A speed test between quantum and classical computers has ended in a draw. New research suggests the commercial quantum computer sold by Canadian company D-Wave Systems isn’t faster than the PC on your desk.

In theory a quantum computer, which uses the quirks of quantum mechanics to perform calculations, should leave today’s most powerful machines in the algorithmic dust. A classical computer encodes data as familiar zeros and ones, known as bits. A quantum computer, on the other hand, uses subatomic particles known as qubits that can be zero, one, or a simultaneous superposition of the two. This should technically allow a quantum computer to test a huge number of possibilities at the same time. Just how much faster a quantum computer is able to run through a problem than a classical computer is known as “quantum speedup.”

Since 2011, D-Wave has been selling a commercial product that uses a particular architecture known as adiabatic quantum computing to perform calculations. So far, many researchers are skeptical of just how much of an advantage the product gives over other computers. But earlier this year, a team at Google and NASA raced one of D-Wave’s machines against several off-the-shelf algorithms and found that the quantum product was about 35,500 times quicker than the classical solvers.

Not so fast. Google’s test wasn’t exactly a one-to-one comparison because the off-the-shelf products were not optimized to solve these particular problems. Another team has also been testing D-Wave’s machine against regular old computers, running optimization algorithms on both that fairly matched their abilities.

“We found no evidence of quantum speedup,” said physicist Matthias Troyer of the Swiss Federal Institute of Technology in Zurich, Switzerland, co-author of a paper that appeared today in Science. “When we looked at all problems, the machine worked the same as a classical computer.”

The heart of NASA’s D-Wave computer. NASA Ames / John Hardman

Though the team found some instances where the D-Wave machine could solve five times faster than an ordinary PC, they also discovered certain problems where the quantum computer was about 100 times slower. Troyer said that it was impressive that D-Wave’s brand new technology was able to keep up with modern computer chips, which have been honed over many decades of research. But its quantum speedup abilities remain unproven.

“It’s a solid piece of research that puts a big question mark on whether or not the D-Wave approach will give us a tremendous speedup,” said computer scientist Wim van Dam from the University of California, Santa Barbara, who was not involved with the work.

So is that the end of D-Wave’s speedy powers? Not yet. Quantum speedup effects could still show up in other types of algorithms run on D-Wave’s machine. The company thinks that the classes of algorithms that Troyer and his team used went too easy on the classical computers.

“This particular result in Science isn’t that significant,” said computer scientist Colin Williams, D-Wave's director of business development. “They need to pick problems that are much harder.”

Williams pointed to another researcher, computer scientist Itay Hen of the University of Southern California, who has done more recent work that seems to show particular specialized problems where the D-Wave machine computed faster than a classical computer. Hen presented some of his results last week at the Third Workshop in Adiabatic Quantum Computing in Los Angeles. But he says his work is still fairly preliminary.

Thomas Porostocky

“I would say the D-Wave guys are, at least for now, too optimistic,” Hen said.

D-Wave is still banking on other research that might vindicate their machine. The Google/NASA team has yet to publish their full results, which Williams said could appear in the not too distant future.

For now, researchers will continue to search for classes of problems that show a quantum speedup on D-Wave’s machine. Troyer said that no experiment could ever rule out the existence of such problems, but it remains to be seen if they will only be specially tailored instances or if they could have real-world applications. D-Wave’s architecture is particularly suited to optimization problems, such as finding the quickest route between a set of points. If it showed an advantage over classical techniques, it might be a boon to businesses that need such information, such as airlines, delivery companies, or those making mapping software.