Laser-cooled molecules could pave way for quantum computing
By Ben Coxworth
September 27, 2010
In order for quantum computers to become a reality, it would be hugely helpful if scientists were able to supercool molecules. If a temperature of near absolute zero (-273C/-460F) could be achieved, then the oscillations associated with the molecules’ low energies could be used in the creation of quantum bits for use in quantum processors. Recently, researchers at Yale University got a step closer to that goal, by using laser light to cool molecules.
Scientists have so far been taking two approaches in their efforts to create quantum bits, or qubits. One involves using individual atoms, although these reportedly don’t communicate with one another well enough. The other is to create so-called artificial atoms, made by combining billions of atoms within a circuit-like device that behaves like a single atom. These communicate much better, but are so large that they are subject to interference from the outside world.
"It's a kind of Goldilocks problem," said Yale physicist David DeMille, who led the project. "Artificial atoms may prove too big and individual atoms may prove too small, but molecules made up of a few different atoms could be just right."
The problem in working with molecules is that generally-speaking, they cannot be manipulated without disturbing their quantum properties. Other groups have tried cooling individual atoms, then stitching them together to form a molecule. DeMille, however, wanted to avoid that step. He was able to do so by hitting strontium monofluoride (SrF) molecules from opposite directions with steady laser-delivered streams of photons.
SrF molecules were chosen because they are less likely than others to start vibrating, and these particular SrF molecules came from a new source that allowed them to be pre-cooled better than was previously possible. The color of laser light chosen was also a factor, as it ensured that the energy absorbed by the molecules would not set them spinning – instead, it was re-emitted, which caused the molecules to lose some of their own kinetic energy in the process.
The group was ultimately able to get the SrF molecules’ temperature down to about 300 microkelvin, which is significant, but still not far enough... absolute zero is 0 kelvin. DeMille thinks that they can come closer to that temperature and that the process should work with other types of molecules. Additionally, he believes that the process will have applications beyond quantum computing.
"Laser cooling of atoms has created a true scientific revolution. It is now used in areas ranging from basic science such as Bose-Einstein condensation, all the way to devices with real-world impacts such as atomic clocks and navigation instruments," he stated. "The extension of this technique to molecules promises to open an exciting new range of scientific and technological applications."
The research is published in the journal Nature.
Via Nature News.