29. July 2010 10:06
Quantum phenomenon: Pinning atoms into order
Physicists can observe quantum mechanical phase transitions using ultracold atoms (yellow) in optical lattices (white surface). Image: Uni Innsbruck, Austria
A fundamental physical phenomenon that causes atoms to build an organized structure from an initially unorganized one has been observed for the first time by physicists at the University of Innsbruck in Austria. The research team headed by Hanns-Christoph Nägerl have published their research today in the scientific journal Nature.
The observations rely on studying a peculiar quantum state of matter known as a Bose-Einstein condensate. In this state a group of atoms shares the same quantum wave function, just like the photons in a laser beam, and quantum phenomena become measurable.
Using a Bose-Einstein condensate of cesium atoms scientists created one dimensional structures in an optical lattice created with laser beams. In these quantum lattices, or wires, the single atoms are aligned next to each other with laser light stopping them from breaking rank.
"Interaction effects are much more dramatic in low-dimensional systems than in three dimensional space," said Hanns-Christoph Nägerl, explaining why such material structures, whose dimensions do not extend to 3D, are highly interesting for physicists.
The Innsbruck team have observed a transition from a superfluid (Luttinger liquid) to an insulated phase (Mott-insulator). In their experiment they showed that for strongly interacting atoms an additional weak lattice potential was enough to pin the atoms to fixed positions along the wire. The atoms were cooled down to near absolute zero.
"It is not thermal fluctuations that induce the phase transition," stresses PhD student Elmar Haller, who is first author of the study. "In fact, the atoms are already correlated due to strong repulsive interaction and only need a small push to align regularly along the optical lattice," explains Haller. When the lattice is removed, the atoms return to a superfluid state.
The research has been co-funded through the European Science Foundation EUROCORES scheme under the EuroQUASAR (European Quantum Standards and Metrology) programme. Further funding came from the Austrian Science Fund (FWF) and by European Union research programmes.
Notes to editors
Pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons. Elmar Haller, Russell Hart, Manfred J. Mark, Johann G. Danzl, Lukas Reichsöllner, Mattias Gustavsson, Marcello Dalmonte, Guido Pupillo, Hanns-Christoph Nägerl. Nature 29 July 2010.
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Elmar Haller, University of Innsbruck
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