192 research outputs found
Collisions of cold magnesium atoms in a weak laser field
We use quantum scattering methods to calculate the light-induced collisional
loss of laser-cooled and trapped magnesium atoms for detunings up to 30 atomic
linewidths to the red of the 1S_0-1P_1 cooling transition. Magnesium has no
hyperfine structure to complicate the theoretical studies. We evaluate both the
radiative and nonradiative mechanisms of trap loss. The radiative escape
mechanism via allowed 1Sigma_u excitation is dominant for more than about one
atomic linewidth detuning. Molecular vibrational structure due to
photoassociative transitions to bound states begins to appear beyond about ten
linewidths detuning.Comment: 4 pages with 3 embedded figure
Quantum degeneracy and interaction effects in spin-polarized Fermi-Bose mixtures
Various features of spin-polarized Fermi gases confined in harmonic traps are
discussed, taking into account possible perspectives of experimental
measurements. The mechanism of the expansion of the gas is explicitly
investigated and compared with the one of an interacting Bose gas. The role of
interactions on the equilibrium and non equilibrium behaviour of the fermionic
component in Fermi-Bose mixtures is discussed. Special emphasis is given to the
case of potassium isotopes mixtures.Comment: 5 pages, 3 figures, revtex, to be published in J. Phys.
Static Properties of Trapped Bose-Fermi Mixed Condensate of Alkali Atoms
Static properties of a bose-fermi mixture of trapped potassium atoms are
studied in terms of coupled Gross-Pitaevskii and Thomas-Fermi equations for
both repulsive and attractive bose-fermi interatomic potentials. Qualitative
estimates are given for solutions of the coupled equations, and the parameter
regions are obtained analytically for the boson-density profile change and for
the boson/fermion phase separation. Especially, the parameter ratio
is found that discriminates the region of the large boson-profile change. These
estimates are applied for numerical results for the potassium atoms and checked
their consistency. It is suggested that a small fraction of fermions could be
trapped without an external potential for the system with an attractive
boson-fermion interaction.Comment: 8 pages,5 figure
Strongly enhanced inelastic collisions in a Bose-Einstein condensate near Feshbach resonances
The properties of Bose-Einstein condensed gases can be strongly altered by
tuning the external magnetic field near a Feshbach resonance. Feshbach
resonances affect elastic collisions and lead to the observed modification of
the scattering length. However, as we report here, this is accompanied by a
strong increase in the rate of inelastic collisions. The observed three-body
loss rate in a sodium Bose-Einstein condensation increased when the scattering
length was tuned to both larger or smaller values than the off-resonant value.
This observation and the maximum measured increase of the loss rate by several
orders of magnitude are not accounted for by theoretical treatments. The strong
losses impose severe limitations for using Feshbach resonances to tune the
properties of Bose-Einstein condensates. A new Feshbach resonance in sodium at
1195 G was observed.Comment: 4 pages, 3 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
Creating massive entanglement of Bose condensed atoms
We propose a direct, coherent coupling scheme that can create massively
entangled states of Bose-Einstein condensed atoms. Our idea is based on an
effective interaction between two atoms from coherent Raman processes through a
(two atom) molecular intermediate state. We compare our scheme with other
recent proposals for generation of massive entanglement of Bose condensed
atoms.Comment: 5 pages, 3 figures; Updated figure 3(a), original was "noisy
A white-light trap for Bose-Einstein condensates
We propose a novel method for trapping Bose-condensed atoms using a
white-light interference fringe. Confinement frequencies of tens of kHz can be
achieved in conjunction with trap depths of only a few micro-K. We estimate
that lifetimes on the order of 10 s can be achieved for small numbers of atoms.
The tight confinement and shallow depth permit tunneling processes to be used
for studying interaction effects and for applications in quantum information.Comment: 10 pages with 3 figure
The density dependence of the transition temperature in a homogenous Bose flui
Transition temperature data obtained as a function of particle density in the
He-Vycor system are compared with recent theoretical calculations for 3D
Bose condensed systems. In the low density dilute Bose gas regime we find, in
agreement with theory, a positive shift in the transition temperature of the
form . At higher densities a maximum is
found in the ratio of for a value of the interaction parameter,
na, that is in agreement with path-integral Monte Carlo calculations.Comment: 4 pages, 3 figure
Observation of p-wave Threshold Law Using Evaporatively Cooled Fermionic Atoms
We have measured independently both s-wave and p-wave cross-dimensional
thermalization rates for ultracold potassium-40 atoms held in a magnetic trap.
These measurements reveal that this fermionic isotope has a large positive
s-wave triplet scattering length in addition to a low temperature p-wave shape
resonance. We have observed directly the p-wave threshold law which, combined
with the Fermi statistics, dramatically suppresses elastic collision rates at
low temperatures. In addition, we present initial evaporative cooling results
that make possible these collision measurements and are a precursor to
achieving quantum degeneracy in this neutral, low-density Fermi system.Comment: 5 pages, 3 figures, 1 tabl
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