Momentum-space non-Hermitian skin effect in an exciton-polariton system

TL;DR

This paper demonstrates a novel momentum-space localization effect in exciton-polariton systems caused by an asymmetric imaginary potential, revealing a new way to realize non-Hermitian skin effects without complex lattice engineering.

Contribution

Introducing a simple method to induce skin effects via imaginary potentials in non-lattice systems, experimentally demonstrated with exciton polaritons in a trap.

Findings

Localization depends on pump position relative to the trap center.

Higher polariton densities strengthen the localization.

The effect is absent with concentric pumping.

Abstract

Localization of a macroscopic number of eigenstates on a real-space boundary, known as the non-Hermitian skin effect, is one of the striking topological features emerging from non-Hermiticity. Realizing this effect typically requires periodic (lattice) systems with asymmetry of intersite coupling, which is not readily available in many physical platforms. Instead, it is meticulously engineered, e.g., in photonics, which results in complex structures requiring precise fabrication steps. Here, we propose a simpler mechanism: introducing an asymmetric, purely imaginary potential in a topologically trivial system induces momentum-space localization akin to the skin effect. We experimentally demonstrate this localization using exciton polaritons, hybrid light-matter quasi-particles in a simple engineered `round box' trap, pumped by a laser pump offset from the trap center. The effect disappears if the pump is concentric with the trap. The localization persists and becomes stronger at higher densities of polaritons, when a non-equilibrium Bose-Einstein condensate is formed and the system becomes nonlinear. Our approach offers a new route to realizing skin effects in continuous, non-periodic systems and exploring the interplay of non-Hermiticity, topology, and nonlinearity in macroscopic quantum states.