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Classical Physics falls short
January 20, 2002With the aid of so-called quantum dots, PhD student Wilfred van der Wiel has gained new insight into quantum-mechanical processes. "This is one of the paths that could lead to smaller, but also fundamentally different electronics, " says Van der Wiel. He will receive his degree on 28 January for his fundamental research. Parts of his work, in which he goes beyond classical physics, are being published in Science and Nature magazines.
"Although 'nano' is no longer a scientific buzzword, there are still many fundamental questions to be answered," says Van der Wiel. His research, largely funded by FOM, is mainly aimed at two fundamental points: the making of artificial molecules using quantum dots, in other words, with artificial atoms, and the study of the interaction between the electron-spins in such an atom with its environment.
A quantum dot can be seen as a single electron transistor. Whereas, in a normal transistor, many electrons are allowed to pass simultaneously, a quantum dot will allow only one electron to pass at a time. Researchers in Delft have previously shown that quantum dots can be used to build artificial atoms. By entrapping a small number of electrons in quantum dot, one simulates a real atom. Just like in real atoms there is a periodic system for the different `elements.` Kouwenhovium is an example of such an artificial element. The atom was named after one of Van der Wiel`s supervising professors, Prof.Dr.Ir. Leo Kouwenhoven.
Van der Wiel: "The next logical step after the study of single quantum dots, is to research two joined dots - a two-atom artificial molecule." These structures offer a number of extra possibilities. One of the interesting possibilities is the use of the dots in quantum computing. There are ideas on using these double quantum dots as coupled quantum bits, or qubits: the building-blocks for quantum computing.
Another typical quantum-mechanical phenomenon is one that is very important in Van der Wiels work: the Kondo-effect. In contrast to what classical models predict, the electrical conductivity of metals with a small concentration of magnetic impurities decreases as the temperature gets closer to absolute zero (-273 degrees Celsius). The same laws that govern this effect, play an important part in artificial atoms. Van der Wiel: "We can not only accurately simulate natural systems in our dots, but we can also create systems that do not occur naturally. What makes this exciting is that we not only step away from classical physics, but we also need to create completely new quantum-mechanical descriptions to clarify our work."
Delft University of Technology
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