The Grainger College of Engineering

UI group creates a disordered insulator in an optical lattice

7/28/2010

Researchers in Brian DeMarco's physics research group at Illinois have discovered a disorder-induced superfluid-to-insulator phase transition in a rubidium Bose–Einstein condensate trapped in an optical lattice. Their results, which are the first experimental confirmation of recent numerical simulations that predicted a superfluid–Bose glass transition, were reported this week in Nature Physics.

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Researchers in Brian DeMarco's physics research group at Illinois have discovered a disorder-induced superfluid-to-insulator phase transition in a rubidium Bose–Einstein condensate trapped in an optical lattice. Their results, which are the first experimental confirmation of recent numerical simulations that predicted a superfluid–Bose glass transition, were reported this week in Nature Physics.

 

Brian DeMarco in his lab
Brian DeMarco in his lab

“We use techniques from atomic physics and apply them to long-standing questions in condensed matter physics,” said DeMarco.

 

This approach—using one quantum system that we can control to elucidate another system that is beyond microscopic control—is called ‘quantum simulation’ and goes back to an idea first proposed by Richard Feynman in 1962.

“The microscopic effects of lattice defects and long-range electronic interactions, for example, are not well controlled in strongly correlated materials, and sophisticated theoretical approaches have reached inconsistent conclusions,” said DeMarco. “Simulating the impact of these effects on strongly correlated materials above absolute zero temperature is beyond the capabilities of even today’s supercomputers.”

 

Rubidium atoms isolated in an optical lattice.
Rubidium atoms isolated in an optical lattice.

The DeMarco group’s quantum simulator is a gas of ultracold 87Rb atoms, crystallized into an artificial solid using three pairs of 812-nm laser beams. In their experiment, the atoms play the role of the superconducting electron pairs in a solid, and the light, that of the underlying ionic crystal. The researchers apply an optical speckle field using a 532-nm laser to simulate the effects of disorder on the lattice.

 

According to DeMarco, “This system lets us to manipulate the atoms and introduce disorder controllably, so we can explore the effects of disorder in the weakly interacting and strongly correlated limit.”

Besides DeMarco, graduate students Matthew Pasienski, David McKay, and Matthew White carried out the research.

The work was supported by DARPA, the Sloan Foundation, NSERC, and the National Science Foundation. The conclusions are those of the authors and not necessarily of the funding agencies.
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Contact: Brian DeMarco, Department of Physics, 217/244-9848.

Writer: Celia M. Elliott, Department of Physics, 217/244-7725.

Image: Brian DeMarco

If you have any questions about the College of Engineering, or other story ideas, contact Rick Kubetz, Engineering Communications Office, 217/244-7716, editor.

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This story was published July 28, 2010.