Fermionic time-reversal symmetry in a photonic topological insulator

Abstract

Much of the recent enthusiasm directed towards topological insulators as a new state of matter is motivated by their hallmark feature of protected chiral edge states. In fermionic systems, Kramers degeneracy gives rise to these entities in the presence of time-reversal symmetry (TRS). In contrast, bosonic systems obeying TRS are generally assumed to be fundamentally precluded from supporting edge states. In this work, we dispel this perception and experimentally demonstrate counter-propagating chiral states at the edge of a time-reversal-symmetric photonic waveguide structure. The pivotal step in our approach is encoding the effective spin of the propagating states as a degree of freedom of the underlying waveguide lattice, such that our photonic topological insulator is characterised by a ${\mathbb{Z}}_2$-type invariant. Our findings allow for fermionic properties to be harnessed in bosonic systems, thereby opening new avenues for topological physics in photonics as well as acoustics, mechanics and even matter waves.

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• Floquet higher order topological insulator in a periodically driven bipartite lattice
• On-chip beam rotators, adiabatic mode converters, and waveplates through low-loss waveguides with variable cross-sections
• Photonic ${\mathbb{Z}}_2$ topological Anderson insulators
• Topological origin of quantized transport in non-Hermitian Floquet chains
• Spin-Polarized Fractional Corner Charges and Their Photonic Realization
• Dynamical Detection of Topological Spectral Density
• Non-Floquet engineering in periodically driven non-Hermitian systems
• Four-dimensional Floquet topological insulator with an emergent second Chern number
• Cutting off the non-Hermitian boundary from an anomalous Floquet topological insulator
• Five-dimensional Floquet topological semimetals with emergent Yang monopoles and linked Weyl surfaces
• Controlling the direction of topological transport in a non-Hermitian time-reversal symmetric Floquet ladder
• Quantized charge transport in disordered Floquet topological insulators in the absence of Anderson localization
• Interaction-Induced Higher-Order Topological Insulator via Floquet Engineering
• Quantitative measure of topological protection in Floquet systems through the spectral localizer
• Real and imaginary edge states in stacked Floquet honeycomb lattices
• Immutable quantized transport in Floquet chains