“So any way to speed this up with a protocol that can deal with errors simultaneously is likely to be a significant improvement,” said Steve Rolston, the co-director of the Joint Quantum Institute at the University of Maryland. “Almost all of the qubits in a real quantum computer are going to be there for error detection. It seems kind of crazy but it could be the case that 99 percent of the qubits that are there in a quantum computer are there for error detection and correction.”

The race to build a large-scale working quantum computer has intensified in recent years—and recent months, in particular. In 2013, Google bought what it says is a quantum computer from the company D-Wave, a Canadian company which has also sold its machine to the defense contractor Lockheed Martin. (Google is also letting NASA use the D-Wave system as part of a public-private partnership.) In March of this year, Google said it had built a nine-qubit device that successfully detected one (but not both) of the key kinds of errors typical in quantum computing. After IBM's announcement that followed in April, D-Wave announced in June it had broken the 1,000-qubit barrier, a processing milestone that it said would allow “significantly more complex computational problems to be solved than was possible on any previous quantum computer.”

D-Wave has a somewhat controversial history, with critics saying its claims about what its computers can do are often overstated. And yet there's no question that much has happened in the two decades since Shor's algorithm, named for the mathemetician Peter Shor, first offered a framework for quantum computing. “Peter shor came up with his algorithm in 1994,” Rolston told me. “It's been a long time now, a surprisingly long time in some ways. If you look at what's really happened in those last 20 years, mainly what people have been doing is really trying to perfect qubits and interactions with one or a handful of qubits—keeping the idea of scability in the back of their minds. There's no pont in me making a perfect qubit if I can't make hundreds, but there's also no point in desinging a hundred if I can't get one or two to behave properly.”

Up until about five years ago, most quantum computing work was still being done on single-qubit level. That's rapidly changing. “The real challenge,” Chow, of IBM, said, “is how we're going to controllably put more and more of these together so we can still control what we need to but the quantum information can be protected. People say we're basically somewhere between the vacuum tube and transistor. We're still in the early days.”

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