Mario Salerno

Gap-Townes solitons and localized excitations in low-dimensional Bose-Einstein condensates in optical lattices

We discuss localized ground states of Bose-Einstein condensates BEC’s in optical lattices with attractive and repulsive three-body interactions in the framework of a quintic nonlinear Schrodinger equation which extends the Gross-Pitaevskii equation to the one-dimensional case. We use both a variational method and a self-consistent approach to show the existence of unstable localized excitations which are similar to Townes solitons of the cubic nonlinear Schrodinger equation in two dimensions. These solutions are shown to be located in the forbidden zones of the band structure, very close to the band edges, separating decaying states from stable localized ones gap solitons fully characterizing their delocalizing transition. In this context the usual gap solitons appear as a mechanism for arresting the collapse in low-dimensional BEC’s in optical lattices with an attractive real three-body interaction. The influence of the imaginary part of the three-body interaction, leading to dissipative effects in gap solitons, and the effect of atoms feeding from the thermal cloud are also discussed. These results may be of interest for both BEC’s in atomic chips and Tonks-Girardeau gas in optical lattices.

Compactons in nonlinear Schrödinger lattices with strong nonlinearity management.

The existence of compactons in the discrete nonlinear Schrödinger equation in the presence of fast periodic time modulations of the nonlinearity is demonstrated. In the averaged discrete nonlinear Schrödinger equation, the resulting effective interwell tunneling depends on the modulation parameters and on the field amplitude. This introduces nonlinear dispersion in the system and can lead to a prototypical realization of single- or multisite stable discrete compactons in nonlinear optical waveguide and Bose-Einstein condensate arrays. These structures can dynamically arise out of Gaussian or compactly supported initial data.

Dark soliton oscillations in Bose–Einstein condensates with multi-body interactions

We consider the dynamics of dark matter wave solitons moving through non-uniform cigar-shaped Bose–Einstein condensates described by the mean field Gross–Pitaevskii equation with generalized nonlinearities, in the case when the condition for the modulation stability of the Bose–Einstein condensate is fulfilled. The analytical expression for the frequency of the oscillations of a deep dark soliton is derived for nonlinearities which are arbitrary functions of the density, while specific results are discussed for the physically relevant case of a cubic–quintic nonlinearity modelling two- and three-body interactions, respectively. Opposite to the usual (cubic) Gross–Pitaevskii equation for which the dark soliton effective mass is known to be constant (equal to 2), in the presence of a cubic–quintic nonlinearity we find that the effective mass depends on the product of the initial density background and the ratio between the coefficient of quintic and cubic nonlinearities, this leading to the interesting possibility of measuring three-body interactions directly from the dark soliton dynamics. A comparison between analytical results and direct numerical simulations of the cubic–quintic Gross–Pitaevskii equation shows good agreement between them which confirms the validity of our approach.

Entangling power of permutation-invariant quantum states

We investigate the von Neumann entanglement entropy as function of the size of a subsystem for permutation invariant ground states in models with finite number of states per site, e.g., in quantum spin models. We demonstrate that the entanglement entropy of n sites in a system of length L generically grows as {sigma} log{sub 2}[2{pi}en(L-n)/L]+C, where {sigma} is the on-site spin and C is a function depending only on magnetization.

Nonreciprocal transmission of microwaves through a long Josephson junction

Nonreciprocal microwave transmission through a long Josephson junction in the flux-flow regime is studied analytically and numerically within the framework of the perturbed sine-Gordon model. We demonstrate that the maximum attenuation of the transmitted power occurs when the direction of the flux flow is opposite to the direction of the microwave propagation. This attenuation is nonreciprocal with respect to the flux-flow direction and can be enhanced by increasing the system length and proper impedance matching of the junction ends to external transmission line.

Landau-Zener tunneling of Bose-Einstein condensates in an optical lattice

In this paper, we develop a theory of the LZ tunneling between the lowest bands of a periodic potential. Our approach reveals the role of modulational instability (MI) on the atom transfer between zones as well as the effect of (partial) suppression of the MI by the lattice acceleration. Our consideration is based on the Gross-Pitaevskii equation, which in the two-zone approximation is reduced to the linearly coupled nonlinear Schrodinger equations. In the presence of nonlinearity, the Bloch states can become unstable and localized states can appear in the gaps between bands (gap-solitons) in which can dramatically affect the atomic transfer rate. The stability properties constitute the main reason of asymmetry of the LZ tunneling

Multidimensional discrete compactons in nonlinear Schrödinger lattices with strong nonlinearity management

The existence of multidimensional lattice compactons in the discrete nonlinear Schr¨odinger equation in the presence of fast periodic time modulations of the nonlinearity is demonstrated. By averaging over the period of the fast modulations, an effective averaged dynamical equation arises with coupling constants involving Bessel functions of the first and zeroth kinds.We show that these terms allow one to solve, at this averaged level, for exact discrete compacton solution configurations in the corresponding stationary equation. We focus on seven types of compacton solutions. Single-site and vortex solutions are found to be always stable in the parametric regimes we examined. Other solutions such as double-site in- and out-of-phase, four-site symmetric and antisymmetric, and a five-site compacton solution are found to have regions of stability and instability in two-dimensional parametric planes, involving variations of the strength of the coupling and of the nonlinearity. We also explore the time evolution of the solutions and compare the dynamics according to the averaged equations with those of the original dynamical system. The possible observation of compactons in Bose-Einstein condensates loaded in a deep two-dimensional optical lattice with interactions modulated periodically in time is also discussed.

Full decoherence induced by local fields in open spin chains with strong boundary couplings

We investigate an open

Josephson Flux-Flow Oscillators in Microwave Fields

XYZ

Split and overlapped binary solitons in optical lattices

spin