First Observation of Trapped Matter Waves (or Lasers and Quantum Mechanics!)

An illustration of Anderson localization. The green balloons represent disordered barriers that localize the sound of the trumpet at its source. | Photo by L. Brian Stauffer

You know, sometimes I hate the University of Illinois. Them and Purdue. Just as I’m starting to make headway on my backlog of science papers to blog about by speeding through research on economics and American attitudes towards homosexuals, they go and put a paper about quantum mechanics in my way.

And damn, this shit is confusing.

But here we go anyways. Nearly five decades ago, a fellow by the name of P.W. Anderson came up with a theory called strong localization, or Anderson localization. Yup, when you’re that smart, you get to name theories and physical phenomena after yourself.

To get into Anderson localization, you first have to have at least a small grasp of the particle-wave duality of matter. Hopefully at some point in high school you were taught that light behaves as both a particle and a wave. It carries minute amounts of energy like a particle but shows diffraction patterns like a wave. It’s weird.

But even weirder yet is that all matter has been shown to have this property. Spit electrons – something we know to be particles and have mass – through a couple of slits and you get a diffraction pattern just like light or sound waves.

Speaking of diffraction patterns, another important element of waves is that they can cancel each other out. Get a trough hitting a crest and it results in a big bunch of nothing.

So Anderson postulated that if you have tiny bits of matter traveling through a medium, and if that medium has a bunch of big imperfections in it that reflect the wave nature of the matter, it can become trapped. Like if a trumpet player is playing on a stage and surrounded by a bunch of big sound reflectors. Get enough of them arranged in the right place, and none of the sound will be able to escape.

The problem with this prediction is that it is impossible to test. Real materials just have too many imperfections that are impossible to remove, or to readily control.

Yet, Brian DeMarco and a team of physicists at the University of Illinois have managed to produce Anderson localization and prove its existence. They did it with a laser beam of green light. Ultra cold atoms were trapped inside of a speckled beam of green laser light; the speckles acting as the imperfections. Just as predicted, the team showed that the laser light could completely localize the atoms – the firest direct observation of three-dimensional Anderson localization of matter.

So why is this important?

Understanding how this phenomenon works is extremely important to advancing several fields, including ultrasonic waves in medical imaging, lasers for imaging and sensing, and electron waves for electronics and superconductors. Specifically, getting a hold on this could mean large steps towards understanding high temperature superconductors, or creating new ones.

DeMarco hopes to use the quantum-matter analogues to better understand and manipulate materials.

Eventually, he plans to use his measurements of Anderson localization and the mobility edge along with future work exploring other parameters to engineer materials to better perform specific applications – in particular, high-temperature superconductors.

“Comparing measurements on a solid to theory are complicated by our lack of knowledge of the disorder in the solid and our inability to remove it,” DeMarco said. “But, that’s exactly what we can do with our experiment, and what makes it so powerful and exciting.”


About bigkingken

A science writer dedicated to proving that the Big Ten - or the Committee on Institutional Cooperation, if you will - is more than athletics.
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