Topologically non-trivial Floquet band structure in a system undergoing photonic transitions in the ultra-strong coupling regime

TL;DR

This paper demonstrates that a dynamically-modulated photonic resonator lattice in the ultra-strong coupling regime exhibits topologically non-trivial band gaps and robust edge states, with unique phase transitions not seen in weaker coupling regimes.

Contribution

It reveals the emergence of topological properties and phase transitions in photonic systems operating in the ultra-strong coupling regime, beyond the rotating wave approximation.

Findings

Ultra-strong coupling yields larger bandwidth topological edge modes.

The system exhibits a topological insulator-to-metal phase transition.

Edge states are more robust and less lossy in the ultra-strong coupling regime.

Abstract

We consider a system of dynamically-modulated photonic resonator lattice undergoing photonic transition, and show that in the ultra-strong coupling regime such a lattice can exhibit non-trivial topological properties, including topologically non-trivial band gaps, and the associated topologically-robust one-way edge states. Compared with the same system operating in the regime where the rotating wave approximation is valid, operating the system in the ultra-strong coupling regime results in one-way edge modes that has a larger bandwidth, and is less susceptible to loss. Also, in the ultra-strong coupling regime, the system undergoes a topological insulator-to-metal phase transition as one varies the modulation strength. This phase transition has no counter part in systems satisfying the rotating wave approximation, and its nature is directly related to the non-trivial topology of the quasi-energy space.