Puddle that spins together stays together.

In conventional electronics, typified by semiconductor devices, charge rules. Circuits sense, direct, store, and process electrons as units of electric charge. In the infant field of spin electronics, or "spintronics," however, a different electron property, known as spin, serves as the coin of the realm.

Researchers have harnessed spin in metals already--for instance, in the circuits used in computers' hard magnetic disk drives. For semiconductors, however, scientists are still exploring rudimentary manipulations of electron spin, which physicists describe as analogous to the rotation of a particle about an axis. Development of a spin-based semiconductor could hasten the advent of extraordinarily compact, speedy computer memory and other circuits. The devices would combine advantages of spintronics with the low-cost mass production typical of semiconductor circuits.

In the Jan. 14 NATURE, James M. Kikkawa and David D. Awschalom of the University of California, Santa Barbara report experimental evidence hinting at practical control of electron spin in semiconductors.

The researchers used electric fields to propel "puddles" of electrons within ultracold strips of gallium arsenide. First, they used a laser pulse to induce the millions of electrons in the sample to orient their spins alike. The experimenters found that they could move this puddle more than 100 micrometers--a distance hundreds of times greater than the spacing between components in an integrated circuit--before the spin coordination broke down.

"This experiment shows that the spin puddles can move without significantly increasing the loss of quantum information to outside of the electronic system," Kikkawa says.

One potential use of spintronics is in quantum computers (SN: 9/12/98, p. 165). Although extremely rudimentary today, such devices may eventually outdo conventional computers by exploiting the quantum-mechanical nature of matter.

The new result suggests that scientists may yet find a way to shuttle fragile data around inside a quantum computer without loss or damage, says Bruce E. Kane of the University of New South Wales in Sydney, Australia. "Maybe the physics is going to allow us to do that. It's a very interesting result."

The physics itself may have to stretch. Theories of electron spin flow seem unable to fully explain the surprising distance the puddles go. "The data suggest there's new semiconductor physics here that people may have missed," Awschalom says.

The fragility of quantum data arises because the spin orientation of a quantum-mechanical entity, such as an electron, can be represented as a complex set of probabilities of different spin directions. This complexity collapses to a single state--with loss of valuable data--if the electron's spin is measured or in other ways interacts with the environment.

The authors stress that the experiment stopped short of proving that the spin characteristics of the individual puddle electrons remained fully intact. Although not affected by outside forces, the electrons themselves may have interacted to cause collapses.