46 research outputs found
Collapse and Bose-Einstein condensation in a trapped Bose-gas with negative scattering length
We find that the key features of the evolution and collapse of a trapped Bose
condensate with negative scattering length are predetermined by the particle
flux from the above-condensate cloud to the condensate and by 3-body
recombination of Bose-condensed atoms. The collapse, starting once the number
of Bose-condensed atoms reaches the critical value, ceases and turns to
expansion when the density of the collapsing cloud becomes so high that the
recombination losses dominate over attractive interparticle interaction. As a
result, we obtain a sequence of collapses, each of them followed by dynamic
oscillations of the condensate. In every collapse the 3-body recombination
burns only a part of the condensate, and the number of Bose-condensed atoms
always remains finite. However, it can comparatively slowly decrease after the
collapse, due to the transfer of the condensate particles to the
above-condensate cloud in the course of damping of the condensate oscillations.Comment: 11 pages, 3 figure
Dynamics of dark solitons in elongated Bose-Einstein condensates
We find two types of moving dark soliton textures in elongated Bose-Einstein
condensates: non-stationary kinks and proper dark solitons. The former have a
curved notch region and rapidly decay by emitting phonons and/or proper dark
solitons. The proper moving solitons are characterized by a flat notch region
and we obtain the diagram of their dynamical stability. At finite temperatures
the dynamically stable solitons decay due to the thermodynamic instability. We
develop a theory of their dissipative dynamics and explain experimental data.Comment: ~ 5 pages, 1 figur
Quantum fluctuations in coupled dark solitons in trapped Bose-Einstein condensates
We show that the quantum fluctuations associated with the Bogoliubov
quasiparticle vacuum can be strongly concentrated inside dark solitons in a
trapped Bose Einstein condensate. We identify a finite number of anomalous
modes that are responsible for such quantum phenomena. The fluctuations in
these anomalous modes correspond to the `zero-point' oscillations in coupled
dark solitons.Comment: 4 pages, 3 figure
Lieb Mode in a Quasi One-Dimensional Bose-Einstein Condensate of Atoms
We calculate the dispersion relation associated with a solitary wave in a
quasi-one-dimensional Bose-Einstein condensate of atoms confined in a harmonic,
cylindrical trap in the limit of weak and strong interactions. In both cases,
the dispersion relation is linear for long wavelength excitations and
terminates at the point where the group velocity vanishes. We also calculate
the dispersion relation of sound waves in both limits of weak and strong
coupling.Comment: 4 pages, 2 ps figures, RevTe
Vortex Rings and Lieb Modes in a Cylindrical Bose-Einstein Condensate
We present a calculation of a solitary wave propagating along a cylindrical
Bose-Einstein trap, which is found to be a hybrid of a one-dimensional (1D)
soliton and a three-dimensional (3D) vortex ring. The calculated
energy-momentum dispersion exhibits characteristics similar to those of a mode
proposed sometime ago by Lieb within a 1D model, as well as some rotonlike
features.Comment: 4 pages, 4 figure
Dissipative dynamics of vortex arrays in anisotropic traps
We discuss the dissipative dynamics of vortex arrays in trapped
Bose-condensed gases and analyze the lifetime of the vortices as a function of
trap anisotropy and the temperature. In particular, we distinguish the two
regimes of the dissipative dynamics, depending on the relative strength of the
mutual friction between the vortices and the thermal component, and the
friction of the thermal particles on the trap anisotropy. We study the effects
of heating of the thermal cloud by the escaping vortices on the dynamics of the
system.Comment: RevTeX, 8 pages, 3 eps figure
Dissipative dynamics of a kink state in a Bose-condensed gas
We develop a theory of dissipative dynamics of a kink state in a
finite-temperature Bose-condensed gas. We find that due to the interaction with
the thermal cloud the kink state accelerates towards the velocity of sound and
continuously transforms to the ground-state condensate. We calculate the
life-time of a kink state in a trapped gas and discuss possible experimental
implications.Comment: 4 pages, RevTe
Greying of the Dark Soliton: Depletion in the Anomalous Mode of the Bogoliubov Theory
Quantum depletion from an atomic quasi one dimensional Bose-Einstein
condensate with a dark soliton is studied in a framework of the Bogoliubov
theory. Depletion is dominated by an anomalous mode localized in a notch of the
condensate wave function. Depletion in the anomalous mode requires different
treatment than depletion without anomalous modes. In particular, quantum
depletion in the Bogoliubov vacuum of the anomalous mode is experimentally
irrelevant. A dark soliton is initially prepared in a state with minimal
depletion which is not a stationary state of the Bogoliubov theory. The notch
fills up with incoherent atoms depleted from the condensate. For realistic
parameters the filling time can be as short as 10 ms.Comment: 5 pages, version to appear in Phys.Rev.