2,831 research outputs found
Condensates of Strongly-interacting Atoms and Dynamically Generated Dimers
In a system of atoms with large positive scattering length, weakly-bound
diatomic molecules (dimers) are generated dynamically by the strong
interactions between the atoms. If the atoms are modeled by a quantum field
theory with an atom field only, condensates of dimers cannot be described by
the mean-field approximation because there is no field associated with the
dimers. We develop a method for describing dimer condensates in such a model
based on the one-particle-irreducible (1PI) effective action. We construct an
equivalent 1PI effective action that depends not only on the classical atom
field but also on a classical dimer field. The method is illustrated by
applying it to the many-body behavior of bosonic atoms with large scattering
length at zero temperature using an approximation in which the 2-atom amplitude
is treated exactly but irreducible -atom amplitudes for are
neglected. The two 1PI effective actions give identical results for the atom
superfluid phase, but the one with a classical dimer field is much more
convenient for describing the dimer superfluid phase. The results are also
compared with previous work on the Bose gas near a Feshbach resonance.Comment: 10 figure
Linear correlations between 4He trimer and tetramer energies calculated with various realistic 4He potentials
In a previous work [Phys. Rev. A 85, 022502 (2012)] we calculated, with the
use of our Gaussian expansion method for few-body systems, the energy levels
and spatial structure of the 4He trimer and tetramer ground and excited states
using the LM2M2 potential, which has a very strong short-range repulsion. In
this work, we calculate the same quantities using the presently most accurate
4He-4He potential [M. Przybytek et al., Phys. Rev. Lett. 104, 183003 (2010)]
that includes the adiabatic, relativistic, QED and residual retardation
corrections. Contributions of the corrections to the tetramer
ground-(excited-)state energy, -573.90 (-132.70) mK, are found to be,
respectively, -4.13 (-1.52) mK, +9.37 (+3.48) mK, -1.20 (-0.46) mK and +0.16
(+0.07) mK. Further including other realistic 4He potentials, we calculated the
binding energies of the trimer and tetramer ground and excited states, B_3^(0),
B_3^(1), B_4^(0) and B_4^(1), respectively. We found that the four kinds of the
energies for the different potentials exhibit perfect linear correlations
between any two of them over the range of binding energies relevant for 4He
atoms (namely, six types of the generalized Tjon lines are given). The
dimerlike-pair model for 4He clusters, proposed in the previous work, predicts
a simple universal relation B_4^(1)/B_2 =B_3^(0)/B_2 + 2/3, which precisely
explains the correlation between the tetramer excited-state energy and the
trimer ground-state energy, with B_2 being the dimer binding energy.Comment: 10 pages, 3 figures, published version in Phys. Rev. A85, 062505
(2012), Figs. 2, 5, and 6 added, minor changes in the description of the
dimerlike-pair mode
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
When a DNA Triple helix melts: An analog of the Efimov state
The base sequences of DNA contain the genetic code and to decode it a double
helical DNA has to open its base pairs. Recent studies have shown that one can
use a third strand to identify the base sequences without opening the double
helix but by forming a triple helix. It is predicted here that such a three
chain system exhibits the unusual behaviour of the existence of a three chain
bound state in the absence of any two being bound. This phenomenon is analogous
to the Efimov state in three particle quantum mechanics. A scaling theory is
used to justify the Efimov connection. Real space renormalization group (RG),
and exact numerical calculations are used to validate the prediction of a
biological Efimov effect.Comment: Replaced by the (almost) published version, except the word
"curiouser
Dimer-atom scattering between two identical fermions and a third particle
We use the diagrammatic -matrix approach to analyze the three-body
scattering problem between two identical fermions and a third particle (which
could be a different species of fermion or a boson). We calculate the s-wave
dimer-atom scattering length for all mass ratios, and our results exactly match
the results of Petrov. In particular, we list the exact dimer-atom scattering
lengths for all available two-species Fermi-Fermi and Bose-Fermi mixtures. In
addition, unlike that of the equal-mass particles case where the three-body
scattering -matrix decays monotonically as a function of the outgoing
momentum, we show that, after an initial rapid drop, this function changes sign
and becomes negative at large momenta and then decays slowly to zero when the
mass ratio of the fermions to the third particle is higher than a critical
value (around 6.5). As the mass ratio gets higher, modulations of the
-matrix become more apparent with multiple sign changes, related to the
"fall of a particle to the center" phenomenon and to the emergence of
three-body Efimov bound states.Comment: 6 pages, 3 figures, and 2 table
The structure of the atomic helium trimers: Halos and Efimov states
The Faddeev equations for the atomic helium-trimer systems are solved
numerically with high accuracy both for the most sophisticated realistic
potentials available and for simple phenomenological potentials. An efficient
numerical procedure is described. The large-distance asymptotic behavior,
crucial for weakly bound three-body systems, is described almost analytically
for arbitrary potentials. The Efimov effect is especially considered. The
geometric structures of the bound states are quantitatively investigated. The
accuracy of the schematic models and previous computations is comparable, i.e.
within 20% for the spatially extended states and within 40% for the smaller
^4He-trimer ground state.Comment: 32 pages containing 7 figures and 6 table
Strong and radiative decays of the Ds0*(2317) meson in the DK-molecule picture
We consider a possible interpretation of the new charm-strange meson
Ds0*(2317) as a hadronic molecule - a bound state of D and K mesons. Using an
effective Lagrangian approach we calculate the strong Ds0* to Ds pi0 and
radiative Ds0* to Ds* gamma decays. A new impact related to the DK molecular
structure of the Ds0*(2317) meson is that the presence of u(d) quarks in the D
and K mesons gives rise to a direct strong isospin-violating transition Ds0* to
Ds pi0 in addition to the decay mechanism induced by eta-pi0 mixing considered
previously. We show that the direct transition dominates over the eta-pi0
mixing transition in the Ds0* to Ds pi0 decay. Our results for the partial
decay widths are consistent with previous calculations.Comment: 22 pages, 4 figures, accepted for publication in Phys. Rev.
Variational calculation of 4He tetramer ground and excited states using a realistic pair potential
We calculated the 4He trimer and tetramer ground and excited states with the
LM2M2 potential using our Gaussian expansion method (GEM) for ab initio
variational calculations of few-body systems. The method has extensively been
used for a variety of three-, four- and five-body systems in nuclear physics
and exotic atomic/molecular physics. The trimer (tetramer) wave function is
expanded in terms of symmetric three-(four-)body Gaussian basis functions,
ranging from very compact to very diffuse, without assuming any pair
correlation function. Calculated results of the trimer ground and excited
states are in excellent agreement with the literature. Binding energies of the
tetramer ground and excited states are obtained to be 558.98 mK and 127.33 mK
(0.93 mK below the trimer ground state), respectively. Precisely the same shape
of the short-range correlation (r_ij < 4 \AA) in the dimer appear in the ground
and excited states of the trimer and tetramer. Analyzing the asymptotic wave
functions (accurate up to 1000 \AA) of those excited states, we propose a model
which predicts the binding energy of the first excited state of 4He_N measured
from the 4He_{N-1} ground state to be N/2(N-1)xB_2 using dimer binding energy
B_2 only; fit in N=3 and 4 is excellent.Comment: 16 pages, 11 figures, to be published in Phys. Rev. A85 (2012), minor
changes in the description of the dimerlike pair model, references renumbere
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
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