Quantum computer bests all conventional computers in first claim of 'supremacy'.

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Google researchers in Santa Barbara say their advance may lead to near-term applications of quantum computers. iStock.com/JHVEPhoto
▼ The age of quantum computing may have begun not with a flashy press conference but with an internet leak. According to a paper posted briefly--and presumably mistakenly--to a lab site, physicists at Google have used a quantum computer to perform a calculation that would overwhelm the world's best conventional supercomputer. Although the specific computation has no known use, the result means that scientists have passed a milestone known as "quantum supremacy."
"It's a great scientific achievement," says Chad Rigetti, a physicist and founder and CEO of Rigetti Computing in San Francisco, which is developing its own quantum computers. "Google called their shot," he adds, noting that the company detailed exactly how it would demonstrate quantum supremacy a couple years ago. Greg Kuperberg, a mathematician at the University of California, Davis, calls the advance "a big step toward kicking away any plausible argument that making a quantum computer is impossible."
According to theFinancial Times, which broke the story, the paper appeared last week on the web site of NASA's Ames Research Center in Moffett Field, California, some of whose researchers are authors on it. Readers downloaded the manuscript before it vanished, and it is circulating on the web. John Martinis, the physicist who leads Google's quantum-computing effort in Santa Barbara, California, declined to comment on the paper, but others in the field think it is legitimate.
A quantum computer aims to exploit the strange aspects of quantum mechanics to perform types of calculations that would swamp a classical computer. Whereas a classical computer depends on "bits" of information that can be set as either zero or one, a quantum computer employs qubits which can be set to zero, one, or--thanks to quantum mechanics--any combination of zero and one at the same time. That enables a quantum computer to process a multitude of inputs simultaneously. For example, a 10-qubit quantum computer could process 210, or 1024, possible inputs at once instead of analyzing them one at a time.
But such a computer's real power comes from other quantum phenomena. For certain computational problems, all potential solutions can be thought of as quantum waves simultaneously sloshing among the qubits. Set things up right and those waves will interfere with one another so that incorrect answers cancel one another and the right answer pops out. Such interference should enable a full-fledged quantum computer to hack current internet encryption schemes by factoring the huge numbers that underlie them (Science, 23 August, p. 730.).
That feat would require thousands of (▪ ▪ ▪)

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