248 research outputs found
Deviation from one-dimensionality in stationary properties and collisional dynamics of matter-wave solitons
By means of analytical and numerical methods, we study how the residual
three-dimensionality affects dynamics of solitons in an attractive
Bose-Einstein condensate loaded into a cigar-shaped trap. Based on an effective
1D Gross-Pitaevskii equation that includes an additional quintic self-focusing
term, generated by the tight transverse confinement, we find a family of exact
one-soliton solutions and demonstrate stability of the entire family, despite
the possibility of collapse in the 1D equation with the quintic self-focusing
nonlinearity. Simulating collisions between two solitons in the same setting,
we find a critical velocity, , below which merger of identical in-phase
solitons is observed. Dependence of on the strength of the transverse
confinement and number of atoms in the solitons is predicted by means of the
perturbation theory and investigated in direct simulations. Symmetry breaking
in collisions of identical solitons with a nonzero phase difference is also
shown in simulations and qualitatively explained by means of an analytical
approximation.Comment: 10 pages, 7 figure
Non-adiabatic molecular association in thermal gases driven by radio-frequency pulses
The molecular association process in a thermal gas of Rb is
investigated where the effects of the envelope of the radio-frequency field are
taken into account. For experimentally relevant parameters our analysis shows
that with increasing pulse length the corresponding molecular conversion
efficiency exhibits low-frequency interference fringes which are robust under
thermal averaging over a wide range of temperatures. This dynamical
interference phenomenon is attributed to St\"uckelberg phase accumulation
between the low-energy continuum states and the dressed molecular state which
exhibits a shift proportional to the envelope of the radio-frequency pulse
intensity.Comment: 5 pages, 3 figure
Two-dimensional discrete solitons in rotating lattices
We introduce a two-dimensional (2D) discrete nonlinear Schr\"{o}dinger (DNLS)
equation with self-attractive cubic nonlinearity in a rotating reference frame.
The model applies to a Bose-Einstein condensate stirred by a rotating strong
optical lattice, or light propagation in a twisted bundle of nonlinear fibers.
Two species of localized states are constructed: off-axis fundamental solitons
(FSs), placed at distance from the rotation pivot, and on-axis (R=0) vortex
solitons (VSs), with vorticities and 2. At a fixed value of rotation
frequency , a stability interval for the FSs is found in terms of the
lattice coupling constant , , with monotonically
decreasing . VSs with S=1 have a stability interval,
\tilde{C}_{\mathrm{cr}%}^{(S=1)}(\Omega),
which exists for below a certain critical value,
. This implies that the VSs with S=1 are
\emph{destabilized} in the weak-coupling limit by the rotation. On the
contrary, VSs with S=2, that are known to be unstable in the standard DNLS
equation, with , are \emph{stabilized} by the rotation in region
%, with growing as a
function of . Quadrupole and octupole on-axis solitons are considered
too, their stability regions being weakly affected by .Comment: To be published in Physical Review
A quasi-pure Bose-Einstein condensate immersed in a Fermi sea
We report the observation of co-existing Bose-Einstein condensate and Fermi
gas in a magnetic trap. With a very small fraction of thermal atoms, the 7Li
condensate is quasi-pure and in thermal contact with a 6Li Fermi gas. The
lowest common temperature is 0.28 muK = 0.2(1) T_C = 0.2(1) T_F where T_C is
the BEC critical temperature and T_F the Fermi temperature. Behaving as an
ideal gas in the radial trap dimension, the condensate is one-dimensional.Comment: 4 pages, 5 figure
Matter-wave vortices in cigar-shaped and toroidal waveguides
We study vortical states in a Bose-Einstein condensate (BEC) filling a
cigar-shaped trap. An effective one-dimensional (1D) nonpolynomial Schroedinger
equation (NPSE) is derived in this setting, for the models with both repulsive
and attractive inter-atomic interactions. Analytical formulas for the density
profiles are obtained from the NPSE in the case of self-repulsion within the
Thomas-Fermi approximation, and in the case of the self-attraction as exact
solutions (bright solitons). A crucially important ingredient of the analysis
is the comparison of these predictions with direct numerical solutions for the
vortex states in the underlying 3D Gross-Pitaevskii equation (GPE). The
comparison demonstrates that the NPSE provides for a very accurate
approximation, in all the cases, including the prediction of the stability of
the bright solitons and collapse threshold for them. In addition to the
straight cigar-shaped trap, we also consider a torus-shaped configuration. In
that case, we find a threshold for the transition from the axially uniform
state, with the transverse intrinsic vorticity, to a symmetry-breaking pattern,
due to the instability in the self-attractive BEC filling the circular trap.Comment: 6 pages, Physical Review A, in pres
Symbiotic gap and semi-gap solitons in Bose-Einstein condensates
Using the variational approximation and numerical simulations, we study
one-dimensional gap solitons in a binary Bose-Einstein condensate trapped in an
optical-lattice potential. We consider the case of inter-species repulsion,
while the intra-species interaction may be either repulsive or attractive.
Several types of gap solitons are found: symmetric or asymmetric; unsplit or
split, if centers of the components coincide or separate; intra-gap (with both
chemical potentials falling into a single bandgap) or inter-gap, otherwise. In
the case of the intra-species attraction, a smooth transition takes place
between solitons in the semi-infinite gap, the ones in the first finite
bandgap, and semi-gap solitons (with one component in a bandgap and the other
in the semi-infinite gap).Comment: 5 pages, 9 figure
Formation of a Matter-Wave Bright Soliton
We report the production of matter-wave solitons in an ultracold lithium 7
gas. The effective interaction between atoms in a Bose-Einstein condensate is
tuned with a Feshbach resonance from repulsive to attractive before release in
a one-dimensional optical waveguide. Propagation of the soliton without
dispersion over a macroscopic distance of 1.1 mm is observed. A simple
theoretical model explains the stability region of the soliton. These
matter-wave solitons open fascinating possibilities for future applications in
coherent atom optics, atom interferometry and atom transport.Comment: 11 pages, 5 figure
Scattering and Trapping of Nonlinear Schroedinger Solitons in External Potentials
Soliton motion in some external potentials is studied using the nonlinear
Schr\"odinger equation. Solitons are scattered by a potential wall. Solitons
propagate almost freely or are trapped in a periodic potential. The critical
kinetic energy for reflection and trapping is evaluated approximately with a
variational method.Comment: 9 pages, 7 figure
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