# Monopole Antimonopole Instability in Non-Hermitian Coupled Waveguides

## TL;DR

This paper explores a non-Hermitian coupled waveguide system with a Berry curvature resembling a hyperbolic monopole, revealing how parameter variations can induce gain, loss, and state switching analogous to monopole charge reversal.

## Contribution

It introduces a novel non-Hermitian waveguide model with a hyperbolic monopole-like Berry curvature, demonstrating monopole-induced gain/loss and non-adiabatic state transitions.

## Key findings

- System exhibits purely imaginary Berry connection.
- Parameter tuning induces net gain or loss.
- System shows non-adiabatic eigenstate switching.

## Abstract

A non-Hermitian coupled waveguide system with periodically varying parameters, in which the Berry curvature is analogous to a hyperbolic magnetic monopole or antimonopole, is investigated. It is shown to have a purely imaginary Berry connection, and is consequently influenced by a geometric multiplier. It is possible for this multiplier to induce net gain or loss in the system, corresponding to the existence of the antimonopole or monopole in parameter space, respectively. For the right choice of parameters, the system will display an apparent non-adiabatic change in behaviour, which implies a switch between the dominant eigenstate in the waveguides, leading to a change in parameter space analogous to a charge reversal of the hyperbolic magnetic monopole.