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Martin Zwierlein answers a
few questions about this month's fast breaking paper in the field of
Physics.
From
•>>February 2005
Field:
Physics
Article Title: Condensation of pairs of fermionic atoms near a Feshbach resonance - art. no. 120403
Authors: Zwierlein,
MW;Stan, CA;Schunck, CH;Raupach, SMF;Kerman, AJ;Ketterle, W
Journal: PHYS REV LETT
Volume: 9212
Page: 403-403
Year: MAR 26 2004
* MIT, Dept Phys, MIT Harvard Ctr Ultracold Atoms, Cambridge, MA 02139 USA.
* MIT, Dept Phys, MIT Harvard Ctr Ultracold Atoms, Cambridge, MA 02139 USA.
* MIT, Elect Res Lab, Cambridge, MA 02139 USA.
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 Why
do you think your paper is highly cited?
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“Through the study of this novel system, physicists might be led to a better understanding of superfluidity and superconductivity in general, which could pave the way to the invention of new materials with "designed" properties, the ultimate dream being a room-temperature superconductor.”
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Superfluidity in strongly interacting atomic Fermi gases is
currently a rapidly advancing field of research in atomic physics,
with many theoretical and a growing number of experimental groups
joining in for the excitement. The breakthrough came with the
Bose-Einstein condensation of molecules, tightly bound pairs of
fermionic atoms, in November 2003 in Boulder, Innsbruck, and in
our group at MIT. Using these molecular condensates as the
starting point, we can now access a new regime in which the
molecules loosen up their bonds and become large, comparable to,
or even larger than the average distance between particles. This
strongly interacting "soup" of fermions finds its
analogies in such exotic systems as nuclear matter or neutron
stars.
Does
it describe a new discovery or a new methodology that's useful to
others?
Together with work from other groups, it does present a new
discovery. We observe fermion pair condensates in lithium-6 and
find them to be very pure, in contrast to the case of
potassium-40. It is foreseeable that ultracold atomic Fermi
gases will become an experimental test-bed for many-body
theories, just like bosonic atom gases represent the paradigm of
Bose-Einstein condensation. The future goal is to create an
artificial crystal of atoms trapped in interfering laser beams,
in which all parameters can be set by the experimenter, like the
lattice spacing and depth as well as the interaction strength
between particles. From these idealized systems people hope to
gain insight into the workings of strongly correlated systems,
most prominently superconductors with high critical temperature.
Could
you summarize the significance of your paper in layman's terms?
Bose-Einstein
Condensates
(BEC) is the mechanism
responsible for superfluidity in helium and superconductivity in
metals. It occurs at very low temperatures, when bosons,
particles with integer spin, tend to all gather in the state of
lowest energy and form a condensate. Fermions (particles with
half-integer spin), like electrons in a metal or the lithium-6
atoms we use in our experiment, cannot form such a condensate by
themselves. They have to first find a partner to form a bosonic
pair. These pairs of fermions can then condense just like
bosonic atoms. The nature of the pairs depends on how strong the
particles attract each other. They can be either tightly bound
into small molecules, which are stable even in free space, or
they can form very loose pairs, which can only exist because of
the stabilizing presence of all the other particles in the gas.
For very small attraction, this latter form of pairing is known
from electrons in superconducting metals. In our experiment, we
can smoothly tune the attraction between the fermions and
observe condensates of either tiny molecules or of large pairs
of fermions. It is the latter case which creates a lot of
excitement, since this finding provides strong evidence for
superfluidity in this interesting regime, where pairing would
not occur in free space but is induced by the presence of the
surrounding cloud of atoms.
Through the study of this novel system, physicists might be
led to a better understanding of superfluidity and
superconductivity in general, which could pave the way to the
invention of new materials with "designed" properties,
the ultimate dream being a room-temperature superconductor.
How
did you become involved in this research?
The machine on which the experiments have been conducted is
the same which produced the first Bose-Einstein
condensates
of sodium atoms in 1995. I joined Wolfgang Ketterle's group as
an intern from the Ecole Normale Superieure in Paris in 2001.
That year, the machine was upgraded to a double-species
experiment which could cool fermionic lithium-6 sympathetically
with sodium. After receiving a diploma in theoretical physics in
Paris, I started my Ph.D. studies in 2002 on the same
experiment.
Martin Zwierlein
Research Assistant
Research Laboratory for Electronics
MIT-Harvard Center for Ultracold Atoms
and Department of Physics
Massachusetts Institute of Technology
Cambridge, MA, USA
 
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ESI Special Topics,
February 2005
Citing URL - http://www.esi-topics.com/fbp/2005/february05-MartinZwierlein.html
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