Correspondence between non-Hermitian topology and directional amplification in the presence of disorder

TL;DR

This paper demonstrates that non-Hermitian topological effects, such as directional amplification, remain robust in disordered systems, ensuring their practical applicability in cavity arrays even with strong disorder.

Contribution

It analytically establishes the persistence of non-Hermitian topological effects and directional amplification in disordered systems, extending previous results to more realistic scenarios.

Findings

Directional amplification persists despite disorder.

Perfect non-reciprocity is maintained near the exceptional point.

Exponential growth of forward gain with system size is preserved.

Abstract

In order for non-Hermitian (NH) topological effects to be relevant for practical applications, it is necessary to study disordered systems. In the absence of disorder, certain driven-dissipative cavity arrays with engineered non-local dissipation display directional amplification when associated with a non-trivial winding number of the NH dynamic matrix. In this work, we show analytically that the correspondence between NH topology and directional amplification holds even in the presence of disorder. When a system with non-trivial topology is tuned close to the exceptional point, perfect non-reciprocity (quantified by a vanishing reverse gain) is preserved for arbitrarily strong on-site disorder. For bounded disorder, we derive simple bounds for the probability distribution of the scattering matrix elements. These bounds show that the essential features associated with non-trivial NH topology, namely that the end-to-end forward (reverse) gain grows (is suppressed) exponentially with system size, are preserved in disordered systems. NH topology in cavity arrays is robust and can thus be exploited for practical applications.