4 research outputs found
Self-consistent field theory of polarized BEC: dispersion of collective excitation
We suggest the construction of a set of the quantum hydrodynamics equations
for the Bose-Einstein condensate (BEC), where atoms have the electric dipole
moment. The contribution of the dipole-dipole interactions (DDI) to the Euler
equation is obtained. Quantum equations for the evolution of medium
polarization are derived. Developing mathematical method allows to study effect
of interactions on the evolution of polarization. The developing method can be
applied to various physical systems in which dynamics is affected by the DDI.
Derivation of Gross-Pitaevskii equation for polarized particles from the
quantum hydrodynamics is described. We showed that the Gross-Pitaevskii
equation appears at condition when all dipoles have the same direction which
does not change in time. Comparison of the equation of the electric dipole
evolution with the equation of the magnetization evolution is described.
Dispersion of the collective excitations in the dipolar BEC, either affected or
not affected by the uniform external electric field, is considered using our
method. We show that the evolution of polarization in the BEC leads to the
formation of a novel type of the collective excitations. Detailed description
of the dispersion of collective excitations is presented. We also consider the
process of wave generation in the polarized BEC by means of a monoenergetic
beam of neutral polarized particles. We compute the possibilities of the
generation of Bogoliubov and polarization modes by the dipole beam.Comment: 16 pages, 15 figures. arXiv admin note: substantial text overlap with
arXiv:1106.082
Soliton appearing in boson-fermion mixture at the third order of the interaction radius
In this paper we consider an ultra-cold mixture of boson and fermion atoms on the basis
of quantum hydrodynamics. Small one-dimensional perturbations in such systems are being
analyzed. A possibility is shown for soliton solutions of a new type to appear if the
third order of the interaction radius is taken into account in the analysis of
interactions. A fermion-fermion interaction occurs in explicit form if this approximation
is accepted. The conditions that lead to occurrence of this type of soliton in a mixture
of boson and fermion atoms were investigated. Restrictions on the fermion-fermion
interaction were found that are necessary for this kind of perturbations to appear in the
system. Conditions determining whether perturbances would be a condensed soliton or a
rarefied soliton are shown