A quantum wire is a cable or a wire, often similar in function to copper wire, but made with nanotubes of a specific element, usually carbon. Quantum wires are usually conductors, but may also be made as insulators or semiconductors. These wires are ideal for electrical wiring functions and for use on spacecrafts because they are smaller and lighter than their metal counterparts. They are, however, expensive to produce.
Nanotubes are man-made microscopic tubes with a diameter of 1 nanometer, which measures 1 billionth of a meter. In comparison, the diameter of a single human hair is measured in micrometers, which are 1,000 times larger than a nanometer. Nanotubes are not only used to create quantum wire, but are used in a variety of scientific fields, including medical research.
Discovered in 1991, nanotubes are made when a laser is shot at a pure substance, such as carbon. Originally this was a lengthy process with many potential nanotubes discarded because they did not fit the size requirements, but Rice University researchers had perfected a process for making appropriately sized nanotubes by 1996.
Nanotubes must be linked or twisted together in chains to form quantum wires, which have a higher conductivity than copper wires, the best metallic conductor of electricity. In theory, a quantum wire has one-sixth of the weight of a copper wire and can conduct electricity up to ten times more efficiently. Metallic quantum wires may be made out of nickel (Ni) or gold (Au). These wires are largely still experimental, but have uses in electronics and optics.
Possibly the most scientifically exciting type of quantum wire, however, are ones made from carbon nanotubes. In 2005, Rice University was conducting extensive research into making quantum wire from carbon nanotubes, using a grant of $11 million US Dollars (USD) from the United States' National Aeronautics and Space Administration (NASA). Slated to be completed in 2010, Rice University was charged with the task of creating quantum wire long enough to be used in spacecrafts.
Since the wires are lighter and more efficient, NASA and other scientists, believe that quantum wires could be instrumental in allowing spacecrafts to travel farther into space since every extra pound costs a spacecraft more fuel. Scientists have problems producing enough nanotubes to make long lengths of wire, however, since a very specific nanotube shape, called "arm chair," is necessary to twist them into wires. In 2005, only two percent of nanotubes had the correct shape for use. As of 2010, however, Rice University researchers had made considerable progress in solving the problem, but more research was still needed.