Courtesy of D-Wave Systems Inc
high-performance computing
process called quantum annealing to exploit quantum mechanical effects, such as tunnelling and entanglement. In December, research by the team at Nasa Ames showed that quantum annealing significantly outperformed a classical computer for problems involving nearly 1,000 variables. Te team thinks it’s found a quantum algorithm that solves certain problems 100 million times faster than conventional processes on a PC. Despite this progress, doubts remain. ‘I do
not rule out a quantum-annealing design, but it is not clear if such a technology will really scale in the way it needs to, in order to overtake conventional processors,’ said Dzurak. Although technically impressive, the
Part a of a D-Wave processor being constructed ➤
Comparatively, the IBM discovery is more incremental, since it can readily be applied to usual computers if the technology is pushed to its limits.’
Time for development However, it may take at least a decade before a commercial qubit chip could be ready, even if all goes well. ‘We are aiming to have a prototype chip that demonstrates the manufacturing pathway ready in five years. I think it will be very challenging to have a commercially available processor chip ready within 10 years,’ said Dzurak. Te Australian team has just patented its design for a full- scale quantum computer chip of millions of qubits. Te engineering programme to scale this technology from chip to a supercomputer-scale system has just begun. ‘If we could do it in less than 15 years, I’d be a very happy man. I think most experts in the field would agree with my assessment,’ said Dzurak. Back in 1998, researcher Bruce Kane first
proposed the idea of silicon-based quantum computer in a Nature paper. In theory, a quantum computer with just 300 quantum qubits could hold 2 to the power of 300 values simultaneously – which is around the number of atoms in the known universe – performing an incredible quantity of calculations at once. In reality, qubits are prone to errors; you
need lots of extra bits or ‘ancilla’ bits, which have a secondary error-correction role in a logic circuit. Te actual number of physical qubits for equivalent and, most importantly, accurate computational power could add up to millions when scaled up to silicon semiconductor technology. IBM scientists recently made a new type of
16 SCIENTIFIC COMPUTING WORLD IT WILL BE
CHALLENGING TO HAVE A PROCESSOR CHIP READY WITHIN 10 YEARS
chip that for the first time was able to detect and measure both kinds of quantum errors – bit-flip and phase-flip – simultaneously. ‘Tere are other qubits in the lattice that
serve as the data or code qubits, and hold the quantum information. Tese data or code qubits get checked by the ancillas,’ said Jerry Chow, manager of IBM Research’s Experimental Quantum Computing Group. Quantum decoherence are errors in
calculations caused by interference from many factors. Tese errors are especially acute in quantum machines. ‘We do believe we have a promising path
forward for scalability... Systems of 50-100 qubits we expect to be possible within the next five years,’ said Chow.
Commercial quantum computers To date, the Canada-based D-Wave system is the only commercially available quantum computer of its type on the market. In 2011 a D-Wave quantum computer was sold to the company Lockheed Martin, and in 2013 a 500-qubit D-Wave Two system was installed at Nasa Ames, where researchers from Google, Nasa, and the Universities Space Research Association (USRA) have been using it to explore the potential for quantum computing. Tis year, the US Los Alamos National Laboratory purchased one. Te computer’s processors use a particular
D-Wave is not faster than classical computers. ‘It is not clear if the current D-Wave computers are truly quantum computers. Tere is no evidence that they are faster than classical computers,’ said Dr Menno Veldhorst, a UNSW research fellow and lead author of the two-qubit paper. Future developments include chips
directly interfacing with other components using light, rather than electrical signals. ‘One problem with photon-based quantum computers (QCs) is that there are a lot of overheads to make the chip function,’ said Dzurak. ‘I wouldn’t rule it out. Tere is a lot of interesting work on photonic-based QCs. If I had to place a bet, I would say the first commercial system will either be a silicon- based QC or a superconductor-based QC.’
Quantum dots Veldhorst also thinks large-scale architectures will likely come from silicon-based quantum- dot qubits and superconducting qubits – something Professor John Martinis’ research group at the University of California Santa Barbara and Google is currently working on. A quantum dot breakthrough was recently
achieved by a team of physicists at the Technical University of Munich, Germany, and the Los Alamos National Laboratory and Stanford University in the US. Tey produced a system of a single electron trapped in a semiconductor nanostructure, with the electron’s spin used as the data carrier. Te team found data-loss problems caused
by strains in the semiconductor material, but these were solved when an external magnetic field with the strength of a strong permanent magnet was applied. Tis system of quantum dots (nanometre-scale hills) was made of semiconductor materials that are compatible with standard manufacturing processes. ‘A large-scale quantum computer will take another decade or two,’ said Veldhorst. l
@scwmagazine l
www.scientific-computing.com
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