3 research outputs found
Dynamical formation and interaction of bright solitary waves and solitons in the collapse of Bose-Einstein condensates with attractive interactions
We model the dynamics of formation of multiple, long-lived, bright solitary
waves in the collapse of Bose-Einstein condensates with attractive interactions
as studied in the experiment of Cornish et al. [Phys. Rev. Lett. 96 (2006)
170401]. Using both mean-field and quantum field simulation techniques, we find
that while a number of separated wave packets form as observed in the
experiment, they do not have a repulsive \pi phase difference that has been
previously inferred. We observe that the inclusion of quantum fluctuations
causes soliton dynamics to be predominantly repulsive in one dimensional
simulations independent of their initial relative phase. However, indicative
three-dimensional simulations do not support this conclusion and in fact show
that quantum noise has a negative impact on bright solitary wave lifetimes.
Finally, we show that condensate oscillations, after the collapse, may serve to
deduce three-body recombination rates, and that the remnant atom number may
still exceed the critical number for collapse for as long as three seconds
independent of the relative phases of the bright solitary waves.Comment: 14 pages, 5 figure
Orbital Josephson effect and interactions in driven atom condensates on a ring
In a system of ac-driven condensed bosons we study a new type of Josephson
effect occurring between states sharing the same region of space and the same
internal atom structure. We first develop a technique to calculate the long
time dynamics of a driven interacting many-body system. For resonant
frequencies, this dynamics can be shown to derive from an effective
time-independent Hamiltonian which is expressed in terms of standard creation
and annihilation operators. Within the subspace of resonant states, and if the
undriven states are plane waves, a locally repulsive interaction between bosons
translates into an effective attraction. We apply the method to study the
effect of interactions on the coherent ratchet current of an asymmetrically
driven boson system. We find a wealth of dynamical regimes which includes Rabi
oscillations, self-trapping, and chaotic behavior. In the latter case, a full
many-body calculation deviates from the mean-field results by predicting large
quantum fluctuations of the relative particle number.Comment: Published versio
Finite Temperature Models of Bose-Einstein Condensation
The theoretical description of trapped weakly-interacting Bose-Einstein
condensates is characterized by a large number of seemingly very different
approaches which have been developed over the course of time by researchers
with very distinct backgrounds. Newcomers to this field, experimentalists and
young researchers all face a considerable challenge in navigating through the
`maze' of abundant theoretical models, and simple correspondences between
existing approaches are not always very transparent. This Tutorial provides a
generic introduction to such theories, in an attempt to single out common
features and deficiencies of certain `classes of approaches' identified by
their physical content, rather than their particular mathematical
implementation.
This Tutorial is structured in a manner accessible to a non-specialist with a
good working knowledge of quantum mechanics. Although some familiarity with
concepts of quantum field theory would be an advantage, key notions such as the
occupation number representation of second quantization are nonetheless briefly
reviewed. Following a general introduction, the complexity of models is
gradually built up, starting from the basic zero-temperature formalism of the
Gross-Pitaevskii equation. This structure enables readers to probe different
levels of theoretical developments (mean-field, number-conserving and
stochastic) according to their particular needs. In addition to its `training
element', we hope that this Tutorial will prove useful to active researchers in
this field, both in terms of the correspondences made between different
theoretical models, and as a source of reference for existing and developing
finite-temperature theoretical models.Comment: Detailed Review Article on finite temperature theoretical techniques
for studying weakly-interacting atomic Bose-Einstein condensates written at
an elementary level suitable for non-experts in this area (e.g. starting PhD
students). Now includes table of content