the Harvard team, told Live Science that "It's basically a quantum simulator."

That means the computer is built for a specific task: to study the evolution of quantum systems. It won't be breaking encryption codes on the world's banks, finding the highest mountain in a mountain range or pulling off any of the other tasks for which general quantum computers are suited.

Instead, the Harvard and UMD machines are really good at solving a particular kind of problem: If a complicated quantum system starts in one state, how will it move and evolve?

It's a narrow question, but in solving it, the researchers are developing technologies and making new discoveries in physics that will allow for even more complicated computers, which will pull off even more impressive tasks.

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