SYDNEY, 3 August 2006 - Researchers from the University of New South Wales, Sydney, have developed a tiny wire that is set to revolutionise the field of quantum electronics.
Known as the 'hole quantum wire', it is about 100 times narrower than a human hair, and is unique in that it does not use electrons to carry an electrical current.
It exploits the gaps, or holes, between electrons instead.
"Research groups around the world have been trying to make these devices for more than a decade," said Alex Hamilton, co-leader of the UNSW Quantum Electronic Devices Group, "and we're the first to do so successfully."
Holes can be thought of as real quantum particles that have, like electrons, an electrical charge and a (magnetic) spin. They exhibit remarkable quantum properties and if utilised may lead to a new world of super-fast, low-powered transistors and powerful quantum computers.
"One difference between holes and electrons is that holes can be thought of as having more spin than electrons," said Hamilton. "If we put an electron inside a region of space with an electric field, the electron's motion is affected but its spin is not. If we do the same thing with holes, our work shows that in a quantum wire the electric field affects both the motion and the spin."
Controlling spin is considered vital in the development of new high-speed electronics applications, known as spintronics, where semiconductor devices have both electric and magnetic properties.
Today's microchips use only the charge properties of electrons. And quantum wires developed to date, though so narrow that electrons must pass along them in single file, have only made it possible to exercise limited control over an electron's spin.
The spin of a quantum hole, however, can be strongly affected by electric impulses.
Working with researchers in Britain, Japan and New Zealand, the team created a super-clean gallium arsenide quantum wire that could use holes to carry a current.
"Until now it has not been possible to make high-quality hole nanostructures," Hamilton said. "What we've done is to make highly stable hole quantum wires, where the holes can travel without hitting anything else."
"As the holes pass along the wire, they line up like soldiers marching in single file … their magnetic dipoles (imagine little bar magnets) all want to point along the wire. Electrons don't do this.
"This means that we can manipulate the spin properties of the holes by forcing them into these narrow quantum wires, which is one of the pre-conditions for making spin-based transistors."
The findings will be presented at the 26th international conference on the Physics of Semiconductors, in Vienna, Austria.
