Electric switch flips atoms

By Eric Smalley, Technology Research News

Atoms and subatomic particles are like microscopic tops that can spin in one of two directions, up or down. Spintronics and quantum computing use these spin directions to represent the ones and zeros of digital information. Today's electronics, in contrast, use the presence or absence of electric charge to represent binary numbers.

A team of researchers from the Max Planck Institute and the Technical University of Munich in Germany has used an electronic switch to transfer the spin of a group of electrons to the nuclei of atoms in a semiconductor.

Information transfer between electrons and atoms is a key component of spintronics and quantum computing. Atoms in semiconductor crystals are better suited to preserving spin and thereby storing information than electrons because they are fixed in position and they are better insulated from the environment than electrons. Electrons, however, can flow in currents, which makes them better suited to transmitting information.

Computers based on spintronics would be faster, use less electrical power and store data more densely than electronic computers. Data would also remain in memory after the power was turned off, allowing spintronics computers to start instantly.

Quantum computers can use the interactions of individual particles to solve certain problems, like cracking secret codes and searching large databases, that are beyond the abilities of the fastest classical computer possible.

The researchers' experiment proved that it is possible to transfer spin between atoms and electrons, but a lot of work remains before the capability can be put to practical use, said Jurgen Smet, a scientist at the Max Planck Institute. The experiment "brings us one step closer, but we have a large number of giant leaps to go to make something useful and practical," said Smet. "We have succeeded... in a very crude manner for a large ensemble of nuclei, however under extreme conditions, like nearly absolute zero temperature and... a large, stationery magnetic field."

Ordinarily, the spins of electrons and atoms in a semiconductor are isolated from each other. The energy associated with electron spin is considerably greater than the energy associated with atomic spin, and this energy mismatch usually keeps the electrons from changing the atomic spin. But by using a gate, or electronic switch, to control the density of electrons in the semiconductor, the researchers found that at certain densities the interactions between electrons affect the spins of the semiconductor's atoms.

Atomic spins can also be flipped using magnetic fields, which is how hard disk drives in today's computers work. But disk drives are larger, slower and require more energy than the integrated circuits on computer chips. "One would like all-electronic nuclear solid-state devices so that one can marry the benefits of the technology used in present-day electronics with those of quantum computation or spintronics," said Smet.

The researchers' experiment shows that electronic control of atomic spin in semiconductors is possible. However, their technique is unlikely to lead directly to practical technology, said Smet. "The physics we exploit to flip the nuclear spins actually also requires these low temperatures, so there is at least no straightforward rule on how to scale this up," he said.

Still, the research shows that spintronics could be a viable successor to today's electronics. "Atoms... are the smallest unit of which a semiconductor crystal is composed. If you were to extrapolate Moore's Law... you'll find that in the next decade or so we end up with a dimension on the order of the atom," said Smet. Moore's Law, which has held true for the past couple of decades, states that computer speeds double every 18 months as manufacturers shrink computer circuits. "Clearly a paradigm shift has to occur. That is one reason why long-term researchers fervently think about ways to explore the spin degree of freedom of the nucleus of atoms," he said.

Controlling atomic spin could also be used in quantum computing. But to do so, however, the researchers' technique would need to be applied to individual atoms. "This kind of control is not something we will manage to achieve within the next two decades," said Smet.

The researchers device serves as a miniature laboratory for probing the fundamental interactions between electrons and nuclei and exploring the basis for exchanging information between the two spin systems, said David Awschalom, a professor of physics at the University of California at Santa Barbara. "This is a beautiful experiment," he said. "Many people envision that future quantum computing will use nuclear spins for information storage, and thus it is important to explore these basic interactions."

Smet's research colleagues were Rainer Deutschmann, Frank Ertland and Gerhard Abstreiter of the Technical University of Munich, Werner Wegscheider of the Technical University of Munich and the University of Regensburg, and Klaus von Klitzing of the Max Planck Institute. They published their research in the January 17, 2002 issue of the journal Nature. The research was funded by the German Ministry of Science and Education (BMBF) and the German National Science Foundation (DFG).

Timeline:   >20 years
Funding:   Government
TRN Categories:   Materials Science and Engineering; Quantum Computing
Story Type:   News
Related Elements:  Technical paper, "Gate-voltage control of spin interactions between electrons and nuclei in a semiconductor," Nature, January 17, 2002


February 13, 2002

Page One

Tiny wires turn chips inside out

Cooperative robots share the load

Nanotubes take tiny temperatures

Nanotech scheme envisions DNA origami

Electric switch flips atoms


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