Nonlinear Photonic Tripartite Phase

TL;DR

This study demonstrates that Kerr nonlinearity in a quasiperiodic photonic lattice enables selective access to a critical phase where localized, critical, and extended states coexist, revealing a state-dependent nonlinear response.

Contribution

The paper experimentally realizes a tripartite phase in a nonlinear quasiperiodic photonic system and shows how nonlinearity enables state-selective control over different transport regimes.

Findings

Weak nonlinearity drives localized states into the critical window.

Stronger nonlinearity restores localization in low-energy states.

Critical, extended, and high-energy localized states exhibit different nonlinear evolutions.

Abstract

Anderson localization is usually understood as a transition between extended and localized phases, with criticality confined to a single mobility edge. Recent advances predict that quasiperiodic systems can instead host a finite critical window bounded by mobility edges, in which localized, critical and extended states coexist. Yet both the experimental realization of this regime and whether interactions can provide controlled access to it remain unknown. Here, we realize such a tripartite phase in a nonlinear quasiperiodic photonic lattice and show that Kerr nonlinearity, acting as an effective interaction, enables state-selective access to the critical window. By tracking wavepacket dynamics, we distinguish localized, critical and extended transport regimes and uncover a state-selective response: rather than simply reinforcing localization through self-trapping, weak nonlinearity drives low-energy localized states into the critical window, whereas stronger nonlinearity restores localization. By contrast, critical, extended and high-energy localized states evolve monotonically towards self-trapped behaviour. Our results reveal a state-selective mechanism by which interactions provide controlled access to a pre-existing critical window in quasiperiodic systems.