to exploit Bose-Einstein condensation, quantum
degenerate Fermi gases,
and cold molecules for
metrology and ultralow-temperature
physics.
INTENDED OUTCOME AND BACKGROUND
The Quantum Physics Division and
JILA are world renown for studies of
Bose-Einstein condensates and quantum
degenerate Fermi gases. The exemplary
JILA collaboration between NIST and
the University of Colorado (CU) led to
the achievement of the first Bose-Einstein condensate by Eric Cornell
(NIST) and Carl Wieman (CU), who
together received the 2001 Nobel Prize
in Physics. This achievement, coupled
with the creation of the first quantum
degenerate Fermi gas and the first Fermi
condensate by MacArthur Prize-winner
Deborah Jin (NIST), places the
Quantum Physics Division and JILA at
the forefront of studies of macroscopic
quantum mechanical systems.
A better understanding of these systems
is critical as the miniaturization of electronic
components pushes into the size
region where quantum mechanical
effects play a significant role in their
operation. Additionally, these systems
provide unique opportunities for
metrology and for gaining insights into
analogous transitions in technologically
important solid-state systems. We plan
to continue to explore the new quantum
mechanical systems that these discoveries
have made accessible and to maintain
our leadership position. The development
of techniques to produce ultracold
molecules also promises important
advances in chemical physics.
Accomplishments
BEC on a Chip
We have succeeded in creating an atom
interferometer on a lithographically patterned
microstructure, an "atom chip."
The long-term technical goal of this
work is to develop supersensitive and
compact inertial sensors, e.g., gyroscopes
and gravity gradiometers.
A condensate of ultracold atoms is guided
along an invisible magnetic track
generated by currents carried in tiny
wires. The condensate is split coherently
into two parts that travel a short distance
in opposite directions along the
track. Then the directions are reversed,
the two parts of the condensate recombine,
and we observe patterns of high
and low density--atom-wave interference
fringes. The patterns of these
fringes are sensitive to any acceleration
felt by the chip during the period when
the two parts of the condensate were
separated.
In this first realization, the sensitivity
is limited by the relatively short time
the condensate parts remain separated.
Future work will concentrate on
improving performance.
Destroying BEC
Ironically, one of the more important
scientific advances in our recent ultracold
research is progress towards
destroying a Bose-Einstein condensate.
As a ball of Bose-condensed gas starts to
rotate, it becomes pierced by progressively
more tiny tornadoes known as
quantized vortices. When the rotation
rate is very high, these vortices organize
themselves into a tightly packed triangular
array. At the highest level of rotation,
the size of each vortex becomes large
compared to the spacing between them.
Theory predicts a reordering transition
in which the condensate is destroyed
and replaced by a highly correlated gas,
reminiscent of the quantum Hall state
in solids. Achieving and characterizing
this transition is a prime scientific goal
because we believe it will generate
important insights into analogous transitions
in technologically important,
condensed-matter systems, such as the
giant-magnetoresistance phenomenon
that is used in disk-drive read-sensor technology.
In the last two years we have come
much closer to achieving our goal. We
have installed high-intensity lasers that
we hope will soon bring us even closer.
Cold Fermions and
Resonance Superfluidity
Figure 3. MacArthur Prize-winner Deborah Jin,
with her CU graduate student Cindy Regal and
CU postdoctoral research associate Marcus
Greiner.
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Our work on cold Fermi gases has progressed
at a rapid pace. In January 2004,
we reported the first observation of a
"Fermi condensate." This novel phase of
matter was predicted in 2001 by JILA's
Murray Holland (CU), who coined the
term "resonance superfluidity" because
of the key role of a magnetic-field
Feshbach resonance in creating these
condensates of fermionic-atom pairs.
Our experimental observation, which
included a measurement of the temperature
and magnetic-field phase diagram,
revealed a surprisingly high transition
temperature (relative to the Fermi temperature).
It triggered a great deal of
experimental and theoretical work
exploring this new Fermi superfluid
phase. Because of the unique control
we have in ultracold gas systems, future
studies of the Fermi condensate have
the potential for dramatically enhancing
our understanding of the connection
between superconductivity and
Bose-Einstein condensation.
Progress leading up to the Fermi-condensate
observation yielded a number of
important advances, including the first
spectroscopic measurements of the interaction
energy in a Fermi gas near a
Feshbach resonance, the first reversible
conversion (pairwise) of the majority of
trapped ultracold atoms into ultracold
molecules, and a direct measurement of
the binding energy of these molecules
with the introduction of RF photodissociation.
Bose-Fermi Mixtures
We are now exploring Bose-Fermi mixtures.
We employ sympathetic cooling
to produce Bose-Einstein condensates of
87Rb atoms simultaneously trapped with
a Fermi gas of 40K atoms.
Focusing on interactions in the gas mixture,
we perform collision studies to
measure the magnitude of the interspecies
scattering length between the
87Rb and 40K atoms. This single parameter
characterizes the interactions
between the boson and fermion atoms
and thus controls many of the equilibrium
and dynamic properties of the ultracold
gas mixture. By using an optical
dipole trap and manipulating the atoms'
spin states, we recently observed four
heteronuclear Feshbach resonances.
These resonances open up the possibility
for controlling the interactions in the
gas. They also provide a means for creating
ultracold, weakly bound heteronuclear
molecules.
First strategic focus |
Second strategic focus |
Third strategic focus |
Fourth strategic focus
"Technical Activities 2004" - Table of Contents |
