103 research outputs found
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
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
Spectroscopy of the <sup>2</sup>S<sub>1/2 </sub>→ <sup>2</sup>P<sub>3/2</sub> transition in Yb II: Isotope shifts, hyperfine splitting, and branching ratios
Prospects of reaching the quantum regime in Li-Yb mixtures
We perform numerical simulations of trapped Yb ions that are
buffer gas cooled by a cold cloud of Li atoms. This species combination has
been suggested to be the most promising for reaching the quantum regime of
interacting atoms and ions in a Paul trap. Treating the atoms and ions
classically, we compute that the collision energy indeed reaches below the
quantum limit for a perfect linear Paul trap. We analyze the effect of
imperfections in the ion trap that cause excess micromotion. We find that the
suppression of excess micromotion required to reach the quantum limit should be
within experimental reach. Indeed, although the requirements are strong, they
are not excessive and lie within reported values in the literature. We analyze
the detection and suppression of excess micromotion in our experimental setup.
Using the obtained experimental parameters in our simulation, we calculate
collision energies that are a factor 2-11 larger than the quantum limit,
indicating that improvements in micromotion detection and compensation are
needed there. We also analyze the buffer-gas cooling of linear and
two-dimensional ion crystals. We find that the energy stored in the eigenmodes
of ion motion may reach 10-100 K after buffer-gas cooling under realistic
experimental circumstances. Interestingly, not all eigenmodes are buffer-gas
cooled to the same energy. Our results show that with modest improvements of
our experiment, studying atom-ion mixtures in the quantum regime is in reach,
allowing for buffer-gas cooling of the trapped ion quantum platform and to
study the occurrence of atom-ion Feshbach resonances.Comment: 39 pages, 22 figure
Experimental setup for studying an ultracold mixture of trapped Yb<sup>+</sup>-<sup>6</sup>Li
Experimental setup for studying an ultracold mixture of trapped Yb-Li
We describe and characterize an experimental apparatus that has been used to
study interactions between ultracold lithium atoms and ytterbium ions. The
preparation of ultracold clouds of Li atoms is described as well as their
subsequent transport and overlap with Yb ions trapped in a Paul trap. We
show how the kinetic energy of the ion after interacting with the atoms can be
obtained by laser spectroscopy. From analyzing the dynamics of the ion in the
absence of atoms, we conclude that background heating, due to electric field
noise, limits attainable buffer gas cooling temperatures. We suspect that this
effect can be mitigated by noise reduction and by increasing the density of the
Li gas, in order to improve its cooling power. Imperfections in the Paul trap
lead to so-called excess micromotion, which poses another limitation to the
buffer gas cooling. We describe in detail how we measure and subsequently
minimize excess micromotion in our setup. We measure the effect of excess
micromotion on attainable ion temperatures after buffer gas cooling and compare
this to molecular dynamics simulations which describe the observed data very
well.Comment: 11 pages and 11 figure
Genomic basis for skin phenotype and cold adaptation in the extinct Steller’s sea cow
Steller’s sea cow, an extinct sirenian and one of the largest Quaternary mammals, was described by Georg Steller in 1741 and eradicated by humans within 27 years. Here, we complement Steller’s descriptions with paleogenomic data from 12 individuals. We identified convergent evolution between Steller’s sea cow and cetaceans but not extant sirenians, suggesting a role of several genes in adaptation to cold aquatic (or marine) environments. Among these are inactivations of lipoxygenase genes, which in humans and mouse models cause ichthyosis, a skin disease characterized by a thick, hyperkeratotic epidermis that recapitulates Steller’s sea cows’ reportedly bark-like skin. We also found that Steller’s sea cows’ abundance was continuously declining for tens of thousands of years before their description, implying that environmental changes also contributed to their extinction
New insights on phylogeography and distribution of painted frogs (Discoglossus) in northern Africa and the Iberian Peninsula
Painted frogs (Discoglossus) contain five to six species of Western Palearctic anurans that are mainly distributed
in allopatry. We here provide the first comprehensive assessment of the phylogeography of the Moroccan species D. scovazzi
and geographically characterize its contact zone with D. pictus in Eastern Morocco. Discoglossus scovazzi shows, in general,
a weak phylogeographic structure across Morocco on the basis of mitochondrial DNA sequences of the cytochrome b gene,
with only populations centered in the Atlas Mountains characterized by the presence of slightly divergent haplotypes. In
eastern Morocco, all populations east of the Moulouya River were clearly assignable to D. pictus. This species was also
found along the Mediterranean coast west of the Moulouya, in the cities of Nador and Melilla, suggesting that not the river
itself but the wide arid valley extending along much of the river (except close to the estuary) acts as a possible distributional
barrier to these frogs. No sympatry of D. scovazzi with D. pictus was observed, and all specimens were concordantly assigned
to either species by DNA sequences of cytochrome b and of the nuclear marker RAG1. Species distribution models of the two
taxa show largely overlapping areas of suitable habitat, and the two species’ niches are significantly more similar than would
be expected given the underlying environmental differences between the regions in which they occur. Comparative data are
also presented from the southern Iberian contact zone of D. galganoi galganoi and D. g. jeanneae. These taxa showed less
clear-cut distributional borders, extensively shared RAG1 haplotypes, and had instances of sympatric occurrence on the basis
of cytochrome b haplotypes, in agreement with the hypothesis of a yet incomplete speciation. In this wide contact zone area
we found mitochondrial sequences containing double peaks in electropherograms, suggesting nuclear pseudogenes or (less
likely) heteroplasmy, possibly related to the ongoing admixture among the lineagesPeer reviewe
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