Edge states and quantum optical high-harmonic generation from topological insulators

TL;DR

This paper explores the quantum optical properties of high-harmonic generation (HHG) in topological insulators, revealing phase-dependent squeezing effects and the influence of system size on nonclassical light generation.

Contribution

It introduces a quantum optical analysis of HHG in topological insulators using the Su-Schrieffer-Heeger model, highlighting phase discrimination and size effects on nonclassical light.

Findings

HHG from topological phases exhibits squeezing at the band-gap frequency.

Harmonic spectra can distinguish topological phases, but squeezing degree depends on system size.

Edge states influence the nonclassical properties of HHG in topological materials.

Abstract

The strong-field process of high-harmonic generation (HHG) has, in recent years, been treated from a quantum optical perspective in the emerging research area of strong-field quantum optics. These investigations show that HHG radiation is, in general, in a nonclassical state of light. However, the quantum optical treatment of HHG from topological nontrivial materials is missing. Here, we aim to address this gap in current knowledge and consider the quantum optical HHG response from the Su-Schrieffer-Heeger model, a finite chain of atoms with both a topologically trivial and nontrivial insulating phase, the latter supporting edge states. We find that HHG from both topological phases is squeezed at the band-gap frequency. Interestingly, while the harmonic spectrum discriminates the two topological phases of the system, the degree of squeezing only discriminates the phases for smaller chain lengths. We attribute this difference to a relative increase in overlap between bulk and edge states in the topological nontrivial phase for smaller systems. Our findings reveal how the strength of dipole couplings governs the nonclassical HHG response and define new research questions on topologically protected generation of quantum light in strong-field physics.