Nonlinear modes and symmetries in linearly-coupled pairs of PT-invariant dimers

TL;DR

This paper investigates nonlinear modes and symmetries in coupled PT-symmetric dimers, analyzing their solutions, stability, bifurcations, and dynamical behaviors through analytical and numerical methods.

Contribution

It introduces two new configurations of coupled PT-symmetric dimers and provides analytical solutions, stability analysis, and bifurcation characterization.

Findings

Identification of symmetric and antisymmetric solutions

Observation of bifurcations including symmetry breaking

Unstable modes often lead to blowup or stabilize

Abstract

The subject of the work are pairs of linearly coupled PT-symmetric dimers. Two different settings are introduced, namely, straight-coupled dimers, where each gain site is linearly coupled to one gain and one loss site, and cross-coupled dimers, with each gain site coupled to two lossy ones. The latter pair with equal coupling coefficients represents a "PT-hypersymmetric" quadrimer. We find symmetric and antisymmetric solutions in these systems, chiefly in an analytical form, and explore the existence, stability and dynamical behavior of such solutions by means of numerical methods. We thus identify bifurcations occurring in the systems, including spontaneous symmetry breaking and saddle-center bifurcations. Simulations demonstrate that evolution of unstable branches typically leads to blowup. However, in some cases unstable modes rearrange into stable ones.