2 research outputs found
Dark-bright solitons in Bose-Einstein condensates at finite temperatures
We study the dynamics of dark-bright solitons in binary mixtures of Bose
gases at finite temperature using a system of two coupled dissipative
Gross-Pitaevskii equations. We develop a perturbation theory for the
two-component system to derive an equation of motion for the soliton centers
and identify different temperature-dependent damping regimes. We show that the
effect of the bright ("filling") soliton component is to partially stabilize
"bare" dark solitons against temperature-induced dissipation, thus providing
longer lifetimes. We also study analytically thermal effects on dark-bright
soliton "molecules" (i.e., two in- and out-of-phase dark-bright solitons),
showing that they undergo expanding oscillations while interacting. Our
analytical findings are in good agreement with results obtained via a
Bogoliubov-de Gennes analysis and direct numerical simulations.Comment: 24 pages, 13 figures, to appear in New J. Phy
Grey solitons in a strongly interacting superfluid Fermi Gas
The Bardeen-Cooper-Schrieffer to Bose-Einstein condensate (BCS to BEC)
crossover problem is solved for stationary grey solitons via the Boguliubov-de
Gennes equations at zero temperature. These \emph{crossover solitons} exhibit a
localized notch in the gap and a characteristic phase difference across the
notch for all interaction strengths, from BEC to BCS regimes. However, they do
not follow the well-known Josephson-like sinusoidal relationship between
velocity and phase difference except in the far BEC limit: at unitary the
velocity has a nearly linear dependence on phase difference over an extended
range. For fixed phase difference the soliton is of nearly constant depth from
the BEC limit to unitarity and then grows progressively shallower into the BCS
limit, and on the BCS side Friedel oscillations are apparent in both gap
amplitude and phase. The crossover soliton appears fundamentally in the gap; we
show, however, that the density closely follows the gap, and the soliton is
therefore observable. We develop an approximate power law relationship to
express this fact: the density of grey crossover solitons varies as the square
of the gap amplitude in the BEC limit and a power of about 1.5 at unitarity.Comment: 10 pages, 6 figures, part of New Journal of Physics focus issue
"Strongly Correlated Quantum Fluids: From Ultracold Quantum Gases to QCD
Plasmas," in pres