293 research outputs found
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
Scattering hypervolume for ultracold bosons from weak to strong interactions
The elastic scattering properties of three bosons at low energy enter the
many-body description of ultracold Bose gases via the three-body scattering
hypervolume . We study this quantity for identical bosons that interact via
a pairwise finite-range potential. Our calculations cover the regime from
strongly repulsive potentials towards attractive potentials supporting multiple
two-body bound states and are consistent with the few existing predictions for
. We present the first numerical confirmation of the universal predictions
for in the strongly interacting regime, where Efimov physics dominates, for
a local nonzero-range potential. Our findings highlight how is influenced
by three-body quasibound states with strong -wave or -wave
characteristics in the weakly interacting regime.Comment: 13 pages, 8 figure
Strong spin-exchange recombination of three weakly interacting 7Li atoms
We reveal a significant spin-exchange pathway in the three-body recombination process for ultracold lithium-7 atoms near a zero-crossing of the two-body scattering length. This newly discovered recombination pathway involves the exchange of spin between all three atoms, which is not included in many theoretical approaches with restricted spin structure. Taking it into account, our calculation is in excellent agreement with experimental observations. To contrast our findings, we predict the recombination rate around a different zero-crossing without strong spin-exchange effects to be two orders of magnitude smaller, which gives a clear advantage to future many-body experiments in this regime. This work opens new avenues to study elementary reaction processes governed by the spin degree of freedom in ultracold gases
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
The multichannel nature of three-body recombination for ultracold K
We develop a full multichannel spin model in momentum space to investigate
three-body recombination of identical alkali-metal atoms colliding in a
magnetic field. The model combines the exact three-atom spin structure and
realistic pairwise atom-atom interactions. By neglecting the interaction
between two particles when the spectating particle is not in its initial spin
state we arrive at an approximate model. With this approximate model we achieve
excellent agreement with the recent precise measurement of the ground Efimov
resonance position in potassium-39 close to 33.58 G [Chapurin ., Phys.
Rev. Lett. 123, 233402 (2019)]. We analyze the limitations of our approximation
by comparing to the numerical results for the full system and find that it
breaks down for Feshbach resonances at larger magnetic fields in the same spin
channel. There the relevant three-body closed channel thresholds are much
closer to the open channel threshold, which enhances the corresponding
multichannel couplings. Therefore the neglected components of the interaction
should be included for those Feshbach resonances
Development of an enhanced single point milling procedure to screen metalworking cutting fluid performance in terms of tool wear when machining aerospace alloys
Metalworking fluids (MWFs) can greatly improve the machinability of materials and increase cutting tool life. There are a range of MWF products available on the market, however there are very few reliable low cost machining based fluid screening tests which can help select the most suitable candidate. This study developed a novel and rigorous single point milling (SPM) procedure carried out under controlled conditions, which would provide fluid performance differentiation for a range of typical aerospace alloys. The use of a single insert with a controlled geometry reduced machining variance and ensured performance repeatability. Tool life curves were used to determine optimum machining surface speeds for Inconel 718 (In718) of 80 m/min and Ti-6Al-4V (Ti64) of 160 m/min. Carrying out trials using five different cutting fluid products within a controlled tool life window clearly demonstrated that the SPM machining test was able to differentiate performance on both In718 and Ti64 material. Overall a 65% and 53% performance difference in tool life behaviour was observed between the best and worst performing fluids for In718 and Ti64, respectively
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