365 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
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
Calculations of collisions between cold alkaline earth atoms in a weak laser field
We calculate the light-induced collisional loss of laser-cooled and trapped
magnesium atoms for detunings up to 50 atomic linewidths to the red of the
^1S_0-^1P_1 cooling transition. We evaluate loss rate coefficients due to both
radiative and nonradiative state-changing mechanisms for temperatures at and
below the Doppler cooling temperature. We solve the Schrodinger equation with a
complex potential to represent spontaneous decay, but also give analytic models
for various limits. Vibrational structure due to molecular photoassociation is
present in the trap loss spectrum. Relatively broad structure due to absorption
to the Mg_2 ^1Sigma_u state occurs for detunings larger than about 10 atomic
linewidths. Much sharper structure, especially evident at low temperature,
occurs even at smaller detunings due to of Mg_2 ^1Pi_g absorption, which is
weakly allowed due to relativistic retardation corrections to the forbidden
dipole transition strength. We also perform model studies for the other
alkaline earth species Ca, Sr, and Ba and for Yb, and find similar qualitative
behavior as for Mg.Comment: 20 pages, RevTex, 13 eps figures embedde
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
Peptides from chiral Calpha,alpha-disubstituted glycines : crystallographic characterization of conformation of Calpha-methyl, Calpha-isopropylglycine [(alphaMe)Val] in simple derivatives and model peptides
The mol. and crystal structures of R-L-(aMe)Val-R1 [R = ClCH2CO, R1 = OH; R = Z, R1 = Ala-Ala-OMe (I); R = Ac-Aib-Aib, Z-Aib, R1 = Aib-Aib-OCMe3; (aMe)Val = NHCMe(CHMe2)CO; Z = PhCH2O2C; Aib = NHCMe2CO] were detd. by x-ray diffraction. Tripeptide I adopts a type-I b-turn conformation stabilized by a
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.
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