Creating a quantum gas

Feb 01, 2010 By Miranda Marquit feature

(PhysOrg.com) -- "One of the many reasons people study ultracold gases is for their potential as model quantum systems," Deborah Jin tells PhysOrg.com. "There is a need to model quantum many-body systems because a lot of important physics - from condensed matter and material physics to nuclear and particle physics - increasingly require an understanding of complicated quantum behavior. Ultracold gases can possible provide that through models we can interact with, helping to close the gap between what we can describe theoretically and what actually happens."

Jin is a NIST physicist and a scientist at JILA, one of the leading science research institutes in the U.S., located at the University of Colorado campus in Boulder. Jin, along with fellow NIST scientist Jun Ye and their team of researchers have prepared a molecular quantum gas in a single hyperfine state, resulting in control over the final remaining degree of freedom needed to control all aspects of in an ultracold gas. The group’s work has been published in : “Controlling the Hyperfine State of Rovibronic Ground-State Polar Molecules.”

“To see , we want all the particles to be indistinguishable from each other,” Jin explains. “All of the atoms or molecules in the gas have to be in exactly the same internal state.” She says that some ultracold gases have approached this point, but the one thing lacking has been control over the hyperfine state, which accounts for nuclear spin inside the atoms that make up the molecules that form the gas.

“It seems that this degree of freedom is not worth worrying about, and in most and in chemistry, it really doesn’t matter, since the amount of energy is so small. But for quantum behavior, even that should be lined up. We describe how to identify and control what’s going on inside the nucleus,” Jin says.

In order to create a situation allowing control over the hyperfine state, the group at JILA first used improved spectroscopy techniques to identify the state of the molecules. The state of the molecules needed to be identified, and the molecules needed to be brought to their ground state. In order to do this, the group built on techniques used for hotter samples. “It’s hard to change nuclear spin, since it is weakly interacting,” Jin says. “But it is easy to drive from non-rotating to rotating, and there is a weak coupling. We use a microwave field to drive rotation, and then bring the molecule back to non-rotating, but with a different nuclear spin.”

“With control of this final degree of freedom, we can say that we truly do have a ,” Jin insists. “If we can get the gas a little colder, we should really be able to see the quantum mechanics involved.”
Before that point is reached, however, there are some steps that need to be taken. “We need a greater understanding of ultracold chemistry first, and we need to study how to ‘turn on’ the polar part of the molecules we use, figuring out what happen when we align them using the proper field,” Jin says.

“We are making rapid progress, though,” she continues. “We are quite close, closer than ever before, to being able to model interesting quantum behavior with ultracold polar molecules. And once we do that, there is a whole new world of science ahead.”

Explore further: Step lightly: All-optical transistor triggered by single photon promises advances in quantum applications

More information: Ospelkaus, et. al., “Controlling the Hyperfine State of Rovibronic Ground-State Polar Molecules,” Physical Review Letters (2010). Available online: link.aps.org/doi/10.1103/PhysRevLett.104.030402

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El_Nose
5 / 5 (1) Feb 01, 2010
I've never really understood that logic -- To understand the real world we need to create a model that in no way would ever exist in the real world. And it so rarely works in the real world the way the model works.

Now if we are creating this fictious model just to gain an understanding of a couple of concepts fine -- but don;t say its a model of the real world -- or a real system.. cause it isn't.

When simulating a star going nova physicists model a 2D plane or a thin slice of the star while this model seems reasonalbe and consistant for about 45% of observeable post nova stars it cannot explain most of the observable nova/supernova explosions results...
stuntmonkey
5 / 5 (2) Feb 02, 2010
I think I see your point. These authors appear to be using the word "model" in an unusual way, to mean an experimental system that connects (precisely or not) to some theoretical construct. Biologists use the term similarly, as in "mice are a model of human physiology". In physics it is more common to see "model" describing the theoretical construct itself, which may or may not have a close relationship with some real-world experiment.

Terminology aside, it's clear what they aim to do: Observe interesting quantum behavior in this molecular system, and use that behavior to test predictions from many-body quantum theory.