Photonic Floquet Topological Insulator in an Atomic Ensemble

TL;DR

This paper demonstrates a photonic Floquet topological insulator in atomic vapor using nonlinear susceptibilities, showing controllable edge states and Dirac cone formation influenced by nonlinear effects.

Contribution

It introduces a novel method to realize and control PFTI in atomic vapor through nonlinear susceptibilities and interference of coupling fields.

Findings

Dirac cones can be formed and manipulated via nonlinear susceptibilities.

Edge states enable unscattered beam propagation along the lattice edges.

Nonlinear susceptibilities can turn the PFTI on or off.

Abstract

We demonstrate the photonic Floquet topological insulator (PFTI) in an atomic vapor with nonlinear susceptibilities. The interference of three coupling fields splits the energy levels periodically to form a periodic refractive index structure with honeycomb symmetry that can be adjusted by the choice of frequency detunings and intensities of the coupling fields, which all affect the appearance of Dirac cones in the momentum space. When the honeycomb lattice sites are helically ordered along the propagation direction, we obtain a PFTI in the atomic vapor in which an obliquely incident beam moves along the zigzag edge without scattering energy into the PFTI, due to the confinement of the edge states. The appearance of Dirac cones and the formation of PFTI is strongly affected by the nonlinear susceptibilities; i.e. the PFTI can be shut off by the third-order nonlinear susceptibility and re-opened up by the fifth-order one.