Four atom-wide wire may herald tiny computers

A wire that is just four-atoms wide and one-atom tall, yet works just as well as the ordinary copper wires running behind your wall, was recently created by an international team of scientists. 

The breakthrough brings closer to reality a future where computers  smaller than a pinhead are faster and more powerful than some of today's supercomputers, according to the researchers.

Such so-called quantum computers will require wires to get information in and out of the quantum bits, or qubits, that perform calculations, explained Gerhard Klimeck,  an electrical and chemical engineer at Purdue University in West Lafayette, Ind.

"These wires are our approach to how we might drive quantum computing bits," he told me Tuesday.

Dirt in silicon
The wires, which are 10,000 times thinner than a human hair, were made by placing chains of phosphorus atoms within a silicon crystal.

Phosphorus is essentially "dirt" that adds electrons to silicon, Klimeck explained.

"What's novel here is that we can put so many phosphor impurities together and close that they have an effect of making a metal-like conductor inside silicon … which is like an insulator around the wire," he said.

The research was led by Bent Weber, a graduate student in quantum computing at the University of New South Wales in Australia and was described in the Jan. 5 issue of Science. 

Testing laws
The finding proves that Ohm's law, which demonstrates the relationship between electrical current, resistance, and voltage, applies all the way down to the atomic scale.

Some researchers believed the law would break down at the microscopic scale where quantum mechanics would drive the behavior of electron motion,  David Ferry,  a computer and electrical engineer at Arizona State University, explains in an accompany perspective article in Science.

The finding that "Ohm's law remains valid, even at very low temperatures is a surprising result that reveals classical behavior in the quantum regime," he writes.

While this may jigger how scientists sort quantum effects from classical ones, he adds, it comes as good news to the semiconductor industry which seeks to extend Moore's Law down to the atomic scale.

This is the law that says the number of transistors squeezed onto an integrated circuit at least doubles every two years.

"It has been thought that quantum effects would limit this in the near future," writes Ferry, "but the results presented by Weber et. al suggest that several generations are still possible."

Tiny computers
This atomic-scale wire, noted Klimeck, will allow computer chip manufacturers to connect traditional or novel transistors at the atomic scale. 

"Architecturally, it may not look very different than today's Intel chip, in terms of how that thing actually works," he said.

Different-looking chips will come with advances in quantum computing, where individual atoms inside a piece of silicon may perform computations in the way that linked transistors do in today's computers.

The atomic-scale wires will get information in and out of these quantum bits.

Both concepts of tiny computers, though, won't get any smaller than the atomic scale, Klimeck added. "You have to have atomic wires that get down to the atomic scale to get the information in and out." 

The wire they created "is the end of Moore's Law," he said. "You are not going to make a wire smaller than that." 

Not yet for sale
Consumers eager to get their hands on these teeny tiny computers will have to wait awhile, noted Klimeck. 

The lab manufacturing process involves using a scanning tunneling microscope to carve a pattern into the surface of silicon one atom at a time, which is much too slow for industrial scale production.

"While we demonstrated that you can make these wires, and that they function, we have not demonstrated a scalable way of how to mass produce them," he said.

This will likely eventually be figured out by an innovator in the multi-billion computer technology industry racing to keep up with Moore's Law.