Date:14/03/16

Experiment shows magnetic chips could dramatically increase computing's energy efficiency

In a breakthrough for energy-efficient computing, researchers have shown for the first time that magnetic chips can operate with the lowest fundamental level of energy dissipation possible under the laws of thermodynamics.

The findings mean that dramatic reductions in power consumption are possible - as much as one-millionth the amount of energy per operation used by transistors in modern computers, researchers said.
This is critical for mobile devices, which demand powerful processors that can run for a day or more on small, lightweight batteries, they said.

"We wanted to know how small we could shrink the amount of energy needed for computing. The biggest challenge in designing computers and, in fact, all our electronics today is reducing their energy consumption," said Jeffrey Bokor from University of California, Berkeley in the US.

Lowering energy use is a relatively recent shift in focus in chip manufacturing after decades of emphasis on packing greater numbers of increasingly tiny and faster transistors onto chips, researchers said.
"Making transistors go faster was requiring too much energy. The chips were getting so hot they would just melt,” said Bokor.

Researchers have been turning to alternatives to conventional transistors, which currently rely upon the movement of electrons to switch between 0s and 1s. Partly because of electrical resistance, it takes a fair amount of energy to ensure that the signal between the two states is clear and reliably distinguishable, and this result in excess heat.

Magnetic computing emerged as a promising candidate because the magnetic bits can be differentiated by direction, and it takes just as much energy to get the magnet to point left as it does to point right, researchers said.

"These are two equal energy states, so we do not throw energy away creating a high and low energy," said Bokor.

They experimentally tested and confirmed the Landauer limit, named after IBM Research Lab's Rolf Landauer, who in1961 found that in any computer, each single bit operation must expend an absolute minimum amount of energy.

Landauer's discovery is based on the second law of thermodynamics, which states that as any physical system is transformed, going from a state of higher concentration to lower concentration, it gets increasingly disordered. That loss of order is called entropy, and it comes off as waste heat.

Researchers used a laser probe to carefully follow the direction that the magnet was pointing as an external magnetic field was used to rotate the magnet from "up" to "down" or vice versa.

They determined that it only took 15 mill electron volts of energy - the equivalent of 3 zeptojoules - to flip a magnetic bit at room temperature, effectively demonstrating the Landauer limit.

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