Ripples spreading across a calm lake after raindrops fall—and the way ripples from different drops overlap and travel outward—is one image that helps us picture how a quantum computer handles information.

Unlike conventional computers, which process digital data as “0 or 1,” quantum computers can process information in an in-between state where it is “both 0 and 1.” These quantum states behave like waves: they can overlap, reinforcing one another or canceling one another out. In computations that exploit this property, states that lead to the correct answer are amplified, while states that lead to wrong answers are suppressed.

Thanks to this interference between waves, a quantum computer can sift through many candidate answers at once. Our everyday computers take time because they evaluate each candidate one by one. Quantum computers, by contrast, can narrow down the answer in a single sweep—earning them the reputation of “dream machines” that could solve in an instant problem that might take hundreds of years on today’s computers.