4,884 research outputs found
Small rare gas clusters in soft X-ray pulses
We develop a microscopic model for the interaction of small rare gas clusters
with soft X-ray radiation. It is shown that, while the overall charging of the
clusters is rather low, unexpectedly high atomic charge states can arise due to
charge imbalances inside the cluster. The mechanism does not require unusually
high absorption rates, and the heating can be described by standard inverse
bremsstrahlung formulae.Comment: 4 pages, 4 figure
A Levinson theorem for scattering from a Bose-Einstein condensate
A relation between the number of bound collective excitations of an atomic
Bose-Einstein condensate and the phase shift of elastically scattered atoms is
derived. Within the Bogoliubov model of a weakly interacting Bose gas this
relation is exact and generalises Levinson's theorem. Specific features of the
Bogoliubov model such as complex-energy and continuum bound states are
discussed and a numerical example is given.Comment: 4 pages, 3 figure
Polyatomic trilobite Rydberg molecules in a dense random gas
Trilobites are exotic giant dimers with enormous dipole moments. They consist
of a Rydberg atom and a distant ground-state atom bound together by short-range
electron-neutral attraction. We show that highly polar, polyatomic trilobite
states unexpectedly persist and thrive in a dense ultracold gas of randomly
positioned atoms. This is caused by perturbation-induced quantum scarring and
the localization of electron density on randomly occurring atom clusters. At
certain densities these states also mix with a s-state, overcoming selection
rules that hinder the photoassociation of ordinary trilobites
Polyatomic trilobite Rydberg molecules in a dense random gas
Trilobites are exotic giant dimers with enormous dipole moments. They consist
of a Rydberg atom and a distant ground-state atom bound together by short-range
electron-neutral attraction. We show that highly polar, polyatomic trilobite
states unexpectedly persist and thrive in a dense ultracold gas of randomly
positioned atoms. This is caused by perturbation-induced quantum scarring and
the localization of electron density on randomly occurring atom clusters. At
certain densities these states also mix with a s-state, overcoming selection
rules that hinder the photoassociation of ordinary trilobites
Influence of electron-ion collisions on Coulomb crystallization of ultracold neutral plasmas
While ion heating by elastic electron-ion collisions may be neglected for a
description of the evolution of freely expanding ultracold neutral plasmas, the
situation is different in scenarios where the ions are laser-cooled during the
system evolution. We show that electron-ion collisions in laser-cooled plasmas
influence the ionic temperature, decreasing the degree of correlation
obtainable in such systems. However, taking into account the collisions
increases the ion temperature much less than what would be estimated based on
static plasma clouds neglecting the plasma expansion. The latter leads to both
adiabatic cooling of the ions as well as, more importantly, a rapid decrease of
the collisional heating rate
Switching Exciton Pulses Through Conical Intersections
Exciton pulses transport excitation and entanglement adiabatically through
Rydberg aggregates, assemblies of highly excited light atoms, which are set
into directed motion by resonant dipole-dipole interaction. Here, we
demonstrate the coherent splitting of such pulses as well as the spatial
segregation of electronic excitation and atomic motion. Both mechanisms exploit
local nonadiabatic effects at a conical intersection, turning them from a
decoherence source into an asset. The intersection provides a sensitive knob
controlling the propagation direction and coherence properties of exciton
pulses. The fundamental ideas discussed here have general implications for
excitons on a dynamic network.Comment: Letter with 4 pages and 4 figures. Supplemental material with 4 pages
and 4 figure
Friction as Contrast Mechanism in Heterodyne Force Microscopy
The nondestructive imaging of subsurface structures on the nanometer scale
has been a long-standing desire in both science and industry. A few impressive
images were published so far that demonstrate the general feasibility by
combining ultrasound with an Atomic Force Microscope. From different excitation
schemes, Heterodyne Force Microscopy seems to be the most promising candidate
delivering the highest contrast and resolution. However, the physical contrast
mechanism is unknown, thereby preventing any quantitative analysis of samples.
Here we show that friction at material boundaries within the sample is
responsible for the contrast formation. This result is obtained by performing a
full quantitative analysis, in which we compare our experimentally observed
contrasts with simulations and calculations. Surprisingly, we can rule out all
other generally believed responsible mechanisms, like Rayleigh scattering,
sample (visco)elasticity, damping of the ultrasonic tip motion, and ultrasound
attenuation. Our analytical description paves the way for quantitative
SubSurface-AFM imaging.Comment: 7 pages main paper + 11 pages supplementary material
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