56 research outputs found
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
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
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
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
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
EïŹmov States Embedded in the Three-Body Continuum
We present analytical solutions for the three-body problem with multichannel interactions and identify a class of quasibound Efimov states that can be viewed as three-body Fano-Feshbach resonances. Our method employs a multichannel generalization of the Fermi pseudopotential to model low-energy atom-atom interactions near a magnetically tunable Fano-Feshbach resonance. We discuss the conditions under which quasibound Efimov states may be supported and identify the interaction parameters that limit the lifetimes of these states. We speculate that it may be possible to observe these states using spectroscopic methods, perhaps allowing for the measurement of multiple Efimov resonances
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
Cold three-body collisions in hydrogen-hydrogen-alkali atomic system
We have studied hydrogen-hydrogen-alkali three-body systems in the adiabatic
hyperspherical representation. For the spin-stretched case, there exists a
single H molecular state when is one of the bosonic alkali atoms:
Li, Na, K, Rb and Cs. As a result, the {\em
only} recombination process is the one that leads to formation of H
molecules, H+H+H+H, and such molecules will be stable
against vibrational relaxation. We have calculated the collision rates for
recombination and collision induced dissociation as well as the elastic
cross-sections for H+H collisions up to a temperature of 0.5 K, including
the partial wave contributions from = to . We have also found
that there is just one three-body bound state for such systems for
= and no bound states for higher angular momenta.Comment: 10 pages, 5 figures, 4 table
General Theoretical Description of \u3cem\u3eN\u3c/em\u3e-Body Recombination
Formulas for the cross section and event rate constant describing recombination of N particles are derived in terms of general S-matrix elements. Our result immediately yields the generalized Wigner threshold scaling for the recombination of N bosons. A semianalytical formula encapsulates the overall scaling with energy and scattering length, as well as resonant modifications by the presence of N-body states near the threshold collision energy in the entrance channel. We then apply our model to the case of four-boson recombination into an Efimov trimer and a free atom
Universal three-body physics for fermionic dipoles
A study of the universal physics for three oriented fermionic dipoles in the
hyperspherical adiabatic representation predicts a single long-lived
three-dipole state, which exists in only one three-body symmetry, should form
near a two-dipole resonance. Our analysis reveals the spatial configuration of
the universal state, and the scaling of its binding energy and lifetime with
the strength of the dipolar interaction. In addition, three-body recombination
of fermionic dipoles is found to be important even at ultracold energies. An
additional finding is that an effective long-range repulsion arises between a
dipole and a dipolar dimer that is tunable via dipolar interactions.Comment: 4 pages, 3 figures, 1 tabl
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