| 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.
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