490 research outputs found
Radio-Frequency Spectroscopy of Ultracold Fermions
Radio-frequency techniques were used to study ultracold fermions. We observed
the absence of mean-field "clock" shifts, the dominant source of systematic
error in current atomic clocks based on bosonic atoms. This is a direct
consequence of fermionic antisymmetry. Resonance shifts proportional to
interaction strengths were observed in a three-level system. However, in the
strongly interacting regime, these shifts became very small, reflecting the
quantum unitarity limit and many-body effects. This insight into an interacting
Fermi gas is relevant for the quest to observe superfluidity in this system.Comment: 6 pages, 6 figure
Metastable neon collisions: anisotropy and scattering length
In this paper we investigate the effective scattering length of
spin-polarized Ne*. Due to its anisotropic electrostatic interaction, its
scattering length is determined by five interaction potentials instead of one,
even in the spin-polarized case, a unique property among the Bose condensed
species and candidates. Because the interaction potentials of Ne* are not known
accurately enough to predict the value of the scattering length, we investigate
the behavior of as a function of the five phase integrals corresponding to
the five interaction potentials. We find that the scattering length has five
resonances instead of only one and cannot be described by a simple gas-kinetic
approach or the DIS approximation. However, the probability for finding a
positive or large value of the scattering length is not enhanced compared to
the single potential case. The complex behavior of is studied by comparing
a quantum mechanical five-channel numerical calculation to simpler two-channel
models. We find that the induced dipole-dipole interaction is responsible for
coupling between the different |\Omega> states, resulting in an inhomogeneous
shift of the resonance positions and widths in the quantum mechanical
calculation as compared to the DIS approach. The dependence of the resonance
positions and widths on the input potentials turns out to be rather
straightforward. The existence of two bosonic isotopes of Ne* enables us to
choose the isotope with the most favorable scattering length for efficient
evaporative cooling towards the Bose-Einstein Condensation transition, greatly
enhancing the feasibility to reach this transition.Comment: 13pages, 8 eps figures, analytical model in section V has been
remove
Optical excitations in a non-ideal Bose gas
Optical excitations in a Bose gas are demonstrated to be very sensitive to
many-body effects. At low temperature the momentum relaxation is provided by
momentum exchange collisions, rather than by elastic collisions. A collective
excitation mode forms, which in a Boltzmann gas is manifest in a collision
shift and dramatic narrowing of spectral lines.
In the BEC state, each spectral line splits into two components. The doubling
of the optical excitations results from the physics analogous to that of the
second sound. We present a theory of the line doubling, and calculate the
oscillator strengths and linewidth.Comment: 5 pages, 3 eps figure
Inter-isotope determination of ultracold rubidium interactions from three high-precision experiments
Combining the measured binding energies of four of the most weakly bound
rovibrational levels of the Rb molecule with the results of two
other recent high-precision rubidium experiments, we obtain exceptionally
strong constraints on the atomic interaction parameters in a highly model
independent analysis. The comparison of Rb and Rb data, where the
two isotopes are related by a mass scaling procedure, plays a crucial role.
Using the consistent picture of the interactions that thus arises we are led to
predictions for scattering lengths, clock shifts, Feshbach resonance fields and
widths with an unprecedented level of accuracy. To demonstrate this, we predict
two Feshbach resonances in mixed-spin scattering channels at easily accessible
magnetic field strengths, which we expect to play a role in the damping of
coherent spin oscillations
Elastic and inelastic collisions of 6Li in magnetic and optical traps
We use a full coupled channels method to calculate collisional properties of
magnetically or optically trapped ultracold 6Li. The magnetic field dependence
of the s-wave scattering lengths of several mixtures of hyperfine states are
determined, as are the decay rates due to exchange collisions. In one case, we
find Feshbach resonances at B=0.08 T and B=1.98 T. We show that the exact
coupled channels calculation is well approximated over the entire range of
magnetic fields by a simple analytical calculation.Comment: 4 pages revtex including 4 figures, submitted to PR
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