31,291 research outputs found
Coherent cross-talk and parametric driving of matter-wave vortices
We show that the interaction between vortices and sound waves in atomic
Bose-Einstein condensates can be elucidated in a double-well trap: with one
vortex in each well, the sound emitted by each precessing vortex can be driven
into the opposing vortex (if of the same polarity). This cross-talk leads to a
periodic exchange of energy between the vortices which is long-range and highly
efficient. The increase in vortex energy (obtained by numerical simulations of
the Gross-Pitaevskii equation) is significant and experimentally observable as
a migration of the vortex to higher density over just a few precession periods.
Similar effects can be controllably engineered by introducing a precessing
localised obstacle into one well as an artificial generator of sound, thereby
demonstrating the parametric driving of energy into a vortex.Comment: 12 pages, 13 figure
Structure formation during the collapse of a dipolar atomic Bose-Einstein condensate
We investigate the collapse of a trapped dipolar Bose-Einstein condensate.
This is performed by numerical simulations of the Gross-Pitaevskii equation and
the novel application of the Thomas-Fermi hydrodynamic equations to collapse.
We observe regimes of both global collapse, where the system evolves to a
highly elongated or flattened state depending on the sign of the dipolar
interaction, and local collapse, which arises due to dynamically unstable
phonon modes and leads to a periodic arrangement of density shells, disks or
stripes. In the adiabatic regime, where ground states are followed, collapse
can occur globally or locally, while in the non-adiabatic regime, where
collapse is initiated suddenly, local collapse commonly occurs. We analyse the
dependence on the dipolar interactions and trap geometry, the length and time
scales for collapse, and relate our findings to recent experiments.Comment: In this version (the published version) we have slightly rewritten
the manuscript in places and have corrected some typos. 15 pages and 13
figure
p-Wave stabilization of three-dimensional Bose-Fermi solitons
We explore bright soliton solutions of ultracold Bose-Fermi gases, showing
that the presence of p-wave interactions can remove the usual collapse
instability and support stable soliton solutions that are global energy minima.
A variational model that incorporates the relevant s- and p-wave interactions
in the system is established analytically and solved numerically to probe the
dependencies of the solitons on key experimental parameters. Under attractive
s-wave interactions, bright solitons exist only as meta-stable states
susceptible to collapse. Remarkably, the presence of repulsive p-wave
interactions alleviates this collapse instability. This dramatically widens the
range of experimentally-achievable soliton solutions and indicates greatly
enhanced robustness. While we focus specifically on the boson-fermion pairing
of 87Rb and 40K, the stabilization inferred by repulsive p-wave interactions
should apply to the wider remit of ultracold Bose-Fermi mixtures.Comment: 9 pages, 6 figure
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