Ultrafast Non-Hermitian Skin Effect

TL;DR

This paper demonstrates the creation and measurement of ultrafast topological non-Hermitian skin modes within a semiconductor laser cavity, revealing new topologically protected states of light in time with potential for advanced applications.

Contribution

It introduces a novel method to generate and observe ultrafast topological skin modes in time-varying laser systems, combining experimental and numerical analysis.

Findings

Measured skin modes with 583 fs FWHM

Demonstrated tuning of skin modes via external bias

Revealed topological protection of field fluctuations

Abstract

Topological phases of matter commonly feature protected states at their boundaries. Transferring this protection to time-metamaterials is extremely challenging, as it requires the generation of an abrupt interface between two topologically distinct bulks. Here, we realize and measure an ultrafast topological non-Hermitian skin mode bound to an interface circulating within the cavity of a fast-gain semiconductor laser. The nonlinear stationary state generated in such devices features a jump in the instantaneous frequency. We show that this discontinuity gives rise to a topological interface for the field fluctuations in the system. Using direct intensity sampling, we experimentally measure the skin modes and their positioning at the frequency jump of the stationary state. Analysis of these isolated modes reveals an ultrashort full-width at half-maximum of 583 $\pm$ 16 fs. Furthermore, we show that we can tune the shape and relative timing shift of the skin modes via external bias modulation. Finally, both numerical and experimental analysis of the noise in the system reveal that field fluctuations are funneled into the topological interface. Our findings reveal a new way to generate topologically protected states of light in time, which paves the way for novel time-varying physics as well as metrological applications.