93 research outputs found
Heteronuclear collisions between laser-cooled metastable neon atoms
We investigate heteronuclear collisions in isotope mixtures of laser-cooled
metastable 3P2 neon. Experiments are performed with spin-polarized atoms in a
magnetic trap for all two-isotope combinations of the stable neon isotopes
20Ne, 21Ne, and 22Ne. We determine the rate coefficients for heteronuclear
ionizing collisions to beta_{21,20}=(3.9+/-2.7) x 10^{-11} cm^3/s,
beta_{22,20}=(2.6+/-0.7) x 10^{-11} cm^3/s, and beta_{21,22}=(3.9+/-1.9) x
10^{-11} cm^3/s. We also study heteronuclear elastic collision processes and
give upper bounds for heteronuclear thermal relaxation cross sections. This
work significantly extends the limited available experimental data on
heteronuclear ionizing collisions for laser-cooled atoms involving one or more
rare gas atoms in a metastable state
Observation of Interactions between Trapped Ions and Ultracold Rydberg Atoms
We report on the observation of interactions between ultracold Rydberg atoms
and ions in a Paul trap. The rate of observed inelastic collisions, which
manifest themselves as charge transfer between the Rydberg atoms and ions,
exceeds that of Langevin collisions for ground state atoms by about three
orders of magnitude. This indicates a huge increase in interaction strength. We
study the effect of the vacant Paul trap's electric fields on the Rydberg
excitation spectra. To quantitatively describe the exhibited shape of the ion
loss spectra, we need to include the ion-induced Stark shift on the Rydberg
atoms. Furthermore, we demonstrate Rydberg excitation on a dipole-forbidden
transition with the aid of the electric field of a single trapped ion. Our
results confirm that interactions between ultracold atoms and trapped ions can
be controlled by laser coupling to Rydberg states. Adding dynamic Rydberg
dressing may allow for the creation of spin-spin interactions between atoms and
ions, and the elimination of collisional heating due to ionic micromotion in
atom-ion mixtures.Comment: 7 pages, 5 figures, including appendices. Note that the title has
been changed in version
Spectroscopy of the ^2S_{1/2} \rightarrow\,^2P_{3/2} transition in Yb II: Isotope shifts, hyperfine splitting and branching ratios
We report on spectroscopic results on the ^2S_{1/2} \rightarrow\,^2P_{3/2}
transition in single trapped Yb ions. We measure the isotope shifts for all
stable Yb isotopes except Yb, as well as the hyperfine
splitting of the state in Yb. Our results are in
agreement with previous measurements but are a factor of 5-9 more precise. For
the hyperfine constant MHz our results
also agree with previous measurements but deviate significantly from
theoretical predictions. We present experimental results on the branching
ratios for the decay of the state. We find branching fractions for
the decay to the state and state of 0.17(1)% and
1.08(5)%, respectively, in rough agreement with theoretical predictions.
Furthermore, we measured the isotope shifts of the ^2F_{7/2}
\rightarrow\,^1D\left[5/2\right]_{5/2} transition and determine the hyperfine
structure constant for the state in Yb
to be MHz.Comment: 6 pages, 4 figure
Observation of collisions between cold Li atoms and Yb ions
We report on the observation of cold collisions between Li atoms and
Yb ions. This combination of species has recently been proposed as the most
suitable for reaching the quantum limit in hybrid atom-ion systems, due to its
large mass ratio. For atoms and ions prepared in the ground state,
the charge transfer and association rate is found to be at least~10 times
smaller than the Langevin collision rate. These results confirm the excellent
prospects of Li--Yb for sympathetic cooling and quantum information
applications. For ions prepared in the excited electronic states ,
and , we find that the reaction rate is dominated by
charge transfer and does not depend on the ionic isotope nor the collision
energy in the range ~1--120~mK. The low charge transfer rate for ground
state collisions is corroborated by theory, but the shell in the Yb
ion prevents an accurate prediction for the charge transfer rate of the
, and states. Using \textit{ab initio}
methods of quantum chemistry we calculate the atom-ion interaction potentials
up to energies of 30~cm, and use these to give qualitative
explanations of the observed rates.Comment: 8 pages, 7 figures (including appendices
Dynamics of a single ion spin impurity in a spin-polarized atomic bath
We report on observations of spin dynamics in single Yb ions immersed in
a cold cloud of spin-polarized Li atoms. This species combination has been
proposed to be the most suitable system to reach the quantum regime in atom-ion
experiments. For Yb, we find that the atomic bath polarizes the
spin of the ion by 93(4)\,\% after a few Langevin collisions, pointing to
strong spin-exchange rates. For the hyperfine ground states of Yb,
we also find strong rates towards spin polarization. However, relaxation
towards the ground state occurs after 7.7(1.5) Langevin collisions. We
investigate spin impurity atoms as possible source of apparent spin-relaxation
leading us to interpret the observed spin-relaxation rates as an upper limit.
Using ab initio electronic structure and quantum scattering calculations, we
explain the observed rates and analyze their implications for the possible
observation of Feshbach resonances between atoms and ions once the quantum
regime is reached.Comment: 10 pages, 11 figure
Trapped ions in Rydberg-dressed atomic gases
We theoretically study trapped ions that are immersed in an ultracold gas of
Rydberg-dressed atoms. By off-resonant coupling on a dipole-forbidden
transition, the adiabatic atom-ion potential can be made repulsive. We study
the energy exchange between the atoms and a single trapped ion and find that
Langevin collisions are inhibited in the ultracold regime for these repulsive
interactions. Therefore, the proposed system avoids recently observed ion
heating in hybrid atom-ion systems caused by coupling to the ion's radio
frequency trapping field and retains ultracold temperatures even in the
presence of excess micromotion.Comment: 9 pages, 5 figures including appendice
Rydberg excitation of a single trapped ion
We demonstrate excitation of a single trapped cold Ca ion to
Rydberg levels by laser radiation in the vacuum-ultraviolet at 122 nm
wavelength. Observed resonances are identified as 3dD to 51 F, 52 F
and 3dD to 64F. We model the lineshape and our results imply a
large state-dependent coupling to the trapping potential. Rydberg ions are of
great interest for future applications in quantum computing and simulation, in
which large dipolar interactions are combined with the superb experimental
control offered by Paul traps.Comment: 4 pages, 3 figure
KNEE JOINT BIOMECHANICS UNDER SYSTEMATICALLY INCREASED LOADING CONDITIONS IN RUNNING
The purpose of this study was to identify the general and individual biomechanical response to increased vertical loading with a particular emphasis on the knee joint in running. Biomechanical analysis was performed in three different loading conditions (100%, 110%, 120% body weight) by means of a standard inverse dynamics procedure using a Vicon Nexus system and an instrumented treadmill. Increased vertical loading was accompanied by increased peak internal knee abduction moments and a small increase (0.6°) of knee adduction angles. Two adaptation mechanisms could be identified, differing with respect to the increase of peak vertical GRF and abduction moments. It might be that runners aim at maintaining their habitual joint motion path, choosing a strategy that corresponds to their capacities to resist additional external loads
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