Doubly topological harmonic generation

TL;DR

This paper demonstrates a novel nonlinear interaction between two topological states in a hybrid plasmonic-photonic system, enabling doubly protected nonlinear photonic devices with potential quantum information applications.

Contribution

It experimentally realizes frequency-doubled topological states with unique spin-momentum locking via nonlinear phase matching in a hybrid topological insulator.

Findings

Achieved phase-matched nonlinear interaction between two topological states.

Observed spin-momentum locking in the phase matching process.

Proposed implications for robust quantum photonic devices.

Abstract

The proposition that band geometry alone can protect optical states against disorder has proven not merely theoretically elegant but experimentally incontrovertible. A key attribute of photonic topological systems is their capacity to simultaneously possess high-intensity excitations at multiple distinct frequencies that are confined to the same topological interface. However, exploiting this freedom to protect the interaction between at least two topological states has remained an open experimental challenge. Here, we report an interaction between two topological states, with one being precisely frequency-doubled to the other, supported in a hybrid plasmonic and photonic topological insulator via nonlinear phase matching. We find that the phase matching inherits a unique spin-momentum locking unseen in conventional nonlinear systems. This ability to bring two topological states into phase-matched nonlinear interaction at a single interface sets the stage for a new class of doubly protected nonlinear photonic devices, potentially finding implications in generating entangled photon pairs with enhanced resilience and robustness for secure quantum information technology.