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Deborah S. Jin NIST physicist, JILA Fellow, and CU adjoint associate professor Opening Statement Press conference on Fermionic Condensates, Jan. 28, 2004

For Immediate Release: January 28, 2004

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Good morning. I am delighted to be here today to tell you about some exciting new results from our lab. I will start with a brief description of what we see in these experiments after which I will be happy to answer questions. Also, before we get started, I'd like to introduce my co-authors on this paper published today. This is Cindy Regal, a CU graduate student in physics, and Markus Greiner, a CU postdoctoral researcher.

What we report in this paper is the first observation of a fermionic condensate in an ultracold gas of atoms. This is a new form of matter that is related to a Bose-Einstein condensate and related to superconductivity. But our fermionic condensate is not a Bose-Einstein condensate and not a superconductor but really something new that may link these two behaviors. Let me try to explain further.

First of all, what we actually do in the lab is to cool a small amount of gas down to temperatures very near absolute zero. This gas is confined inside an ultrahigh vacuum chamber and we manipulate and study it using magnetic fields and laser light. Now this gas happens to be made up of potassium atoms that are fermions.

Let me remind you that all particles, including atoms, can be classified as fermions or bosons. (This is basic quantum mechanics). Bosons by their nature are copy cats; this can lead to Bose-Einstein condensation where all the bosons do exactly the same thing. Fermions, which by the way are the building blocks of all visible matter, are instead by their nature independent thinkers. They never do the same thing.

Yet we report today a condensate in a gas of fermionic atoms. How is this possible? It is possible through pairing of fermions to make bosons. This is similar to what happens to electrons in superconductivity. To explain this I will use an analogy illustrated in this poster. The dancers in the top picture are our individualistic fermionic atoms. They look like they are moving quite independent of one another, and yet if we look more closely there are pairs in this gas. It is subtle but you can identify the pairs by the dancers' eye contact and body language. These pairs are bosons and can undergo condensation.

But how can we see this condensation of pairs of fermions? We suddenly bring together the two atoms (or dancers here) in each of these subtle pairs, as in the bottom picture. When we look at the motion of these bound pairs, the condensation becomes apparent.

It is this condensation of pairs of fermions that we created and observed in our very cold potassium gas. In this poster are three images of the fermionic condensate, taken for different strengths of the attraction that causes the pairing. The fermionic condensate appears in these images as the large central spike, which corresponds to pairs of atoms that have near zero velocity.

This fermionic condensate is closely related to what happens in a superconductor. However, in order to compare to a superconductor, you have to realize that our atoms are much heavier than electrons and our gas is much less dense than a solid. When you account for these differences, our atoms are more strongly attracted to each other. And if you could make electrons in a superconductor do this, you would get a room temperature superconductor.

To sum it up, our work, creating this exotic form of matter—a Fermi condensate in an ultracold gas—provides a new example of a dramatic quantum behavior. This work gives the scientific community a new tool for understanding the basic physics behind superconductivity.

At this point, I will be happy to answer your questions.