Monday, October 25, 2004

"QUANTUM: 'Spin filter' initializes quantum computing"
Purdue University researchers have invented a "spin filter" that can sort charge carriers by their spin state. "This component is essential to future quantum computers, which need to be initialized in a known state," said professor Leonid Rokhinson. "It will also be necessary for the many other 'spintronic' devices that people are working on today." Storing data on the polarized-wave function, or "spin," of a charge carrier- a mobile electron or hole in a semiconductor-holds promise for future single-electron transistors, nanoscale nonvolatile memories, quantum computers and other so-called spintronic devices. But even the simplest components necessary to make spintronics a reality-such as filters-have been lacking. Using the basic physics of a mass spectrometer as his model, Rokhinson fabricated a chip version that can sort particles based on their spin configuration. "Spin filters are one of the most crucial missing ingredients of spintronic devices because they allow you to create spin polarization," he said. The device uses magnetic focusing to enable the spatial separation of trajectories of carriers (in a two-dimensional "hole" gas fabricated from GaAs heterostructures) by virtue of their spin state. Two quantum-point contacts, acting as a monochromatic source of ballistic holes and a narrow detector, respectively, were demonstrated to work as a tunable spin filter.