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Researchers Glimpse Artificial Molecules in Action

Photonics Spectra
Nov 1998
Daniel C. McCarthy

Research efforts between the University of Munich and the University of Delaware have resulted in a technique that excites artificial molecules in a manner resembling the way light excites real molecules. This deceptively abstract technology may open new doors for creating computer systems based on molecular or even biological logic. The work was performed at the Max Planck Institute for Solid State Research.


At 20 nm, quantum dots, or artificial molecules (the boxlike structures), are much larger than molecules but smaller than current semiconductor architectures. They share qualities of behavior that are similar to molecules, and research continues into harnessing their molecular logic to drive tomorrow's computer chips. Courtesy of the University of Munich.

It may be hard to believe, but presumably the day will come when semiconductor-based computers have reached their limit in speed and size. Artificial molecules that could create integrated circuit systems have been the subject of research before. The new technology, however -- which is analogous to spectroscopy -- may help to overcome technological challenges presented by these molecules, which function only at near-absolute-zero temperatures and at slow speeds.

"Using artificial molecules as models for real molecular-based computers is not outlandish," said project co-leader Daniel van der Weide, an associate professor of electrical and computer engineering at the University of Delaware in Newark. He said it could result in cheaper, smaller machines that could identify hazardous materials or spending patterns on credit applications.

With the team of professor Rogert H. Blick at the University of Munich, van der Weide used a microwave interferometer to examine electron oscillations between two artificial molecules, or quantum dots. These oscillations behave similarly to Rabi oscillations, which are the characteristic movement of electrons between real molecules.

Blick and van der Weide's technique forced oscillating electrons to interact with two high-frequency pulses of electromagnetic radiation (2 to 400 GHz).

The pulses corresponded with the energy level of the artificial molecule and carried nearly identical frequencies. Thus, researchers could record electron responses to each pulse.

"We've basically been able to show that the coupled semiconductor quantum dots that we call artificial molecules behave more like real molecules than previously thought," van der Weide said.


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