QUANTA

Thursday, September 8, 2011

 Good vibrations for future quantum computers

École Polytechnique Fédérale de Lausanne (EPFL) physicists have developed a new theory that shows that dot symmetry in quantum dots (semiconductors that emit light) is enough to account for most of the intriguing optical properties of  the quantum dot, a building block for quantum computers.

Determining the optical properties of these quantum dots is a complicated and computationally intensive endeavor. So physicists at EPFL Laboratory of Physics of Nanostructures have proposed, and observationally verified, a new physical theory that reduces the time needed to perform these calculations and to better understand quantum dots.

When electrical charges are injected into quantum dots, they start to vibrate. This is what physicists call the wave function, which in this case vibrates a bit like the head of a drum. One would think that simulating these vibrations would be extremely complex, but the physicists realized that the wave behavior, and thus the light emitted by the quantum dot, could be determined sufficiently by symmetry. Because of this, the calculation could be simplified using a familiar mathematical tool known as group theory.

The strength of this approach is its relative simplicity. The physicists can deduce the optical properties of quantum dots based on symmetries that they suspect are there, and then verify the presence of the symmetries experimentally. “Calculations that up to now required supercomputers can now be replaced by other calculations that can be done on the back of a napkin,” physicist Marc-André Dupertuis says. “Using proven observational methods, we can precisely deduct the exact symmetry of the quantum dot, as well as the properties of the electrical charge it contains and even what kind of photons it will emit.”

This information will be useful in designing new devices that could be used in quantum computers.

Read more: http://goo.gl/XZt17

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