Nonlinear Schroedinger Model Research Articles

An extensive resonant normal form for an arbitrary large Klein–Gordon model

We consider a finite but arbitrarily large Klein-Gordon chain, with periodic boundary conditions. In the limit of small couplings in the nearest neighbor interaction, and small (total or specific) energy, a high order resonant normal form is constructed with estimates uniform in the number of degrees of freedom. In particular, the first order normal form is a generalized discrete nonlinear Schroedinger model, characterized by all-to-all sites coupling with exponentially decaying strength.

Quantum fields on star graphs

We construct canonical quantum fields which propagate on a star graph modeling a quantum wire. The construction uses a deformation of the algebra of canonical commutation relations, encoding the interaction in the vertex of the graph. We discuss in this framework the Casimir effect and derive the correction to the Stefan-Boltzmann law induced by the vertex interaction. We also generalize the algebraic setting for covering systems with integrable bulk interactions and solve the quantum non-linear Schroedinger model on a star graph.

Dynamics of the Bose–Einstein condensation

Bose–Einstein condensation is a very general physical phenomenon which takes place not only in the systems of bosonic atoms, but also in optical wave systems. Many important features of the condensation in such diverse systems can be captured by the nonlinear Schroedinger model. Within this model we develop a statistical description in which the condensate is nonlinearly coupled to wave turbulence described by a kinetic equation. Our focus will be on the strong-condensate regime in which the three-wave interaction replaces the four-wave process operating on the preceding stages of an explosive condensate formation and its initial growth. In the strong-condensate regime, the condensate growth accelerates and becomes quadratic in time. This regime will proceed until the wave dispersion drops below a critical value and the state of dispersionless acoustic turbulence forms.

Power and initial pulse width dependent soliton velocity in ferrite films

Magnetostatic backward volume wave propagation in yttrium–iron–garnet thin films supports soliton formation and propagation, which is modeled by the nonlinear Schroedinger equation. Previous experimental data have shown that the propagation velocity depends both on the initial pulse power and the duration; however, in the nonlinear Schroedinger solution the soliton velocity, or wave number deviation, is a free parameter that is independent of the initial pulse characteristics. It is shown that these dependences on the initial pulse parameters arise simply from the nonlinear nature of the magnetostatic backward volume wave dispersion relation. Moreover, this same dependence is predicted in the nonlinear Schroedinger model, but the deviation in wave number is determined by the initial pulse characteristics and is no longer a free parameter.

Orthogonality and completeness of the Bethe Ansatz eigenstates of the nonlinear Schroedinger model

A rigorous proof is given of the orthogonality and the completeness of the Bethe Ansatz eigenstates of theN-body Hamiltonian of the nonlinear Schroedinger model on a finite interval. The completeness proof is based on ideas of C.N. Yang and C.P. Yang, but their continuity argument at infinite coupling is replaced by operator monotonicity at zero coupling. The orthogonality proof uses the algebraic Bethe Ansatz method or inverse scattering method applied to a lattice approximation introduced by Izergin and Korepin. The latter model is defined in terms of monodromy matrices without writing down an explicit Hamiltonian. It is shown that the eigenfunctions of the transfer matrices for this model converge to the Bethe Ansatz eigenstates of the nonlinear Schroedinger model.

Gelfand-Levitan method for operator fields

The quantum generalization of the Gelfand-Levitan method is presented for the nonlinear Schroedinger model. The basic dispersion relation for operator Jost functions is derived, and the Heisenberg field operator is expressed in terms of scattering-data operators. Construction of Green's functions in the zero-density vacuum is discussed. The four-point function is explicitly calculated from the expression for the field operator and compared with the result of a direct Feynman graph summation. In addition it is proved for any number of particles that the Hamiltonian eigenstates constructed from the quantized scattering data are identical with those previously obtained by means of Bethe's ansatz.