Good vibrations for future quantum computers

Sep 07, 2011
Top of a quantum dot © Alexander Kleinsorge

( -- The enigmatic quantum dot is the basic building block for quantum computers. EPFL physicists have developed a new theory which shows that dot symmetry is enough to account for most of their intriguing optical properties.

Physicists have created a pyramidal dot that’s just shy of 100 nanometers high, about 200 atoms on a side. By applying voltage to this miniature structure, the scientists have created a device that can emit light, which could then be used in future components of quantum computers. But the road to this new kind of computing is still long, particularly because determining the of these is a complicated and computationally intensive endeavor. Marc-André Dupertuis and his team from EPFL’s Laboratory of Physics of Nanostructures have proposed, and observationally verified, a new physical theory that not only reduces the time needed to perform these calculations, but also, and above all, allows us simply to better understand the nature of these strange objects.

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 Dupertuis realized that the wave behavior, and thus the light emitted by the quantum dot, could be determined sufficiently by . Because of this, the calculation could be simplified using a familiar mathematical tool known as group theory.

Better understanding on the back of a napkin

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,” Dupertuis says.

Dupertuis had to overcome a serious difficulty in order to come up with the theory – he had to be able to simplify it sufficiently, while still taking into account the strange properties that govern the quantum world. Imagine a cake cut into symmetric slices, but whose edges don’t all look the same; you’d have to arrange the slices in a specific order to put the cake back together again. This is the kind of mathematical and quantum challenge that the physicist is tackling.

A promising advance

This obstacle aside, the method is very promising. “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.

Explore further: New nanogenerator harvests power from rolling tires

More information: Symmetries and the polarized optical spectra from exciton complexes in quantum dots, M. A. Dupertuis, K. F. Karlsson, D. Y. Oberli, et al., Physical Review Letters, 06.09.2011

Related Stories

Single quantum dot nanowire photodetectors

Dec 14, 2010

Moving a step closer toward quantum computing, a research team in the Netherlands recently fabricated a photodetector based on a single nanowire, in which the active element is a single quantum dot with a ...

Quantum dots are not dots: physicists

Dec 21, 2010

Researchers from the Quantum Photonics Group at DTU Fotonik in collaboration with the Niels Bohr Institute, University of Copenhagen surprise the scientific world with the discovery that light emission from ...

In Brief: Quantum dot-Induced transparency

Dec 01, 2010

Using rigorous and realistic numerical simulations, staff in the Nanophotonics and Theory and Modeling groups at the Argonne National Laboratory have recently demonstrated that a single semiconductor nanocrystal, ...

Recommended for you

Nanowires could be the LEDs of the future

Jun 24, 2015

The latest research from the Niels Bohr Institute shows that LEDs made from nanowires will use less energy and provide better light. The researchers studied nanowires using X-ray microscopy and with this ...

Researchers detect spin precession in silicon nanowires

Jun 24, 2015

Scientists at the U.S. Naval Research Laboratory (NRL) have reported the first observation of spin precession of spin currents flowing in a silicon nanowire (NW) transport channel, and determined spin lifetimes ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Sep 08, 2011
I love these sorts of stories. I've always leaned a bit closer to the engineering side of the engineer/scientist bridge, and the above strikes me as more of an engineering type of issue. I.e, it may not be as accurate and take into account as many variables, but it provides an answer that is more than good enough to continue on with whatever is being made.

Nothing against scientists of course, but I'm sure there are many engineers on here who have worked with scientists who know what I'm talking about...

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.