2,278 research outputs found
Ultracold three-body collisions near overlapping Feshbach resonances
We present a comprehensive collection of ultracold three-body collisions
properties near overlapping Feshbach resonances. Our results incorporate
variations of all scattering lengths and demonstrate novel collisional
behavior, such as atom-molecule interference effects. Taking advantage of the
unique ways in which these collisions reflect Efimov physics, new pathways to
control atomic and molecular losses open up. Further, we show that overlapping
resonances can greatly improve the chances of observing multiple Efimov
features in an ultracold quantum gas for nearly any system.Comment: 4 pages, 3 figures, 1 tabl
Mass Dependence of Ultracold Three-Body Collision Rates
We show that many aspects of ultracold three-body collisions can be
controlled by choosing the mass ratio between the collision partners. In the
ultracold regime, the scattering length dependence of the three-body rates can
be substantially modified from the equal mass results. We demonstrate that the
only non-trivial mass dependence is due solely to Efimov physics. We have
determined the mass dependence of the three-body collision rates for all
heteronuclear systems relevant for two-component atomic gases with resonant
s-wave interspecies interactions, which includes only three-body systems with
two identical bosons or two identical fermions
Energy spectra of small bosonic clusters having a large two-body scattering length
In this work we investigate small clusters of bosons using the hyperspherical
harmonic basis. We consider systems with particles interacting
through a soft inter-particle potential. In order to make contact with a real
system, we use an attractive gaussian potential that reproduces the values of
the dimer binding energy and the atom-atom scattering length obtained with one
of the most widely used He-He interactions, the LM2M2 potential. The
intensity of the potential is varied in order to explore the clusters' spectra
in different regions with large positive and large negative values of the
two-body scattering length. In addition, we include a repulsive three-body
force to reproduce the trimer binding energy. With this model, consisting in
the sum of a two- and three-body potential, we have calculated the spectrum of
the four, five and six particle systems. In all the region explored, we have
found that these systems present two bound states, one deep and one shallow
close to the threshold. Some universal relations between the energy
levels are extracted; in particular, we have estimated the universal ratios
between thresholds of the three-, four-, and five-particle continuum using the
two-body gaussia
The Efimov effect for three interacting bosonic dipoles
Three oriented bosonic dipoles are treated using the hyperspherical adiabatic
representation, providing numerical evidence that the Efimov effect persists
near a two-dipole resonance and in a system where angular momentum is not
conserved. Our results further show that the Efimov features in scattering
observables become universal, with a known three-body parameter, i.e. the
resonance energies depend only on the two-body physics, which also has
implications for the universal spectrum of the four-dipole problem. Moreover,
the Efimov states should be long-lived, which is favorable for their creation
and manipulation in ultracold dipolar gases. Finally, deeply-bound two-dipole
states are shown to be relatively stable against collisions with a third
dipole, owing to the emergence of a repulsive interaction originating in the
angular momentum nonconservation for this system.Comment: 4 pages, 2 figures, 1 tabl
Origin of the Three-body Parameter Universality in Efimov Physics
In recent years extensive theoretical and experimental studies of universal
few-body physics have led to advances in our understanding of universal Efimov
physics [1]. The Efimov effect, once considered a mysterious and esoteric
effect, is today a reality that many experiments in ultracold quantum gases
have successfully observed and continued to explore [2-14]. Whereas theory was
the driving force behind our understanding of Efimov physics for decades,
recent experiments have contributed an unexpected discovery. Specifically,
measurements have found that the so-called three-body parameter determining
several properties of the system is universal, even though fundamental
assumptions in the theory of the Efimov effect suggest that it should be a
variable property that depends on the precise details of the short-range two-
and three-body interactions. The present Letter resolves this apparent
contradiction by elucidating unanticipated implications of the two-body
interactions. Our study shows that the three-body parameter universality
emerges because a universal effective barrier in the three-body potentials
prevents the three particles from simultaneously getting close to each other.
Our results also show limitations on this universality, as it is more likely to
occur for neutral atoms and less likely to extend to light nuclei.Comment: 11 pages; 9 figures. Includes Supplementary Materia
Ultracold atom-molecule collisions with fermionic atoms
Elastic and inelastic properties of weakly bound s- and p-wave molecules of
fermionic atoms that collide with a third atom are investigated. Analysis of
calculated collisional properties of s-wave dimers of fermions in different
spin states permit us to compare and highlight the physical mechanisms that
determine the stability of s-wave and p-wave molecules. In contrast to s-wave
molecules, the collisional properties of p-wave molecules are found to be
largely insensitive to variations of the p-wave scattering length and that
these collisions will usually result in short molecular lifetimes. We also
discuss the importance of this result for both theories and experiments
involving degenerate Fermi gases.Comment: 6 pages, 2 figure
Production of three-body Efimov molecules in an optical lattice
We study the possibility of associating meta-stable Efimov trimers from three
free Bose atoms in a tight trap realised, for instance, via an optical lattice
site or a microchip. The suggested scheme for the production of these molecules
is based on magnetically tunable Feshbach resonances and takes advantage of the
Efimov effect in three-body energy spectra. Our predictions on the energy
levels and wave functions of three pairwise interacting 85Rb atoms rely upon
exact solutions of the Faddeev equations and include the tightly confining
potential of an isotropic harmonic atom trap. The magnetic field dependence of
these energy levels indicates that it is the lowest energetic Efimov trimer
state that can be associated in an adiabatic sweep of the field strength. We
show that the binding energies and spatial extents of the trimer molecules
produced are comparable, in their magnitudes, to those of the associated
diatomic Feshbach molecule. The three-body molecular state follows Efimov's
scenario when the pairwise attraction of the atoms is strengthened by tuning
the magnetic field strength.Comment: 21 pages, 8 figures (final version
Limits on Universality in Ultracold Three-Boson Recombination
The recombination rate for three identical bosons has been calculated to test
the limits of its universal behavior. It has been obtained for several
different collision energies and scattering lengths (a) up to 10^5 a.u., giving
rates that vary over 15 orders of magnitude. We find that universal behavior is
limited to the threshold region characterized by E lesssim
hbar^2/(2mu_{12}a^2), where E is the total energy and mu_{12} is the two-body
reduced mass. The analytically predicted infinite series of resonance peaks and
interference minima is truncated to no more than three of each for typical
experimental parameters.Comment: 4 pages, 3 figure
Few-body physics in effective field theory
Effective Field Theory (EFT) provides a powerful framework that exploits a
separation of scales in physical systems to perform systematically improvable,
model-independent calculations. Particularly interesting are few-body systems
with short-range interactions and large two-body scattering length. Such
systems display remarkable universal features. In systems with more than two
particles, a three-body force with limit cycle behavior is required for
consistent renormalization already at leading order. We will review this EFT
and some of its applications in the physics of cold atoms and nuclear physics.
In particular, we will discuss the possibility of an infrared limit cycle in
QCD. Recent extensions of the EFT approach to the four-body system and N-boson
droplets in two spatial dimensions will also be addressed.Comment: 10 pages, 5 figures, Proceedings of the INT Workshop on "Nuclear
Forces and the Quantum Many-Body Problem", Oct. 200
- âŠ