44 research outputs found
Rotonlike instability and pattern formation in spinor Bose-Einstein condensates
We show that metastable phases of an antiferromagnetic spin-1 condensate in a
simple model with pure contact interactions can exhibit a rotonlike minimum in
the excitation spectrum. The introduction of magnetic field gives rise to the
instability of roton modes, which can lead to spontaneous emergence of regular
periodic, polygonal, polyhedral or crystalline patterns, as shown in numerical
simulations within the truncated Wigner approximation. An explanation of the
occurrence of rotonlike instability is given based on the energy and spin
conservation laws
Stability and spatial coherence of nonresonantly pumped exciton-polariton condensates
We investigate the stability and coherence properties of one-dimensional
exciton-polariton condensates under nonresonant pumping. We model the
condensate dynamics using the open-dissipative Gross-Pitaevskii equation. In
the case of spatially homogeneous pumping, we find that the instability of the
steady state leads to significant eduction of the coherence length. We consider
two effects that can lead to the stabilization of the steady state, i.e. the
polariton energy relaxation and the influence of an inhomogeneous pumping
profile. We find that, while the former has little effect on the stability, the
latter is very effective in stabilizing the condensate which results in a large
coherence length.Comment: 7 pages, 5 figure
Spatial solitons and light-induced instabilities in colloidal media
We study nonlinear light propagation in colloidal nanosuspensions. We introduce a novel model for the nonlinear response of colloids
which describes consistently the system in the regimes of low and high light
intensities and low/large concentrations of colloidal particles. We employ
this model to study the light-induced instabilities and demonstrate the
formation of stable spatial solitons as well as the existence of a bistability regime
Soliton interactions and transformations in colloidal media
We study nonlinear light propagation in colloidal suspensions of spherical dielectric nanoparticles. We analyze the existence and properties of one-dimensional self-trapped beams (spatial optical solitons) in such media and demonstrate the existence of
Competition between attractive and repulsive interactions in two-component Bose-Einstein condensates trapped in an optical lattice
We consider effects of inter-species attraction on two-component gap solitons
(GSs) in the binary BEC with intra-species repulsion, trapped in the
one-dimensional optical lattice (OL). Systematic simulations of the coupled
Gross-Pitaevskii equations (GPEs) corroborate an assumption that, because the
effective mass of GSs is negative, the inter-species attraction may
\emph{split} the two-component soliton. Two critical values, and
, of the OL strength () are identified. Two-species GSs
with fully overlapping wave functions are stable in strong lattices (). In an intermediate region, , the
soliton splits into a double-humped state with separated components. Finally,
in weak lattices (%), the splitting generates a pair of
freely moving single-species GSs. We present and explain the dependence of
and on thenumber of atoms (total norm), and on the
relative strength of the competing inter-species attraction and intra-species
repulsion. The splitting of asymmetric solitons, with unequal norms of the two
species, is briefly considered too. It is found and explained that the
splitting threshold grows with the increase of the asymmetry
Light Bullets in Nonlinear Periodically Curved Waveguide Arrays
We predict that stable mobile spatio-temporal solitons can exist in arrays of
periodically curved optical waveguides. We find two-dimensional light bullets
in one-dimensional arrays with harmonic waveguide bending and three-dimensional
bullets in square lattices with helical waveguide bending using variational
formalism. Stability of the light bullet solutions is confirmed by the direct
numerical simulations which show that the light bullets can freely move across
the curved arrays. This mobility property is a distinguishing characteristic
compared to previously considered discrete light bullets which were trapped to
a specific lattice site. These results suggest new possibilities for flexible
spatio-temporal manipulation of optical pulses in photonic lattices.Comment: 7 pages, 4 figure
Crossover from self-defocusing to discrete trapping in nonlinear waveguide arrays
We predict a sharp crossover from nonlinear self-defocusing to discrete
self-trapping of a narrow Gaussian beam with the increase of the refractive
index contrast in a periodic photonic lattice. We demonstrate experimentally
nonlinear discrete localization of light with defocusing nonlinearity by single
site excitation in LiNbO waveguide arrays.Comment: 6 pages, 4 figure
Analytical method for determining quantum well exciton properties in a magnetic field
We develop an analytical approximate method for determining the Bohr radii of Wannier-Mott excitons in thin quantum wells under the influence of magnetic field perpendicular to the quantum well plane. Our hybrid variational-perturbative method allows us to obtain simple closed formulas for exciton binding energies and optical transition rates. We confirm the reliability of our method through exciton-polariton experiments realized in a GaAs/AlAs microcavity with an 8 nm In-x Ga1-xAs quantum well and magnetic field strengths as high as 14 T