Mar 05, 2014 |
Seeking quantum-ness: D-Wave chip passes rigorous tests
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(Nanowerk News) With cutting-edge technology, sometimes the first step scientists face is just making sure it actually works as intended.
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The USC Viterbi School of Engineering is home to the USC-Lockheed Martin Quantum Computing Center (QCC), a super-cooled, magnetically shielded facility specially built to house the first commercially available quantum computing processors – devices so advanced that there are only two in use outside the Canadian lab where they were built: The first one went to USC and Lockheed Martin, and the second to NASA and Google.
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Since USC's facility opened in October 2011, a key task for researchers has been to determine whether D-Wave processors operate as hoped – using the special laws of quantum mechanics to offer potentially higher-speed processing, instead of operating in a classical, traditional way.
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An international collaboration of scientists has now published several papers rejecting classical models of the first-generation D-Wave One processor housed at USC, including one on an elaborate test of all 108 of the chip's functional quantum bits ("qubits"). The test demonstrates that the D-Wave One behaved in a way that agrees with a model called "quantum Monte Carlo," yet disagreed with two candidate classical models that could have described the processor in the absence of quantum effects.
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The research was published on Feb. 28 by Nature Physics ("Evidence for quantum annealing with more than one hundred qubits").
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"The challenge is that the tests we can perform on the USC-based D-Wave processor can't directly 'prove' that the D-Wave processor is quantum – we can only disprove candidate classical models one at a time," said QCC Director Prof. Daniel Lidar. "But so far we find that the D-Wave processor is always consistent with our quantum models. Our tests continually get more rigorous and complex."
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Add this to recent work involving USC Information Sciences Institute researcher Federico Spedalieri demonstrating entanglement in a chip at the company's headquarters in Burnaby BC as well as previous testing of a smaller group of qubits by Spedalieri, Lidar and their collaborators, and the evidence is mounting that quantum effects are at play in the D-Wave processors.
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Quantum processors encode data in qubits, which have the capability of representing the two digits of one and zero at the same time – as opposed to traditional bits, which can encode distinctly either a one or a zero. This property, called superposition, along with the ability of quantum states to "interfere" (cancel or reinforce each other like waves in a pond) and "tunnel" through energy barriers, is what may one day allow quantum processors ultimately perform optimization calculations much faster than traditional processors.
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Optimization problems can take many forms, and quantum processors have been theorized to be useful for a variety of big data problems like stock portfolio optimization, image recognition and classification, and detecting anomalies, such as rooting out bugs in complex software.
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The first quantum chip housed at the QCC was a 128-qubit D-Wave One, which was replaced about a year ago with the 512-qubit D-Wave Two. Though every chip is unique, the repeated validation of the older chip bodes well for its successor, which shares the same architecture.
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"Our work is part of a large scale effort by the research community aimed at validating the potential of quantum information processing, which we all hope might one day surpass its classical counterparts," Lidar said.
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