"Spin" doctors

A small perpendicular magnetic field bends a beam of holes in a gallium arsenide semiconductor along two different cyclotron trajectories, the radius depending on the spin of the particles. Those holes with up spin curve in one direction and those with down spin in the other. The light-colored lines are oxide, which separate different regions of 2D hole gas beneath the surface.

A small perpendicular magnetic field bends a beam of holes in a gallium arsenide semiconductor along two different cyclotron trajectories, the radius depending on the spin of the particles. Those holes with up spin curve in one direction and those with down spin in the other. The light-colored lines are oxide, which separate different regions of 2D hole gas beneath the surface.


A device that splits a single stream of electrons or electron holes into two according to their up or down spin could form a key component in quantum computers, say physicists at Purdue University. Unlike conventional computers that run jobs stepwise, quantum computers could simultaneously perform multiple steps, significantly boosting computer power.

Making this possible is a quantum-physical property called entanglement. For example, a pair of entangled electrons form a quantum bit that at once is both on and off, or in the parlance of digital computers, a 1 and 0. But only after the pair is separated can useful information be extracted.

In the laboratory, the team used highly purified gallium arsenide sandwiched between layers of aluminum gallium arsenide to push holes into two different directions according to their spin state. Holes are the spaces left behind by electrons traveling through a semiconductor, and separating them according to their spin has been a challenge, one that the Purdue technique addresses.

But don't expect to see quantum computers on the shelf any time soon. The technique (so far) works only at temperatures a fraction of a degree above absolute zero and will have to be reproduced at much higher temperatures for use in practical devices. Funding for the research comes from Darpa and the National Science Foundation.