D-Wave’s machine is intended to do one thing better than a conventional computer: finding approximate answers to problems that can only be truly solved by exhaustively trying every possible solution. D-Wave runs a single algorithm, dubbed quantum annealing, which is hard-wired into the machine’s physical design, says Geordie Rose, D-Wave’s founder and CTO. Data sent to the chip is translated into qubit values and settings for the couplers that connect them. After that, the interlinked qubits go through a series of quantum mechanical changes that result in the solution emerging. “You stuff the problem into the hardware and it acts as a physical proxy for what you’re trying to solve,” says Rose. “All physical systems want to sink to the lowest energy level, with the most entropy,” he explains, “and ours sinks to a state that represents the solution.”
“You stuff the problem into the hardware and it acts as a physical proxy for what you’re trying to solve,” says Rose.
Although exotic, this hardware is intended to be used by software engineers who know nothing of quantum mechanics. A set of straightforward protocols—dubbed APIs for application programming interface—make it easy to push data to the D-Wave system in a standard format.
“You send in your problem and then get back a much more accurate result than you would on a conventional computer,” says Rose. He says tests have shown software using the D-Wave system can learn things like how to recognize particular objects in photos up to 9 percent more accurately than a conventional alternative. Rose predicts that the gap will rapidly widen as programmers learn to optimize their code for the way D-Wave’s technology behaves.
Google has been experimenting with D-Wave’s technology for several years as a way to speed up software that can interpret photos. The company’s software engineers use it as a kind of cloud service, accessing a system at D-Wave’s Vancouver headquarters over the Internet. In 2009, the company published papers showing that using the quantum system outperformed conventional software running in a Google data center.
Allan Snavelly at San Diego Supercomputer Center has used conventional versions of the algorithms like those that are built into D-Wave’s system. He says that the kind of “needle in a haystack” problems they are designed for are important in computer science. “These are problems where you know the right answer when you see it, but finding it among all the exponential space of possibilities is difficult,” he says. Being able to experiment with the new system using conventional software tools will be tempting to programmers, says Snavelly. “It’s intriguing to consider the possibilities—I would like to get my hands on one.”
D-Wave’s technology has been dogged by controversy during the 12 years it has been in development, with quantum computing researchers questioning whether the company’s technology truly is exploiting quantum effects. A paper published in the science journal Nature on May 12 went some way to addressing those concerns, reporting that the behavior of one of the eight-qubit tiles that make up the D-Wave One is better explained by a mathematical model assuming quantum effects at work than by one assuming only classical physics was involved.
However, the experiment did not show the results of running a computation on the hardware, leaving doubt in the minds of many quantum computing experts. Rose says the technology definitely uses quantum effects, but that to programmers only one thing really matters. “Compared to the conventional ways, you get a piece of software that is much better.”