Transition radiation by matter-wave solitons in optical lattices

We demonstrate that matter-wave solitary pulses formed from Bose condensed atoms moving inside optical lattices continuously radiate dispersive matter waves with prescribed momentum. Our analytical results for the radiation parameters and the soliton decay rate are found to be in excellent agreement with numerical modelling performed for experimentally relevant parameters.Comment: accepted to PR

Frequency selection by soliton excitation in nondegenerate intracavity downconversion

We show that soliton excitation in intracavity downconversion naturally selects a strictly defined frequency difference between the signal and idler fields. In particular, this phenomenon implies that if the signal has smaller losses than the idler then its frequency is pulled away from the cavity resonance and the idler frequency is pulled towards the resonance and {\em vice versa}. The frequency selection is shown to be closely linked with the relative energy balance between the idler and signal fields.Comment: 5 pages, 3 figures. To appear in Phys Rev Let

Observation of bright polariton solitons in a semiconductor microcavity

Microcavity polaritons are composite half-light half-matter quasi-particles, which have recently been demonstrated to exhibit rich physical properties, such as non-equilibrium Bose-Einstein condensation, parametric scattering and superfluidity. At the same time, polaritons have some important advantages over photons for information processing applications, since their excitonic component leads to weaker diffraction and stronger inter-particle interactions, implying, respectively, tighter localization and lower powers for nonlinear functionality. Here we present the first experimental observations of bright polariton solitons in a strongly coupled semiconductor microcavity. The polariton solitons are shown to be non-diffracting high density wavepackets, that are strongly localised in real space with a corresponding broad spectrum in momentum space. Unlike solitons known in other matter-wave systems such as Bose condensed ultracold atomic gases, they are non-equilibrium and rely on a balance between losses and external pumping. Microcavity polariton solitons are excited on picosecond timescales, and thus have significant benefits for ultrafast switching and transfer of information over their light only counterparts, semiconductor cavity lasers (VCSELs), which have only nanosecond response time

Critical sound attenuation in a diluted Ising system

The field-theoretic description of dynamical critical effects of the influence of disorder on acoustic anomalies near the temperature of the second-order phase transition is considered for three-dimensional Ising-like systems. Calculations of the sound attenuation in pure and dilute Ising-like systems near the critical point are presented. The dynamical scaling function for the critical attenuation coefficient is calculated. The influence of quenched disorder on the asymptotic behaviour of the critical ultrasonic anomalies is discussed.Comment: 12 RevTeX pages, 4 figure

Modulational instability of solitary waves in non-degenerate three-wave mixing: The role of phase symmetries

We show how the analytical approach of Zakharov and Rubenchik [Sov. Phys. JETP {\bf 38}, 494 (1974)] to modulational instability (MI) of solitary waves in the nonlinear Schr\"oedinger equation (NLS) can be generalised for models with two phase symmetries. MI of three-wave parametric spatial solitons due to group velocity dispersion (GVD) is investigated as a typical example of such models. We reveal a new branch of neck instability, which dominates the usual snake type MI found for normal GVD. The resultant nonlinear evolution is thereby qualitatively different from cases with only a single phase symmetry.Comment: 4 pages with figure

Dark Solitons in High Velocity Waveguide Polariton Fluids

We study exciton-polariton nonlinear optical fluids in the high momentum waveguide regime for the first time. We demonstrate the formation of dark solitons with the expected dependence of width on fluid density for both main classes of soliton-forming fluid defects. The results are well described by numerical modeling of the fluid propagation. We deduce a continuous wave nonlinearity more than ten times that on picosecond time scales, arising due to interaction with the exciton reservoir

Modulational instability of bright solitary waves in incoherently coupled nonlinear Schr\"odinger equations

We present a detailed analysis of the modulational instability (MI) of ground-state bright solitary solutions of two incoherently coupled nonlinear Schr\"odinger equations. Varying the relative strength of cross-phase and self-phase effects we show existence and origin of four branches of MI of the two-wave solitary solutions. We give a physical interpretation of our results in terms of the group velocity dispersion (GVD) induced polarization dynamics of spatial solitary waves. In particular, we show that in media with normal GVD spatial symmetry breaking changes to polarization symmetry breaking when the relative strength of the cross-phase modulation exceeds a certain threshold value. The analytical and numerical stability analyses are fully supported by an extensive series of numerical simulations of the full model.Comment: Physical Review E, July, 199

Observation of dipole-mode vector solitons

We report on the first experimental observation of a novel type of optical vector soliton, a {\em dipole-mode soliton}, recently predicted theoretically. We show that these vector solitons can be generated in a photorefractive medium employing two different processes: a phase imprinting, and a symmetry-breaking instability of a vortex-mode vector soliton. The experimental results display remarkable agreement with the theory, and confirm the robust nature of these radially asymmetric two-component solitary waves.Comment: 4 pages, 8 figures; pictures in the PRL version are better qualit

Svortices and the fundamental modes of the "snake instability": Possibility of observation in the gaseous Bose-Einstein Condensate

The connection between quantized vortices and dark solitons in a long and thin, waveguide-like trap geometry is explored in the framework of the non-linear Schr\"odinger equation. Variation of the transverse confinement leads from the quasi-1D regime where solitons are stable to 2D (or 3D) confinement where soliton stripes are subject to a transverse modulational instability known as the ``snake instability''. We present numerical evidence of a regime of intermediate confinement where solitons decay into single, deformed vortices with solitonic properties, also called svortices, rather than vortex pairs as associated with the ``snake'' metaphor. Further relaxing the transverse confinement leads to production of 2 and then 3 vortices, which correlates perfectly with a Bogoliubov-de Gennes stability analysis. The decay of a stationary dark soliton (or, planar node) into a single svortex is predicted to be experimentally observable in a 3D harmonically confined dilute gas Bose-Einstein condensate.Comment: 4 pages, 4 figure

Instabilities of Higher-Order Parametric Solitons. Filamentation versus Coalescence

We investigate stability and dynamics of higher-order solitary waves in quadratic media, which have a central peak and one or more surrounding rings. We show existence of two qualitatively different behaviours. For positive phase mismatch the rings break up into filaments which move radially to initial ring. For sufficient negative mismatches rings are found to coalesce with central peak, forming a single oscillating filament.Comment: 5 pages, 7 figure