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high-performance computing


for example, was once touted as a better replacement. But silicon is abundant and cheap to process. In addition, a silicon crystal has a very stable structure, can be grown to very large diameter boules and processed with very good yields. It is also a fairly good thermal conductor, thus enabling very dense packing of transistors that need to get rid of their heat of operation. Finally, there is a vast amount of production plant already installed and dedicated to making processors out of


QUANTUM ANNEALING SIGNIFICANTLY OUTPERFORMS A CLASSICAL COMPUTER


silicon, yielding huge economies of scale to the silicon industry. ‘For this new technology to become commercially viable, it has to beat the current transistor, the development of which has been given decades and billions – if not trillions – of euros,’ said Mikko.


Quantum computing So, instead of some exotic material such as carbon nanotubes, an alternative path could be radical innovation in silicon technology. In Australia, researchers have created the first two-quantum bit (qubit) logic gate within silicon, which may unlock scalable quantum computers sooner. Principal investigator professor Andrew


Dzurak, based at the University of New South Wales in Australia (UNSW), and his team found that qubits were able to influence each other directly, as a logic gate, when performing calculations using the mechanics of subatomic particles. Like a compass, the magnetic field of


‘The Fridge’ is a closed cycle dilution refrigerator that cools the processor environment to -272°C


$3 billion in chip R&D technologies, which includes carbon nanotubes. Tese are single atomic sheets of carbon rolled up into a tube. Electrons in carbon transistors can move better than in silicon.


Carbon nanotubes Tis October, a team of IBM scientists created a new way to shrink transistor ‘contacts’ of carbon nanotube devices, without reducing performance. Tis was done with a microscopic welding technique that chemically binds metal atoms to the carbon atoms at the ends of nanotubes. With this, contact resistance challenges


www.scientific-computing.com l


could be overcome down to a 1.8 nanometre node. Tis means carbon nanotube-based semiconductors will result in smaller chips with greater performance and lower power consumption. Contacts inside a chip are valves that


control the flow of electrons from metal into the semiconductor’s channels. As transistors shrink, electrical resistance increases within the contacts, impeding performance. Some estimates are that the performance of carbon nanotubes will be five to 10 times better than silicon circuits. But the death of silicon has been predicted many times in the past. Gallium arsenide,


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an electron dictates the binary code of ‘0’ or ‘1’. In a quantum system, particles can exist in two states simultaneously too – a superposition. A two-qubit system can perform simultaneous operations on four values, and a three-qubit system on eight values, etc. Te team morphed their silicon transistors


into quantum bits by ensuring that each one had only one electron associated with it. Ten they stored the binary code on the spin of the electron. ‘Tese two research directions have rather


different strategies,’ said Benjamin Huard a CNRS researcher heading the quantum electronics group at the Ecole Normale Supérieure of Paris, France. Huard, too, is in a position to act as impartial commentator. ‘Te UNSW team… shows that spins in silicon constitute promising candidates.


DECEMBER 2015/JANAURY 2016 15





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