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Yale research team develops
the world's fastest single-electron transistor

Scientists at Yale have developed the world's best electrometer, a tiny transistor so fast and sensitive that it can count individual electrons as they pass through a circuit. The device could be useful in developing highly miniaturized computer circuits as well as improved light sensors for more powerful telescopes and microscopes. It also could help establish a standard of electrical current.

The single-electron transistor -- a device so small that it can be switched by only one electron -- is about 1,000 times faster than the previous record holder and 1 million times faster than a typical single-electron transistor, according to a report in the May 22 issue of the journal Science by Robert J. Schoelkopf, associate research scientist in applied physics . Other members of the research team were Daniel E. Prober, professor of applied physics and physics, and graduate student Alexay Kozhevnikov, both of Yale; and Professor Per Delsing and graduate student Peter Wahlgren of Chalmers Institute of Technology, Göteborg, Sweden.

Single-electron transistors have been around for about a decade, but were limited in their applications because of slow speeds and higher than expected noise levels. The Yale/Chalmers scientists developed a variant called the Radio Frequency Single-Electron Transistor, or RF-SET, which has greatly improved speed and the sensitivity to detect charges as small as 15-millionths of an electron. "We believe the performance of this device can approach the quantum limit for these kinds of electrical measurements," Schoelkopf says.

Researchers are working to make computer chips smaller and smaller, and they eventually will reach the level where quantum mechanical effects become important and the usual rules are no longer valid, contends Schoelkopf. For example, at quantum scales electrons behave more like waves than particles and can do unexpected things like tunnel through barriers, he explains.

By creating components that exploit these unusual quantum properties, scientists hope to vastly increase the power of computers. "With the ability to follow the individual electrons with the RF-SET device, we will be able to study such effects in ways we hadn't thought possible before," says Schoelkopf.

A limitation of the RF-SET and most other single-electron devices is that they presently work only at temperatures near absolute zero, or about -459 degrees Fahrenheit, thus requiring bulky refrigeration. Scientists at Yale and elsewhere are exploring ways to make them work more effectively at higher temperatures.

On the plus side, the new single-electron transistor could prove useful for improved sensors of photons, including electromagnetic emissions in the ultraviolet, visible or infrared ranges, say researchers. Many of the most sensitive of these detectors, which operate by converting light into an electrical signal, already require refrigeration. It is believed that using the new transistor to amplify the electrical signal produced by the light could improve their performance.

As an example, other research in Prober's group concentrates on devices for ultraviolet and visible imaging, which could compete with highly sensitive CCD (charge-coupled device) sensors. Prober's new low-temperature, superconducting devices would simultaneously provide images and give information about energy of the light received, which conventional devices cannot. "It could serve as an imaging detector and spectrometer combined into one, capable of determining chemical composition, density and temperature of a distant star," says Prober.

In addition to their use in astronomy, Prober's photodetectors could have major applications in other fields of science, including more powerful microscopes for biology and medicine.


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