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 $^{173}$Yb$^+$, as well as the hyperfine splitting of the $^2P_{3/2}$ state in $^{171}$Yb$^+$. Our results are in agreement with previous measurements but are a factor of 5-9 more precise. For the hyperfine constant $A\left(^2P_{3/2}\right) = 875.4(10)$ 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 $^2P_{3/2}$ state. We find branching fractions for the decay to the $^2D_{3/2}$ state and $^2D_{5/2}$ 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 $^1D\left[5/2\right]_{5/2}$ state in $^{171}$Yb$^+$ to be $A\left(^1D\left[5/2\right]_{5/2}\right) = -107(6)$ 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 $^6$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 $^2S_{1/2}$ ground state, the charge transfer and association rate is found to be at least~10$^{3}$ times smaller than the Langevin collision rate. These results confirm the excellent prospects of $^6$Li--Yb$^+$ for sympathetic cooling and quantum information applications. For ions prepared in the excited electronic states $^2P_{1/2}$, $^2D_{3/2}$ and $^2F_{7/2}$, 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 $\sim$~1--120~mK. The low charge transfer rate for ground state collisions is corroborated by theory, but the $4f$ shell in the Yb$^+$ ion prevents an accurate prediction for the charge transfer rate of the $^2P_{1/2}$, $^2D_{3/2}$ and $^2F_{7/2}$ states. Using \textit{ab initio} methods of quantum chemistry we calculate the atom-ion interaction potentials up to energies of 30$\times 10^3$~cm$^{-1}$, 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 $^6$Li atoms. This species combination has been proposed to be the most suitable system to reach the quantum regime in atom-ion experiments. For $^{174}$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 $^{171}$Yb$^+$, we also find strong rates towards spin polarization. However, relaxation towards the $F=0$ 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 $^{40}$Ca$^+$ ion to Rydberg levels by laser radiation in the vacuum-ultraviolet at 122 nm wavelength. Observed resonances are identified as 3d$^2$D$_{3/2}$ to 51 F, 52 F and 3d$^2$D$_{5/2}$ 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