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When it comes to energy efficiency, today’s computers eat up some eight orders of magnitude more than the theoretical minimum. Clearly, there’s room for improvement.

Today, Quentin Herr and pals at Northrop Grumman Systems in Baltimore reveal a superconducting logic device that uses 300 times less power than conventional silicon chips. That’ll be a shock to chip-makers whose attempts at energy efficiency improvements pale in comparison.

The laws of physics help, of course. The power dissipated by a conventional transistor depends on its size and on the material from which it is made.

By comparison, the energy dissipated by the superconducting equivalent, the Josephson junction, is determined only by thermal noise, the system being entirely free of the troublesome resistance that eats up energy in conventional devices.

To exploit this, Herr and co developed and built a new type of device known as a reciprocal quantum logic chip. Their superconducting chip is made of niobium, operates at 4.2 kelvin and consists of 1600 Josephson junctions .

They say it can operate at clock speeds of 6 Ghz with a 6 mW power supply, that faster speeds are possible and that this performance can scale to chips with a million junctions. And it does it with a bit error rate of less than 10^-40. That’s practically nothing.

But the jaw dropper is the power consumption which is only three orders of magnitude above the theoretical limit.

That isn’t the wall plug power consumption, of course, since the hefty cost of cooling has to be taken into account. But even when it is, Herr and co say the new device outperforms silicon power consumption by a factor of 300.

That makes superconducting logic a tempting option for high end computing, for which energy bills are a considerable cost. In 2007, US Environmental Protection Agency calculated that servers and data centres in the US eat up some 12 GW of power, equivalent to the output of 25 power plants. Cutting that by a factor of 300 would save a few dollars.

Niobium also offers an interesting extra. It is naturally radiation hard meaning that these chips might be particularly well suited to operating in space or other highly radioactive environments. That’s the kind of thing that can help to generate military funding. Indeed, Herr and co’s work was funded in part by the Defense MicroElectronics Activity, a military research organisation based in Sacramento.

Interestingly, the device might also be easily converted to work in the quantum computing regime, simply by cooling it down to a few millikevin. That could make it a useful stepping stone towards quantum technologies.

That this technology has come out of Northrop is something of a surprise. This is a company that makes the Global Hawk UAV and the B-2 bomber along with many other military technologies. However, Herr’s work suddenly makes it a player in the world of next generation computing. It’ll be interesting to see where this goes
Ref: arxiv.org/abs/1103.4269: Ultra-Low-Power Superconductor Logic

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