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17 Jun 2002
Using an optical lattice of interfering laser beams, researchers make a type of matter never seen before.
Physicists in Germany have generated what they call a "special" state of matter, using a three-dimensional optical interference pattern. Turning up the intensity of this pattern created a gaseous "Mott insulator".
In the Mott state, repulsion between atoms restricts their motion in the lattice. This makes the material act like an insulator. This Mott state has only been previously seen in solids.
Immanuel Bloch and colleagues at the Max-Planck Institut für Quantenoptik in Garching, Ludwig-Maximilian-University in Munich, and ETH Zurich in Switzerland, first made a Bose-Einstein condensate (BEC) from ultracold atoms. They then took three laser-generated interference patterns and superimposed them orthogonally. This created a "light crystal" in which the intensity maxima trap atoms in the BEC - just like optical tweezers.
When the light field's strength was increased, the BEC state underwent a phase transition and turned into a Mott insulator. According to the team, the physical theories that describe interactions in the BEC no longer apply in the Mott state, and new theories to describe its atomic interactions are now needed.
By increasing or decreasing the light intensity from the lasers, the gas can be reversibly switched between a BEC "superfluid" and a Mott insulator. Bloch and colleagues say that this gives them full control over the optical lattice, and therefore the material's phase. Such control is not possible for a solid Mott insulator.
To detect these two states of matter, the researchers used another laser to illuminate the sample. In the BEC superfluid, this generates a matter-wave interference pattern, which is imaged onto a standard CCD camera. In the Mott insulator state, no such pattern is seen.
Now that physicists have the ability to switch between states and create a Mott insulator, the team believes that its work could lead to a better understanding of effects such as superconductivity, as well as providing a new tool for quantum computing and precision metrology.
Author
Michael Hatcher is technology editor of Opto & Laser Europe magazine.
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