481 research outputs found
Ion induced density bubble in a strongly correlated one dimensional gas
We consider a harmonically trapped Tonks-Girardeau gas of impenetrable bosons
in the presence of a single embedded ion, which is assumed to be tightly
confined in a RF trap. In an ultracold ion-atom collision the ion's charge
induces an electric dipole moment in the atoms which leads to an attractive
potential asymptotically. We treat the ion as a static deformation of
the harmonic trap potential and model its short range interaction with the gas
in the framework of quantum defect theory. The molecular bound states of the
ionic potential are not populated due to the lack of any possible relaxation
process in the Tonks-Girardeau regime. Armed with this knowledge we calculate
the density profile of the gas in the presence of a central ionic impurity and
show that a density \textit{bubble} of the order of a micron occurs around the
ion for typical experimental parameters. From these exact results we show that
an ionic impurity in a Tonks gas can be described using a pseudopotential,
allowing for significantly easier treatment.Comment: Accepted for publication in Physical Review A (Rapid Communications)
A bosonic Josephson junction controlled by a single trapped ion
We theoretically investigate the properties of a double-well bosonic
Josephson junction coupled to a single trapped ion. We find that the coupling
between the wells can be controlled by the internal state of the ion, which can
be used for studying mesoscopic entanglement between the two systems and to
measure their interaction with high precision. As a particular example we
consider a single Rb atom and a small Bose-Einstein condensate
controlled by a single Yb ion. We calculate inter-well coupling
rates reaching hundreds of Hz, while the state dependence amounts to tens of Hz
for plausible values of the currently unknown s-wave scattering length between
the atom and the ion. The analysis shows that it is possible to induce either
the self-trapping or the tunneling regime, depending on the internal state of
the ion. This enables the generation of large scale ion-atomic wavepacket
entanglement within current technology.Comment: 6 pages and 5 figures, including additional material. Accepted for
publication in Phys. Rev. Let
Gyrokinetic studies of core turbulence features in ASDEX Upgrade H-mode plasmas
Gyrokinetic validation studies are crucial in developing confidence in the
model incorporated in numerical simulations and thus improving their predictive
capabilities. As one step in this direction, we simulate an ASDEX Upgrade
discharge with the GENE code, and analyze various fluctuating quantities and
compare them to experimental measurements. The approach taken is the following.
First, linear simulations are performed in order to determine the turbulence
regime. Second, the heat fluxes in nonlinear simulations are matched to
experimental fluxes by varying the logarithmic ion temperature gradient within
the expected experimental error bars. Finally, the dependence of various
quantities with respect to the ion temperature gradient is analyzed in detail.
It is found that density and temperature fluctuations can vary significantly
with small changes in this parameter, thus making comparisons with experiments
very sensitive to uncertainties in the experimental profiles. However,
cross-phases are more robust, indicating that they are better observables for
comparisons between gyrokinetic simulations and experimental measurements
- …