122 research outputs found
Coupled eigenmodes in a two-component Bose-Einstein condensate
We have studied the elementary excitations in a two-component Bose-Einstein
condensate. We concentrate on the breathing modes and find the elementary
excitations to possess avoided crossings and regions of coalescing oscillations
where both components of the condensates oscillate with same frequency. For
large repulsive interactions between the condensates, their oscillational modes
tend to decouple due to decreased overlap. A thorough investigation of the
eigenmodes near the avoided crossings is presented.Comment: Replacement, 17 pages, 9 figure
Elementary Excitations of a Bose-Einstein Condensate in an Effective Magnetic Field
We calculate the low energy elementary excitations of a Bose-Einstein
Condensate in an effective magnetic field. The field is created by the
interplay between light beams carrying orbital angular momentum and the trapped
atoms. We examine the role of the homogeneous magnetic field, familiar from
studies of rotating condensates, and also investigate spectra for vector
potentials with a more general radial dependence. We discuss the instabilities
which arise and how these may be manifested.Comment: 8 pages, 4 figure
Slow light in degenerate Fermi gases
We investigate the effect of slow light propagating in a degenerate atomic
Fermi gas. In particular we use slow light with an orbital angular momentum. We
present a microscopic theory for the interplay between light and matter and
show how the slow light can provide an effective magnetic field acting on the
electrically neutral fermions, a direct analogy of the free electron gas in an
uniform magnetic field. As an example we illustrate how the corresponding de
Haas-van Alphen effect can be seen in a neutral gas of fermions.Comment: Slightly updated. Phys. Rev. Lett. 93, 033602 (2004
Filled Landau levels in neutral quantum gases
We consider the signatures of the Integer Quantum Hall Effect in a degenerate
gas of electrically neutral atomic fermions. An effective magnetic field is
achieved by applying two incident light beams with a high orbital angular
momentum. We show how states corresponding to completely filled Landau levels
are obtained and discuss various possibilities to measure the incompressible
nature of the trapped two-dimensional gasComment: Minor corrections. Phys. Rev. A, 053632 (2005). High resolution
figures can be obtained from the author
Polarisation rotation of slow light with orbital angular momentum in ultracold atomic gases
We consider the propagation of slow light with an orbital angular momentum
(OAM) in a moving atomic medium. We have derived a general equation of motion
and applied it in analysing propagation of slow light with an OAM in a rotating
medium, such as a vortex lattice. We have shown that the OAM of slow light
manifests itself in a rotation of the polarisation plane of linearly polarised
light. To extract a pure rotational phase shift, we suggest to measure a
difference in the angle of the polarisation plane rotation by two consecutive
light beams with opposite OAM. The differential angle is
proportional to the rotation frequency of the medium
and the winding number of light, and is inversely proportional to the
group velocity of light. For slow light the angle should
be large enough to be detectable. The effect can be used as a tool for
measuring the rotation frequency of the medium.Comment: 5 pages, 1 figur
Landau levels of cold atoms in non-Abelian gauge fields
The Landau levels of cold atomic gases in non-Abelian gauge fields are
analyzed. In particular we identify effects on the energy spectrum and density
distribution which are purely due to the non-Abelian character of the fields.
We investigate in detail non-Abelian generalizations of both the Landau and the
symmetric gauge. Finally, we discuss how these non-Abelian Landau and symmetric
gauges may be generated by means of realistically feasible lasers in a tripod
scheme.Comment: 13 pages, 9 figure
Effective magnetic fields in degenerate atomic gases induced by light beams with orbital angular momenta
We investigate the influence of two resonant laser beams on the mechanical
properties of degenerate atomic gases. The control and probe beams of light are
considered to have Orbital Angular Momenta (OAM) and act on the three-level
atoms in the Electromagnetically Induced Transparency (EIT) configuration. The
theory is based on the explicit analysis of the quantum dynamics of cold atoms
coupled with two laser beams. Using the adiabatic approximation, we obtain an
effective equation of motion for the atoms driven to the dark state. The
equation contains a vector potential type interaction as well as an effective
trapping potential. The effective magnetic field is shown to be oriented along
the propagation direction of the control and probe beams containing OAM. Its
spatial profile can be controlled by choosing proper laser beams. We
demonstrate how to generate a constant effective magnetic field, as well as a
field exhibiting a radial distance dependence. The resulting effective magnetic
field can be concentrated within a region where the effective trapping
potential holds the atoms. The estimated magnetic length can be considerably
smaller than the size of the atomic cloud.Comment: 11 pages, 5 figures Corrected some mistakes in equation
Measuring topology in a laser-coupled honeycomb lattice: From Chern insulators to topological semi-metals
Ultracold fermions trapped in a honeycomb optical lattice constitute a
versatile setup to experimentally realize the Haldane model [Phys. Rev. Lett.
61, 2015 (1988)]. In this system, a non-uniform synthetic magnetic flux can be
engineered through laser-induced methods, explicitly breaking time-reversal
symmetry. This potentially opens a bulk gap in the energy spectrum, which is
associated with a non-trivial topological order, i.e., a non-zero Chern number.
In this work, we consider the possibility of producing and identifying such a
robust Chern insulator in the laser-coupled honeycomb lattice. We explore a
large parameter space spanned by experimentally controllable parameters and
obtain a variety of phase diagrams, clearly identifying the accessible
topologically non-trivial regimes. We discuss the signatures of Chern
insulators in cold-atom systems, considering available detection methods. We
also highlight the existence of topological semi-metals in this system, which
are gapless phases characterized by non-zero winding numbers, not present in
Haldane's original model.Comment: 30 pages, 12 figures, 4 Appendice
(3+1) Massive Dirac Fermions with Ultracold Atoms in Optical Lattices
We propose the experimental realization of (3+1) relativistic Dirac fermions
using ultracold atoms in a rotating optical lattice or, alternatively, in a
synthetic magnetic field. This approach has the advantage to give mass to the
Dirac fermions by coupling the ultracold atoms to a Bragg pulse. A dimensional
crossover from (3+1) to (2+1) Dirac fermions can be obtained by varying the
anisotropy of the lattice. We also discuss under which conditions the
interatomic potentials give rise to relativistically invariant interactions
among the Dirac fermions
Binary Bose-Einstein Condensate Mixtures in Weakly and Strongly Segregated Phases
We perform a mean-field study of the binary Bose-Einstein condensate mixtures
as a function of the mutual repulsive interaction strength. In the phase
segregated regime, we find that there are two distinct phases: the weakly
segregated phase characterized by a `penetration depth' and the strongly
segregated phase characterized by a healing length. In the weakly segregated
phase the symmetry of the shape of each condensate will not take that of the
trap because of the finite surface tension, but its total density profile still
does. In the strongly segregated phase even the total density profile takes a
different symmetry from that of the trap because of the mutual exclusion of the
condensates. The lower critical condensate-atom number to observe the complete
phase segregation is discussed. A comparison to recent experimental data
suggests that the weakly segregated phase has been observed.Comment: minor change
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