498 research outputs found
Boojums in Rotating Two-Component Bose-Einstein Condensates
A boojum is a topological defect that can form only on the surface of an
ordered medium such as superfluid He and liquid crystals. We study
theoretically boojums appearing between two phases with different vortex
structures in two-component BECs where the intracomponent interaction is
repulsive in one phase and attractive in the other. The detailed structure of
the boojums is revealed by investigating its density distribution, effective
superflow vorticity and pseudospin texture.Comment: 4 pages, 4 figure
Spin textures in rotating two-component Bose-Einstein condensates
We investigate two kinds of coreless vortices with axisymmetric and
nonaxisymmetric configurations in rotating two-component Bose-Einstein
condensates. Starting from the Gross-Pitaevskii energy functional in a rotating
frame, we derive a nonlinear sigma model generalized to the two-component
condensates. In terms of a pseudospin representation, an axisymmetric vortex
and a nonaxisymmetric one correspond to spin textures referred to as a
"skyrmion" and a "meron-pair", respectively. A variational method is used to
investigate the dependence of the sizes of the stable spin textures on system
parameters, and the optimized variational function is found to reproduce well
the numerical solution. In the SU(2) symmetric case, the optimal skyrmion and
meron-pair are degenerate and transform to each other by a rotation of the
pseudospin. An external rf-field that couples coherently the hyperfine states
of two components breaks the degeneracy in favor of the meron-pair texture due
to an effective transverse pseudomagnetic field. The difference between the
intracomponent and intercomponent interactions yields a longitudinal
pseudomagnetic field and a ferromagnetic or an antiferromagnetic pseudospin
interaction, leading to a meron-pair texture with an anisotropic distribution
of vorticity.Comment: 14 pages, 15 figure
Vortex phase diagram in rotating two-component Bose-Einstein condensates
We investigate the structure of vortex states in rotating two-component
Bose-Einstein condensates with equal intracomponent but varying intercomponent
coupling constants. A phase diagram in the intercomponent-coupling versus
rotation-frequency plane reveals rich equilibrium structures of vortex states.
As the ratio of intercomponent to intracomponent couplings increases, the
interlocked vortex lattices undergo phase transitions from triangular to
square, to double-core lattices, and eventually develop interwoven "serpentine"
vortex sheets with each component made up of chains of singly quantized
vortices.Comment: 4 pages, 4 figures, revtex
Vortex molecules in coherently coupled two-component Bose-Einstein condensates
A vortex molecule is predicted in rotating two-component Bose-Einstein
condensates whose internal hyperfine states are coupled coherently by an
external field. A vortex in one component and that in the other are connected
by a domain wall of the relative phase, constituting a "vortex molecule", which
features a nonaxisymmetric (pseudo)spin texture with a pair of merons. The
binding mechanism of the vortex molecule is discussed based on a generalized
nonlinear sigma model and a variational ansatz. The anisotropy of vortex
molecules is caused by the difference in the scattering lengths, yielding a
distorted vortex-molecule lattice in fast rotating condensates.Comment: 4 pages, 4 figures, greatly revised versio
Non classical velocity statistics in a turbulent atomic Bose Einstein condensate
In a recent experiment Paoletti et al (Phys. Rev. Lett. 101, 154501, 2008)
monitored the motion of tracer particles in turbulent superfluid helium and
inferred that the velocity components do not obey the Gaussian statistics
observed in ordinary turbulence. Motivated by their experiment, we create a
small turbulent state in an atomic Bose-Einstein condensate, which enables us
to compute directly the velocity field, and we find similar non-classical
power-law tails. Our result thus suggests that non-Gaussian turbulent velocity
statistics describe a fundamental property of quantum fluids. We also track the
decay of the vortex tangle in the presence of the thermal cloud.Comment: 10 pages, 3 figure
Quantum Kelvin-Helmholtz instability in phase-separated two-component Bose-Einstein condensates
We theoretically study the Kelvin-Helmholtz instability in phase-separated
two-component Bose-Einstein condensates using the Gross-Pitaevskii and
Bogoliubov-de Gennes models. A flat interface between the two condensates is
shown to deform into sawtooth or Stokes-like waves, leading to the formation of
singly quantized vortices on the peaks and troughs of the waves. This scenario
of interface instability in quantum fluids is quite different from that in
classical fluids.Comment: 5 pages, 4 figure
A Novel Closed-Circular Mitochondrial DNA with Properties of a Replicating Intermediate
Spontaneous Radiation and Amplification of Kelvin Waves on Quantized Vortices in Bose-Einstein Condensates
We propose a different type of Landau instability in trapped Bose-Einstein
condensates by a helically moving environment. In the presence of quantized
vortices, the instability can cause spontaneous radiation and amplification of
Kelvin waves. This study gives a microscopic understanding of the
Donnelly-Glaberson instability which was known as a hydrodynamic instability in
superfluid helium.
The Donnelly-Glaberson instability can be a powerful tool for observing the
dispersion relation of Kelvin waves, vortex reconnections, and quantum
turbulence in atomic Bose-Einstein condensates.Comment: 5 pages, 5 figure
Crossover between Kelvin-Helmholtz and counter-superflow instabilities in two-component Bose-Einstein condensates
Dynamical instabilities at the interface between two Bose--Einstein
condensates that are moving relative to each other are investigated using
mean-field and Bogoliubov analyses. Kelvin--Helmholtz instability is dominant
when the interface thickness is much smaller than the wavelength of the
unstable interface mode, whereas the counter-superflow instability becomes
dominant in the opposite case. These instabilities emerge not only in an
immiscible system but also in a miscible system where an interface is produced
by external potential. Dynamics caused by these instabilities are numerically
demonstrated in rotating trapped condensates.Comment: 10 pages, 9 figure
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