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What they can say for sure is that the system doesn’t use simulated annealing, which is essentially a means of searching for a mathematical solution. According to Lidar, simulated annealing is akin to looking for the lowest possible point in a vast landscape.
“We call it an energy landscape,” he says. “There is a solution hiding somewhere in that landscape, and you can imagine that solution is hiding at the lowest point on the surface. You’re trying to find that lowest point.” This is done by randomly traveling across the landscape, moving down “hills” and back up them, until you locate the deepest valley.
This strategy relies purely on classical physics, not quantum physics. But Lidar says the D-wave is “consistent” with quantum annealing. This is similar to simulated annealing — except you can, in essence, go through the hills rather than over them. “You can take advantage of a quantum phenomenon called tunneling,” Lidar says. “It’s like a quantum shortcut.” He’s careful to say that he and his team have not proven that the D-Wave uses quantum annealing, but the system certainly appears to use it.