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 Electric Fields and Spin-Orbit Coupling in Photonic Synthetic Dimensions
In this work, we theoretically synthesize spin-orbit coupling (SOC) and non-Abelian electric field in a polarization-maintaining fibre ring resonator in the synthetic dimension. By introducing pseudo spin-dependent modulation in the ring resonator, this gives rise to SU(2) non-Abelian gauge field in the synthetic dimension. We perform signal extraction and projection detection of SOC that is expected to be realizable in the experiment. We perform both electromagnetic simulation and analytical quantum mechanics calculation to study the dynamics exhibited by non-Abelian electric fields, demonstrating Zitterbewegung in addition to Bloch oscillation that is contributed by normal Abelian electric fields.
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.
