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Aaronson’s surly tone was typical. Umesh Vazirani, a professor of computer science at the University of California, Berkeley, said, “D-Wave is misleading the public by calling their device ‘a practical quantum computer.’ The whole point of quantum computing is achieving a large speedup over classical computers, something that D-Wave hasn’t accomplished.”

Something solved the problems at the demonstration, but it might not necessarily be a quantum computer. In particular, computer scientists do not know how well the Orion corrects for the crescendo of errors, caused by thermal noise and the decoherence of qubits, that is attendant upon any quantum computation. These errors must be carefully managed if a quantum computer is to work. Indeed, according to all the computer scientists to whom Technology Review spoke, because the Orion can function as a rather slow analog computer, it’s possible that the Orion was not really performing quantum operations at all when it was demonstrated at the Computer History Museum.

“Has D-Wave really implemented a 16-qubit quantum computer, or do their qubits decohere so quickly that they are in effect implementing a classical algorithm?” asked Vazirani. “D-Wave has not provided any evidence to favor the first possibility over the second.”

The most generous quantum computing scientists will grant that D-Wave has made an interesting gamble.

“I don’t know much about business, but I imagine that the reasoning at D-Wave is something like the following,” said Seth Lloyd, a professor of mechanical engineering at MIT, who proposed the first technologically feasible design for a quantum computer. “Say the odds are 10-to-1 against adiabatic quantum computing working, so the venture is likely to fail. But if it succeeds, then they’ll clean up. What D-Wave is doing is unlikely to succeed, but it is not quixotic.”

We asked Geordie Rose to defend the Orion to his critics.

Jason Pontin: Did you, in fact, demonstrate the world’s first practical quantum computer?

Geordie Rose: Yes.

JP: Well, that’s blunt. Is a truly fault-tolerant, adiabatic computer a quantum computer?

GR: Yes.

JP: That begs this question, I’m afraid: is the Orion fault-tolerant?

GR: Yes, it is.

JP: Really?

GR: If you’d like me to elaborate, I can.

JP: That would be nice.

GR: There are two different concepts here. Fault tolerance is first and foremost about whether the processor will continue to function as it was designed in the presence of faults. In the system that we operated during the demo, the chip had 2 broken components out of 56, and the thing operated beautifully in the presence of those faults. So the Orion is absolutely fault-tolerant. There’s no question. We’ve demonstrated that. But I think you’re really asking about decoherence.

JP: I am.

GR: The presence of noise in a quantum computer can cause errors. If you want to run a quantum computer coherently, to be able to do anything that a quantum computer possibly can do, you need to actively remove errors. In our approach, the adiabatic model, the physics of the device is quite different from conventional quantum computers like gate models. In order for an error to happen at all in our approach, you need to supply a certain amount of energy which physicists call an “energy gap.” If the noise doesn’t have at least that amount of energy, it can’t do anything bad. So if you don’t supply that amount of energy, there’s a natural gap that protects the system from noise. Adiabatic quantum computers are known to be much more robust to noise than other approaches.

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Credit: Copyright 2007 D-Wave Systems Inc., J. Chung and M. Thom

Tagged: Computing, venture capital, Q&A, computation

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