552 research outputs found
Multichannel quantum-defect theory for slow atomic collisions
We present a multichannel quantum-defect theory for slow atomic collisions
that takes advantages of the analytic solutions for the long-range potential,
and both the energy and the angular-momentum insensitivities of the short-range
parameters. The theory provides an accurate and complete account of scattering
processes, including shape and Feshbach resonances, in terms of a few
parameters such as the singlet and the triplet scattering lengths. As an
example, results for Na-Na scattering are presented and compared
close-coupling calculations.Comment: 8 pages, 3 figure
Observation of Feshbach-like resonances in collisions between ultracold molecules
We observe magnetically tuned collision resonances for ultracold Cs2
molecules stored in a CO2-laser trap. By magnetically levitating the molecules
against gravity, we precisely measure their magnetic moment. We find an avoided
level crossing which allows us to transfer the molecules into another state. In
the new state, two Feshbach-like collision resonances show up as strong
inelastic loss features. We interpret these resonances as being induced by Cs4
bound states near the molecular scattering continuum. The tunability of the
interactions between molecules opens up novel applications such as controlled
chemical reactions and synthesis of ultracold complex molecules
Creation and manipulation of Feshbach resonances with radio-frequency radiation
We present a simple technique for studying collisions of ultracold atoms in
the presence of a magnetic field and radio-frequency radiation (rf). Resonant
control of scattering properties can be achieved by using rf to couple a
colliding pair of atoms to a bound state. We show, using the example of 6Li,
that in some ranges of rf frequency and magnetic field this can be done without
giving rise to losses. We also show that halo molecules of large spatial extent
require much less rf power than deeply bound states. Another way to exert
resonant control is with a set of rf-coupled bound states, linked to the
colliding pair through the molecular interactions that give rise to
magnetically tunable Feshbach resonances. This was recently demonstrated for
87Rb [Kaufman et al., Phys. Rev. A 80:050701(R), 2009]. We examine the
underlying atomic and molecular physics which made this possible. Lastly, we
consider the control that may be exerted over atomic collisions by placing
atoms in superpositions of Zeeman states, and suggest that it could be useful
where small changes in scattering length are required. We suggest other species
for which rf and magnetic field control could together provide a useful tuning
mechanism.Comment: 21 pages, 8 figures, submitted to New Journal of Physic
Collisional and molecular spectroscopy in an ultracold Bose-Bose mixture
The route toward a Bose-Einstein condensate of dipolar molecules requires the
ability to efficiently associate dimers of different chemical species and
transfer them to the stable rovibrational ground state. Here, we report on
recent spectroscopic measurements of two weakly bound molecular levels and
newly observed narrow d-wave Feshbach resonances. The data are used to improve
the collisional model for the Bose-Bose mixture 41K87Rb, among the most
promising candidates to create a molecular dipolar BEC.Comment: 13 pages, 3 figure
Spectroscopy of Ultracold, Trapped Cesium Feshbach Molecules
We explore the rich internal structure of Cs_2 Feshbach molecules. Pure
ultracold molecular samples are prepared in a CO_2-laser trap, and a multitude
of weakly bound states is populated by elaborate magnetic-field ramping
techniques. Our methods use different Feshbach resonances as input ports and
various internal level crossings for controlled state transfer. We populate
higher partial-wave states of up to eight units of rotational angular momentum
(l-wave states). We investigate the molecular structure by measurements of the
magnetic moments for various states. Avoided level crossings between different
molecular states are characterized through the changes in magnetic moment and
by a Landau-Zener tunneling method. Based on microwave spectroscopy, we present
a precise measurement of the magnetic-field dependent binding energy of the
weakly bound s-wave state that is responsible for the large background
scattering length of Cs. This state is of particular interest because of its
quantum-halo character.Comment: 15 pages, 12 figures, 4 table
Feshbach spectroscopy and analysis of the interaction potentials of ultracold sodium
We have studied magnetic Feshbach resonances in an ultracold sample of Na
prepared in the absolute hyperfine ground state. We report on the observation
of three s-, eight d-, and three g-wave Feshbach resonances, including a more
precise determination of two known s-wave resonances, and one s-wave resonance
at a magnetic field exceeding 200mT. Using a coupled-channels calculation we
have improved the sodium ground-state potentials by taking into account these
new experimental data, and derived values for the scattering lengths. In
addition, a description of the molecular states leading to the Feshbach
resonances in terms of the asymptotic-bound-state model is presented.Comment: 11 pages, 4 figure
Study of Interplanetary Magnetic Field with Ground State Alignment
We demonstrate a new way of studying interplanetary magnetic field -- Ground
State Alignment (GSA). Instead of sending thousands of space probes, GSA allows
magnetic mapping with any ground telescope facilities equipped with
spectropolarimeter. The polarization of spectral lines that are pumped by the
anisotropic radiation from the Sun is influenced by the magnetic realignment,
which happens for magnetic field (<1G). As a result, the linear polarization
becomes an excellent tracer of the embedded magnetic field. The method is
illustrated by our synthetic observations of the Jupiter's Io and comet Halley.
Polarization at each point was constructed according to the local magnetic
field detected by spacecrafts. Both spatial and temporal variations of
turbulent magnetic field can be traced with this technique as well. The
influence of magnetic field on the polarization of scattered light is discussed
in detail. For remote regions like the IBEX ribbons discovered at the boundary
of interstellar medium, GSA provides a unique diagnostics of magnetic field.Comment: 11 pages, 19 figures, published in Astrophysics and Space Scienc
Hydrophilic Polyester Microspheres: Effect of Molecular Weight and Copolymer Composition on Release of BSA
Observation of universality in ultracold 7Li three-body recombination
We report on experimental evidence of universality in ultracold 7Li atoms'
three-body recombination loss in the vicinity of a Feshbach resonance. We
observe a recombination minimum and an Efimov resonance in regions of positive
and negative scattering lengths, respectively, which are connected through the
pole of the Feshbach resonance. Both observed features lie deeply within the
range of validity of the universal theory and we find that the relations
between their properties, i.e. widths and locations, are in an excellent
agreement with the theoretical predictions.Comment: 5 pages, 2 figure
Stimulated Raman adiabatic passage from an atomic to a molecular Bose-Einstein condensate
The process of stimulated Raman adiabatic passage (STIRAP) provides a
possible route for the generation of a coherent molecular Bose-Einstein
condensate (BEC) from an atomic BEC. We analyze this process in a
three-dimensional mean-field theory, including atom-atom interactions and
non-resonant intermediate levels. We find that the process is feasible, but at
larger Rabi frequencies than anticipated from a crude single-mode lossless
analysis, due to two-photon dephasing caused by the atomic interactions. We
then identify optimal strategies in STIRAP allowing one to maintain high
conversion efficiencies with smaller Rabi frequencies and under experimentally
less demanding conditions.Comment: Final published versio
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