24 December 2011

New Technique For Cooling Quantum Gases

Physicists find a new way to cool quantum gases.

By using a quantum algorithm to remove excess energy, physicists at Harvard University have found a new way to cool synthetic materials. It is the first application of the technique to ulta-cold atomic gasses; "algorithmic cooling". This research may pave the way to new discoveries from materials science to quantum computation.

The research is published in the journal Nature.

"Ultracold atoms are the coldest objects in the known universe," explains senior author Markus Greiner, associate professor of Physics at Harvard. "Their temperature is only a billionth of a degree above absolute zero temperature, but we will need to make them even colder if we are to harness their unique properties to learn about quantum mechanics.

Greiner and his colleagues study quantum many-body physics, the exotic and complex behaviors that result when simple quantum particles interact. It is these behaviors which give rise to high-temperature superconductivity and quantum magnetism, and that many physicists hope to employ in quantum computers.

"We simulate real-world materials by building synthetic counterparts composed of ultra-cold atoms trapped in laser lattices," says co-author Waseem Bakr, a graduate student in physics at Harvard. "This approach enables us to image and manipulate the individual particles in a way that has not been possible in real materials."

Video: A Guide to Quantum Mechanics

Observing the quantum mechanical effects that Greiner, Bakr and colleagues seek requires extreme temperatures.

"One typically thinks of the quantum world as being small," says Bakr, " but the truth is that many bizarre features of quantum mechanics, like entanglement, are equally dependent upon extreme cold."

When an object gets hotter, more of its constituent particles are being moved around. This obscures the quantum world just like when shaken camera blurs a photograph.

The push to ever-lower temperatures is driven by techniques like "laser cooling" and "evaporative cooling," which are approaching their limits at nanoKelvin temperatures. In a proof-of-principle experiment, the Harvard team has demonstrated that they can actively remove the fluctuations which constitute temperature, rather than merely waiting for hot particles to leave as in evaporative cooling.

Almost like placing or fitting one egg per slot in an egg carton, the process of orbital excitation blockade removes the excess atoms from a crystal until there is precisely one atom for each site.

"The collective behaviors of atoms at these temperatures remain an important open question, and the breathtaking control we now exert over individual atoms will be a powerful tool for answering it," said Greiner. "We are glimpsing a mysterious and wonderful world that has never been seen in this way before."
Greiner and Bakr's co-authors in Harvard's Department of Physics are Philipp Preiss, Eric Tai, Ruichao Ma and Jonathan Simon.

Their work was supported by the Army Research Office through the DARPA OLE program, the AFOSR MURI program, and by grants from the NSF.

Harvard University
Harvard's Department of Physics
Air Force Office of Scientific Research (AFOSR)
National Science Foundation
Army Research Office
Defense Advanced Research Projects Agency (DARPA)
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