13,660 research outputs found
Vortex macroscopic superpositions in ultracold bosons in a double-well potential
We study macroscopic superpositions in the orbital rather than the spatial
degrees of freedom, in a three-dimensional double-well system. We show that the
ensuing dynamics of interacting excited ultracold bosons, which in general
requires at least eight single-particle modes and Fock
vectors, is described by a surprisingly small set of many-body states. An
initial state with half the atoms in each well, and purposely excited in one of
them, gives rise to the tunneling of axisymmetric and transverse vortex
structures. We show that transverse vortices tunnel orders of magnitude faster
than axisymmetric ones and are therefore more experimentally accessible. The
tunneling process generates macroscopic superpositions only distinguishable by
their orbital properties and within experimentally realistic times.Comment: 9 pages, 6 figure
Volume change of bulk metals and metal clusters due to spin-polarization
The stabilized jellium model (SJM) provides us a method to calculate the
volume changes of different simple metals as a function of the spin
polarization, , of the delocalized valence electrons. Our calculations
show that for bulk metals, the equilibrium Wigner-Seitz (WS) radius, , is always a n increasing function of the polarization i.e., the
volume of a bulk metal always increases as increases, and the rate of
increasing is higher for higher electron density metals. Using the SJM along
with the local spin density approximation, we have also calculated the
equilibrium WS radius, , of spherical jellium clusters, at
which the pressure on the cluster with given numbers of total electrons, ,
and their spin configuration vanishes. Our calculations f or Cs, Na,
and Al clusters show that as a function of behaves
differently depending on whether corresponds to a closed-shell or an
open-shell cluster. For a closed-shell cluster, it is an increasing function of
over the whole range , whereas in open-shell clusters
it has a decreasing behavior over the range , where
is a polarization that the cluster has a configuration consistent
with Hund's first rule. The resu lts show that for all neutral clusters with
ground state spin configuration, , the inequality always holds (self-compression) but, at some
polarization , the inequality changes the direction
(self-expansion). However, the inequality
always holds and the equality is achieved in the limit .Comment: 7 pages, RevTex, 10 figure
Particle density and non-local kinetic energy density functional for two-dimensional harmonically confined Fermi vapors
We evaluate analytically some ground state properties of two-dimensional
harmonically confined Fermi vapors with isotropy and for an arbitrary number of
closed shells. We first derive a differential form of the virial theorem and an
expression for the kinetic energy density in terms of the fermion particle
density and its low-order derivatives. These results allow an explicit
differential equation to be obtained for the particle density. The equation is
third-order, linear and homogeneous. We also obtain a relation between the
turning points of kinetic energy and particle densities, and an expression of
the non-local kinetic energy density functional.Comment: 7 pages, 2 figure
Symmetry breaking and singularity structure in Bose-Einstein condensates
We determine the trajectories of vortex singularities that arise after a
single vortex is broken by a discretely symmetric impulse in the context of
Bose-Einstein condensates in a harmonic trap. The dynamics of these
singularities are analyzed to determine the form of the imprinted motion. We
find that the symmetry-breaking process introduces two effective forces: a
repulsive harmonic force that causes the daughter trajectories to be ejected
from the parent singularity, and a Magnus force that introduces a torque about
the axis of symmetry. For the analytical non-interacting case we find that the
parent singularity is reconstructed from the daughter singularities after one
period of the trapping frequency. The interactions between singularities in the
weakly interacting system do not allow the parent vortex to be reconstructed.
Analytic trajectories were compared to the actual minima of the wavefunction,
showing less 0.5% error for impulse strength of (v=0.00005). We show that these
solutions are valid within the impulse regime for various impulse strengths
using numerical integration of the Gross-Pitaevskii equation. We also show that
the actual duration of the symmetry breaking potential does not significantly
change the dynamics of the system as long as the strength is below (v=0.0005).Comment: 14 pages, 10 figure
Tunneling, self-trapping and manipulation of higher modes of a BEC in a double well
We consider an atomic Bose-Einstein condensate trapped in a symmetric
one-dimensional double well potential in the four-mode approximation and show
that the semiclassical dynamics of the two ground state modes can be strongly
influenced by a macroscopic occupation of the two excited modes. In particular,
the addition of the two excited modes already unveils features related to the
effect of dissipation on the condensate. In general, we find a rich dynamics
that includes Rabi oscillations, a mixed Josephson-Rabi regime, self-trapping,
chaotic behavior, and the existence of fixed points. We investigate how the
dynamics of the atoms in the excited modes can be manipulated by controlling
the atomic populations of the ground states.Comment: 12 pages, 5 figure
- …