Measuring non-Abelian quantum geometry and topology in a multi-gap photonic lattice

TL;DR

This paper reports the first direct measurement of non-Abelian quantum geometric tensor in a multi-gap photonic lattice, revealing non-Abelian topological properties and quaternion charges.

Contribution

It introduces a novel orbital-resolved polarimetry technique to experimentally access non-Abelian quantum geometry in a six-band 2D synthetic lattice.

Findings

Successfully measured non-Abelian quaternion charges and Euler curvature.

Demonstrated direct access to non-Abelian quantum metric for all bands.

Enabled exploration of non-Abelian topological phases in photonic systems.

Abstract

Recent discoveries in semi-metallic multi-gap systems featuring band singularities have galvanized enormous interest in particular due to the emergence of non-Abelian braiding properties of band nodes. This previously uncharted set of topological phases necessitates novel approaches to probe them in laboratories, a pursuit that intricately relates to evaluating non-Abelian generalizations of the Abelian quantum geometric tensor (QGT) that characterizes geometric responses. Here, we pioneer the direct measurement of the non-Abelian QGT. We achieve this by implementing a novel orbital-resolved polarimetry technique to probe the full Bloch Hamiltonian of a six-band two-dimensional (2D) synthetic lattice, which grants direct experimental access to non-Abelian quaternion charges, the Euler curvature, and the non-Abelian quantum metric associated with all bands. Quantum geometry has been highlighted to play a key role on macroscopic phenomena ranging from superconductivity in flat-bands, to optical responses, transport, metrology, and quantum Hall physics. Therefore, our work unlocks the experimental probing of a wide phenomenology of multi-gap systems, at the confluence of topology, geometry and non-Abelian physics.