## Global existence of solutions to coupled PT-symmetric nonlinear Schrödinger equations

Dmitry E. Pelinovsky, Dmitry A. Zezyulin, Vladimir V. Konotop

We study a system of two coupled nonlinear Schrodinger equations, where one equation includes gain and the other one includes losses. Strengths of the gain and the loss are equal, i.e., the resulting system is parity-time (PT) symmetric. The model includes both linear and nonlinear couplings, such that when all nonlinear coefficients are equal, the system represents the PT-generalization of the Manakov model. In the one-dimensional case, we prove the existence of a global solution to the Cauchy problem in energy space $$H_1$$, such that the $$H_1$$-norm of the global solution may grow in time. In the Manakov case, we show analytically that the $$L_2$$-norm of the global solution is bounded for all times and numerically that the $$H_1$$-norm is also bounded. In the two-dimensional case, we obtain a constraint on the $$L_2$$-norm of the initial data that ensures the existence of a global solution in the energy space $$H_1$$.

http://arxiv.org/abs/1411.2895
Analysis of PDEs (math.AP)

## Supercritical blowup in coupled parity-time-symmetric nonlinear Schrödinger equations

João-Paulo Dias, Mário Figueira, Vladimir V. Konotop, Dmitry A. Zezyulin

We prove finite time supercritical blowup in a parity-time-symmetric system of the two coupled nonlinear Schrodinger (NLS) equations. One of the equations contains gain and the other one contains dissipation such that strengths of the gain and dissipation are equal. We address two cases: in the first model all nonlinear coefficients (i.e. the ones describing self-action and non-linear coupling) correspond to attractive (focusing) nonlinearities, and in the second case the NLS equation with gain has attractive nonlinearity while the NLS equation with dissipation has repulsive (defocusing) nonlinearity and the nonlinear coupling is repulsive, as well. The proofs are based on the virial technique arguments. Several particular cases are also illustrated numerically.

http://arxiv.org/abs/1407.2438
Analysis of PDEs (math.AP); Optics (physics.optics)

## PT-symmetric coupler with a coupling defect: soliton interaction with exceptional point

Yuli V. Bludov, Chao Hang, Guoxiang Huang, Vladimir V. Konotop

We study interaction of a soliton in a parity-time (PT) symmetric coupler which has local perturbation of the coupling constant. Such a defect does not change the PT-symmetry of the system, but locally can achieve the exceptional point. We found that the symmetric solitons after interaction with the defect either transform into breathers or blow up. The dynamics of anti-symmetric solitons is more complex, showing domains of successive broadening of the beam and of the beam splitting in two outwards propagating solitons, in addition to the single breather generation and blow up. All the effects are preserved when the coupling strength in the center of the defect deviates from the exceptional point. If the coupling is strong enough the only observable outcome of the soliton-defect interaction is the generation of the breather.

http://arxiv.org/abs/1405.1829
Optics (physics.optics)

## Stochastic PT-symmetric coupler

Vladimir V. Konotop, Dmitry A. Zezyulin

We introduce a stochastic PT-symmetric coupler, which is based on dual-core waveguides with fluctuating parameters, such that the gain and the losses are exactly balanced in average. We consider different parametric regimes which correspond to the broken and unbroken PT symmetry, as well as to the exceptional point of the underlying deterministic system. We demonstrate that in all the cases the statistically averaged intensity of the field grows. This result holds for either linear or nonlinear coupler and is independent on the type of fluctuations.

http://arxiv.org/abs/1401.6352
Optics (physics.optics)

## Gap solitons in the spin-orbit coupled Bose-Einstein condensates

Yaroslav V. Kartashov, Vladimir V. Konotop, Fatkhulla Kh. Abdullaev

We report a diversity of stable gap solitons in a spin-orbit coupled Bose-Einstein condensate subject to a spatially periodic Zeeman field. It is shown that the solitons, can be classified by the main physical symmetries they obey, i.e. symmetries with respect to parity (P), time (T), and internal degree of freedom, i.e. spin, (C) inversions. The conventional gap and gap-stripe solitons are obtained in lattices with different parameters. It is shown that solitons of the same type but obeying different symmetries can exist in the same lattice at different spatial locations. PT and CPT symmetric solitons have anti-ferromagnetic structure and are characterized respectively by nonzero and zero total magnetizations.

http://arxiv.org/abs/1310.8517
Quantum Gases (cond-mat.quant-gas); Pattern Formation and Solitons (nlin.PS)

## Nonlinear modes in a generalized PT-symmetric discrete nonlinear Schrödinger equation

Dmitry E. Pelinovsky, Dmitry A. Zezyulin, Vladimir V. Konotop

We generalize a finite parity-time (PT-)symmetric network of the discrete nonlinear Schrodinger type and obtain general results on linear stability of the zero equilibrium, on the nonlinear dynamics of the dimer model, as well as on the existence and stability of large-amplitude stationary nonlinear modes. A result of particular importance and novelty is the classification of all possible stationary modes in the limit of large amplitudes. We also discover a new integrable configuration of a PT-symmetric dimer.

http://arxiv.org/abs/1310.5651
Pattern Formation and Solitons (nlin.PS); Dynamical Systems (math.DS)

## Tunable nonlinear PT-symmetric defect modes with an atomic cell

Chao Hang, Dmitry A. Zezyulin, Vladimir V. Konotop, Guoxiang Huang

We propose a scheme of creating a tunable highly nonlinear defect in a one-dimensional photonic crystal. The defect consists of an atomic cell filled in with two isotopes of three-level atoms. The probe-field refractive index of the defect can be made parity-time (PT) symmetric, which is achieved by proper combination of a control field and of Stark shifts induced by a far-off-resonance field. In the PT-symmetric system families of stable nonlinear defect modes can be formed by the probe field.

http://arxiv.org/abs/1309.2839

Optics (physics.optics); Pattern Formation and Solitons (nlin.PS)

## Nonlinear modes and integrals of motion in finite PT-symmetric systems

Dmitry A. Zezyulin, Vladimir V. Konotop

We investigate bifurcations of nonlinear modes in parity-time (PT-) symmetric discrete systems. We consider a general class of nonlinearities allowing for existence of the nonlinear modes and address situations when the underlying linear problem is characterized by the presence of degenerate eigenvalues or exceptional-point singularity. In each of the cases we construct formal expansions for small-amplitude nonlinear modes. We also report a class of nonlinearities allowing for a system to admit one or several integrals of motion, which turn out to be determined by the pseudo-Hermiticity of the nonlinearity.

http://arxiv.org/abs/1306.5286
Pattern Formation and Solitons (nlin.PS)

## Discrete vortex solitons and PT symmetry

Daniel Leykam, Vladimir V. Konotop, Anton S. Desyatnikov

We study the effect of lifting the degeneracy of vortex modes with a PT symmetric defect, using discrete vortices in a circular array of nonlinear waveguides as an example. When the defect is introduced, the degenerate linear vortex modes spontaneously break PT symmetry and acquire complex eigenvalues, but nonlinear propagating modes with real propagation constants can still exist. The stability of nonlinear modes depends on both the magnitude and the sign of the vortex charge, thus PT symmetric systems offer new mechanisms to control discrete vortices.

http://arxiv.org/abs/1301.1052
Optics (physics.optics); Pattern Formation and Solitons (nlin.PS)

## PT-symmetry with a system of three-level atoms

Chao Hang, Guoxiang Huang, Vladimir V. Konotop

We show that a vapor of multilevel atoms driven by far-off resonant laser beams, with possibility of interference of two Raman resonances, is highly efficient for creating parity-time (PT) symmetric profiles of the probe-field refractive index, whose real part is symmetric and imaginary part is anti-symmetric in space. The spatial modulation of the susceptibility is achieved by proper combination of standing-wave strong control fields and of Stark shifts induced by a far-off-resonance laser field. As particular examples we explore a mixture of isotopes of Rubidium atoms and design a PT-symmetric lattice and a parabolic refractive index with a linear imaginary part.

http://arxiv.org/abs/1212.5486

Optics (physics.optics)