YANG GROUP @ HKU PHYSICS
Photonic synthetic gauge fields
Synthetic gauge fields enable the versatile creation and manipulation of topological phenomena in photonic systems.
Some selected representative works are as follows.
Synthetic non-Abelian gauge fields for non-Hermitian systems

Non-Abelian gauge fields have primarily been explored in Hermitian systems, where gauge flux is traditionally defined along closed loops.
By introducing a generalized Hatano-Nelson model with imbalanced non-Abelian hopping, we reveal that non-Abelian gauge fields can manifest rich non-Hermitian topological effects, even without gauge flux in one dimension.
Our investigation uncovers the emergence of non-Hermitian skin modes at the ends of open chains under non-Abelian gauge fields, with populations effectively tuned near exceptional points. Extending our analysis to two dimensions, we observe the breakdown of gauge invariance of Wilson loops in non-Hermitian lattices addressed with non-Abelian gauge fields.
HOTI from momentum-space nonsymmorphic symmetry
Based on a checkerboard-pattern Z2 synthetic gauge field, we reported a pair of anti-commutative momentum-space glide reflections and the resulting higher-order topological phenomena. This system is featured by a phase diagram where boundary obstruction can appear within a symmetric-protected bulk.


Non-Abelian physics in light and sound
This work provides a comprehensive and coherent review of non-Abelian physics in light and sound, an emergent topic fundamentally important for the understanding of bosonic systems with potential applications in information multiplexing in optoelectronics and acoustics.
Synthesis of non-Abelian gauge fields in real space
Synthesizing non-Abelian gauge fields has been challenging because of its requirement of matrix-valued potentials. In this work, we report an experimental synthesis of non-Abelian gauge fields in real space and the observation of the non-Abelian Aharonov-Bohm
effect. Using optical mode degeneracy, we employed temporal modulation and the Faraday effect
to break time-reversal symmetry in orthogonal bases of the Hilbert space and synthesize tunable
non-Abelian gauge fields. The non-commutativity of the gauge fields is demonstrated by the Sagnac
interference of two final states obtained by reversely ordered path integrals.
