388 research outputs found
Optical detection of a BCS phase transition in a trapped gas of fermionic atoms
Light scattering from a spin-polarized degenerate Fermi gas of trapped
ultracold Li-6 atoms is studied. We find that the scattered light contains
information which directly reflects the quantum pair correlation due to the
formation of atomic Cooper pairs resulting from a BCS phase transition to a
superfluid state. Evidence for pairing can be observed in both the space and
time domains.Comment: 8 pages, 4 figures, revte
Finite range corrections near a Feshbach resonance and their role in the Efimov effect
We have measured the binding energy of Li Feshbach molecules deep into
the non-universal regime by associating free atoms in a Bose-Einstein
condensate by modulating the magnetic field. We extract the scattering length
from these measurements, correcting for non-universal short-range effects using
several different methods. We find that field-dependent effective range
corrections agree well with the data.
With this more precise determination of the scattering length vs. field we
reanalyze our previous data on the location of atom loss features produced by
the Efimov effect \cite{PollackSci09} and investigate effective range
corrections to universal theory.Comment: Accepted for publication in Phys. Rev.
Peace in Persecution: A Series of Sermons on the First Epistle of Peter
The First Epistle of Peter is a letter of encouragement and exhortation to a suffering people. The purpose of this study is to examine the Apostle\u27s letter and other pertinent materials to discover what it meant in the life situation of those to whom it was sent. Then as a final product of that examination, the eternal truths that transcend all time have been presented in this series of sermons in a style that communicates to the modern Christian.
The Apostle tells us that we can have Peace in Persecution
Growth and Collapse of a Bose Condensate with Attractive Interactions
We consider the dynamics of a quantum degenerate trapped gas of Li-7 atoms.
Because the atoms have a negative s-wave scattering length, a Bose condensate
of Li-7 becomes mechanically unstable when the number of condensate atoms
approaches a maximum value. We calculate the dynamics of the collapse that
occurs when the unstable point is reached. In addition, we use the quantum
Boltzmann equation to investigate the nonequilibrium kinetics of the atomic
distribution during and after evaporative cooling. The condensate is found to
undergo many cycles of growth and collapse before a stationary state is
reached.Comment: Four pages of ReVTeX with four postscript figure
The Superfluid State of Atomic Li6 in a Magnetic Trap
We report on a study of the superfluid state of spin-polarized atomic Li6
confined in a magnetic trap. Density profiles of this degenerate Fermi gas, and
the spatial distribution of the BCS order parameter are calculated in the local
density approximation. The critical temperature is determined as a function of
the number of particles in the trap. Furthermore we consider the mechanical
stability of an interacting two-component Fermi gas, both in the case of
attractive and repulsive interatomic interactions. For spin-polarized Li6 we
also calculate the decay rate of the gas, and show that within the mechanically
stable regime of phase space, the lifetime is long enough to perform
experiments on the gas below and above the critical temperature if a bias
magnetic field of about 5 T is applied. Moreover, we propose that a measurement
of the decay rate of the system might signal the presence of the superfluid
state.Comment: 16 pages Revtex including 10 figures, submitted to Phys. Rev.
Deformation of a Trapped Fermi Gas with Unequal Spin Populations
The real-space densities of a polarized strongly-interacting two-component
Fermi gas of Li atoms reveal two low temperature regimes, both with a
fully-paired core. At the lowest temperatures, the unpolarized core deforms
with increasing polarization. Sharp boundaries between the core and the excess
unpaired atoms are consistent with a phase separation driven by a first-order
phase transition. In contrast, at higher temperatures the core does not deform
but remains unpolarized up to a critical polarization. The boundaries are not
sharp in this case, indicating a partially-polarized shell between the core and
the unpaired atoms. The temperature dependence is consistent with a tricritical
point in the phase diagram.Comment: Accepted for publication in Physical Review Letter
Bright soliton trains of trapped Bose-Einstein condensates
We variationally determine the dynamics of bright soliton trains composed of
harmonically trapped Bose-Einstein condensates with attractive interatomic
interactions. In particular, we obtain the interaction potential between two
solitons. We also discuss the formation of soliton trains due to the quantum
mechanical phase fluctuations of a one-dimensional condensate.Comment: 4 pages, 2 figures, submitted to PR
Extreme tunability of interactions in a Li Bose-Einstein condensate
We use a Feshbach resonance to tune the scattering length a of a
Bose-Einstein condensate of 7Li in the |F = 1, m_F = 1> state. Using the
spatial extent of the trapped condensate we extract a over a range spanning 7
decades from small attractive interactions to extremely strong repulsive
interactions. The shallow zero-crossing in the wing of the Feshbach resonance
enables the determination of a as small as 0.01 Bohr radii. In this regime,
evidence of the weak anisotropic magnetic dipole interaction is obtained by
comparison with different trap geometries
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