Nonlinear Topological Edge States in a non-Hermitian Array of Optical Waveguides Embedded in an Atomic Gas

TL;DR

This paper introduces a tunable array of optical waveguides embedded in atomic gases that exhibits nonlinear topological edge states, bridging non-Hermitian, topological, and nonlinear physics with potential for novel optical functionalities.

Contribution

It generalizes the Rice-Mele Hamiltonian to a nonlinear, non-Hermitian quadrimer array with odd-PT symmetry, enabling control over topological phases and edge states.

Findings

Realization of topologically distinct phases in the waveguide array

Existence of nonlinear topological edge states bifurcating from linear states

Stabilization of nonlinear edge states with added absorption

Abstract

We propose a scheme comprising an array of anisotropic optical waveguides, embedded in a gas of cold atoms, which can be tuned from a Hermitian to an odd-PT -- symmetric configuration through the manipulation of control and assistant laser fields. We show that the system can be controlled by tuning intra -- and inter-cell coupling coefficients, enabling the creation of topologically distinct phases and linear topological edge states. The waveguide array, characterized by a quadrimer primitive cell, allows for implementing transitions between Hermitian and odd-PT -symmetric configurations, broken and unbroken PT -symmetric phases, topologically trivial and nontrivial phases, as well as transitions between linear and nonlinear regimes. The introduced scheme generalizes the Rice-Mele Hamiltonian for a nonlinear non-Hermitian quadrimer array featuring odd-PT symmetry and makes accessible unique phenomena and functionalities that emerge from the interplay of non-Hermiticity, topology, and nonlinearity. We also show that in the presence of nonlinearity the system sustains nonlinear topological edge states bifurcating from the linear topological edge states and the modes without linear limit. Each nonlinear mode represents a doublet of odd-PT -conjugate states. In the broken PT phase, the nonlinear edge states may be effectively stabilized when an additional absorption is introduced into the system.