Bose-Einstein and Fermi-Dirac Gases:
to exploit Bose-Einstein condensation and
quantum-degenerate Fermi gases for metrology and ultralow-temperature
physics.
INTENDED OUTCOME AND
BACKGROUND
The Quantum Physics Division and JILA are today a world focal point
for studies of Bose-Einstein condensates and quantum-degenerate Fermi gases.
The mutual advantage to NIST and the University of Colorado in collaborating at
JILA was best exemplified when Eric Cornell (NIST) and Carl Wieman (CU)
together achieved for the first time a Bose-Einstein condensate, and for that
accomplishment were awarded the 2001 Nobel Prize in Physics. Coupled with
the creation of the first quantum-degenerate Fermi gas by Deborah Jin (NIST)
and one of her CU graduate students, Brian DeMarco, this places the Quantum
Physics Division and JILA at the forefront of studies of macroscopic - and
therefore easily studied - quantum-mechanical systems.
A better understanding of these systems is critical today because the
miniaturization of electronic components is pushing into the size region where
quantum-mechanical effects play a significant role in their operation. We plan
to continue to explore and exploit the new quantum-mechanical systems that
these discoveries have made accessible, and maintain our leadership position.
Additionally, a program to use current-carrying wires as "pipes" to
both guide and "split" cold atoms for atom interferometry is being
aggressively pursued.
Accomplishments
Frequency Shift Metrology
We are in the midst of a series of studies to understand the microwave
transition in ultracold rubidium. Ultracold temperatures and magnetic-trapping
technology make possible interrogation times extending to 2 s, which leads
to very narrow line widths and correspondingly higher precision.
Residual interactions between the atoms cause shifts in the transition
frequency that must be accounted for. We can track these small shifts with
great accuracy since the extended interrogation time makes it possible to
follow the frequency shifts as the cloud heats, cools, decoheres, and even
undergoes a phase transition into or out of a Bose-condensed state.
Many of the observed effects are quite counterintuitive, and therefore help us
reshape our understanding of what it means for a sample of gas to lose its
internal coherence.
BEC on a Chip
In other cold-boson work, we have
succeeded in injecting a condensate into a
lithographically patterned microstructure,
an "atom chip." The long-term technological
goal of this work is to develop
super-precise inertial sensors, i.e., gyroscopes
and gravity gradiometers. The
condensate will travel through the chip and
be coherently split and recombined. The
resulting interference signal will be exquisitely
sensitive to minute inertial effects.
For now, our very preliminary condensate-in-chip studies have demonstrated that
minute imperfections in the wire can have deleterious effects on the
condensate's coherence. Our new generation chips will be constructed with
considerably more attention to this issue.
"Destroying" BEC
Figure 1. Eric Cornell, co-discoverer (together with Carl Wieman) of
Bose-Einstein condensation in dilute atomic vapors. |
Ironically, one of the more important scientific advances in our ultracold
research this year is progress not towards creating a Bose-Einstein condensate
but towards destroying it. As a ball of Bose-condensed gas starts to rotate, it
becomes pierced by progressively more, tiny tornados 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
the vortices.
Theory predicts there will be a reordering transition in which the condensate
is destroyed, to be replaced by a highly correlated gas reminiscent of the
quantum Hall state in solids. Achieving and characterizing this transition in
the lab is a prime scientific goal, because we anticipate it will generate
important insights into analogous transitions in technologically important,
condensed-matter systems, including the giant-magneto-resistance phenomenon
that is so vital to progress in disk-drive read-sensor technology. During the
year we advanced the figure-of-merit for producing the transition a factor of
20 closer to the goal.
Cold Fermions
© Geoffrey
Wheeler
|
We successfully implemented a number of new experimental capabilities that
enhance our research opportunities in exploring Fermi gases of cold atoms. We
developed a far-off-resonance, optical-dipole trap for confining fermionic atoms
in any combination of hyperfine spin-states. This trap will be used to search
for a new superfluid phase driven by resonant interactions in the gas.
To this end, we made the first measurement of a magnetic-field-tunable,
Feshbach scattering resonance for fermionic atoms. This resonance allows us to
control interaction strengths and is a key ingredient for realizing resonance
superfluidity as predicted by Holland and co-workers. We have also measured the
first p-wave Feshbach resonance for fermionic atoms. This resonance
occurs in the scattering of atoms in the same spin-state and could provide a
mechanism for realizing superfluidity with p-wave Cooper pairs.
In another experiment, we demonstrated simultaneous cooling and trapping of
Bose and Fermi gases in the quantum regime. Bose-Einstein condensates are
produced using 87Rb atoms. Simultaneously trapped, fermionic
40K atoms are cooled sympathetically and reach roughly a quarter of
the Fermi temperature. Work is proceeding in characterizing this new system.
Figure 2. Deborah Jin aligns an infrared laser for a magneto-optical
trap. The trap is used to collect 1 billion rubidium atoms under
ultra-high vacuum. The atoms are then sent to a second trap under even higher
vacuum and cooled to 100 nanokelvin. The result is a so-called
"Bose-Einstein condensate" in which a large number of atoms behave
coherently.
First strategic focus |
Second strategic focus |
Third strategic focus
"Technical Activities 2002" - Table of Contents |
