If handling electrons is like a basketball game, then scientists just improved their dribbling skills. They can now manipulate a line of current only a few electrons wide as it hovers over a channel of liquid helium. The advance brings researchers a step closer to the Michael Jordan-like moves necessary to build the first quantum computer.
In 1934, physicist Eugene Wigner proposed that at low temperature, electrons would crystallize, their negative charges keeping them evenly spaced. It took about 60 years to make a "Wigner crystal" and to realize that it could be the foundation of a quantum computer. Such a machine, still largely a fantasy, would store bits of information as single electrons and make calculations that would take billions of years with today's fastest number crunchers.
Now, Michael Lea and colleagues from the University of London have created a "Wigner wire," the smallest packet of electrons anyone has managed to isolate and control. To hold the electrons, team members at the Niels Bohr Institute in Copenhagen cut micron-sized channels in a semiconductor wafer. Then they filled the channels with helium cooled to less than 1 degree above absolute zero. Electrodes above and below the chip kept electrons in the channel. To detect the electrons and show that they had crystallized, Lea's group applied a current to the channel. When the current reached a critical level, resistance shot up, the researchers describe in the 22 October issue of Physical Review Letters. This indicates waves in the helium stirred up by electron flow, and it can only happen when electrons are organized into crystals.
"It's a huge breakthrough," says Mark Dykman of Michigan State University in East Lansing, one of the physicists who first proposed building a quantum computer with Wigner crystals and helium. The study shows it's possible to manipulate a crystal just a few dozen electrons wide, whereas previous studies grappled with thousands. But quantum computers must wait until scientists fabricate a smaller electron receptacle, submerge it in helium, and then deliver and control a single electron, Dykman says. "All the pieces are in place," he states. "What is important is to learn how to bring them together."