hide captionGoogle and NASA are betting that quantum forces are at work inside D-Wave's 512-bit chip.
Courtesy of D-Wave
It's exactly the sort of futuristic thinking you'd expect from Google and NASA: Late last week, the organizations announced a partnership to build a Quantum Artificial Intelligence Lab at NASA's Ames Research Center.
But questions surround the new type of computer at the lab's core. D-Wave systems, the company that makes the machine, says it is a quantum computer — a machine that runs on the strange laws of quantum mechanics. But although the computer can solve a certain type of problem much faster than conventional computers, critics say that the company's claims are not supported by scientific evidence.
"It's not exactly science, what they're doing," says Christopher Monroe, a physicist with the Joint Quantum Institute at the University of Maryland. "It's high-level engineering, and I think it's high-level salesmanship, too."
The quantum computer is a giant black box, or more precisely, a black cube approximately 10 feet on a side. Inside is a refrigeration system that chills the guts to near absolute zero, and shields the workings to protect them from external radiation.
hide captionThe D-Wave processor must be shielded from outside interference inside an ultra-cold refrigerator in order to enter a quantum state.
Courtesy of D-Wave
In this rarefied environment, the laws of quantum mechanics can come into effect. These quantum rules are pretty strange. Particles can be in two opposite states at once, and they can be intrinsically tied together through a process known as "entanglement." For example, two quantum coins could be in a state of heads and tails simultaneously, as though they were flipping through the air. If the two coins were entangled, reading "heads" on one after the flip would instantly tell you that the other was heads — even if it were on the other side of the galaxy.
The D-Wave Two computer has 512 quantum "bits," or units of information, in its supercooled central processor that can be entangled together, according to the company. The entanglement allows the computer to do things that a conventional computer can't. In particular, it's good at choosing between many different solutions to a problem, according to Geordie Rose, D-Wave's chief technology officer.
Here's (roughly) how it works: Just like quantum coins, the quantum bits exist in two states at once, and because they are entangled, that means the entire chip is simultaneously in many different configurations of "heads and tails." The quantum computer, in a sense, simultaneously tries every answer imaginable before settling on an efficient one. Running the computer just a few times will give a subset of highly efficient solutions. By contrast, a conventional computer would have to individually test millions or billions of solutions to find the right answer.
Rose says that the new machine won't always be better than a regular computer, but for machine learning and searching — activities both Google and NASA are interested in — the D-wave's computer could be far more effective.
"The best answer, or the highest or the lowest or the smallest or the meatiest ... no matter what," Rose says. "If it's got an '-iest' at the end and you can write down a mathematical equation for what you mean about that, then you can attack it with one of our machines."
But proving exactly what D-Wave's computer does is tricky. Quantum states are highly sensitive to outside intrusion. The very act of trying to measure entanglement can easily destroy it.
There is solid evidence that the D-Wave machine is unusual. New research by computer scientist Catherine McGeoch at Amherst College suggests it can solve one particular kind of problem thousands of times faster than a regular computer. But McGeoch adds that the D-Wave Two was not measurably faster at solving two other types of problems tested.
And work from the lab of John Martinis, a researcher at the University of California, Santa Barbara, also seems to hint at quantum processes at work inside D-Wave's previous generation of quantum chip, the D-Wave One.
But Monroe remains skeptical. He believes that the D-Wave team has never demonstrated that entanglement is happening on the chips in its machine. He believes that D-Wave's supposedly quantum bits are actually working instead as tiny electromagnets. Those magnets, Monroe believes, could be interacting in ways to solve a certain problem very quickly without quantum mechanics. "There's no evidence that what they're doing has anything to do with quantum mechanics," he says. If he's right, then D-Wave's machine may be far more narrow in its abilities than the company believes.
D-Wave's Geordie Rose acknowledges the criticism, but says he believes that D-Wave's machine ultimately will also prove faster than conventional computers at solving the problems facing companies like Google, NASA and aerospace giant Lockheed Martin (which has also purchased a machine).
"What we do is build computers," Rose says, "and if we can build the fastest computers the world has ever known, you can call them whatever you like, and I'll be happy."