HKIQST held its inaugural retreat on September 28, 2024

HK Institute of Quantum Science and Technology held its inaugural retreat on September 28, 2024, in Shenzhen. Following the signing of the Memorandum of Understanding (MOU), the delegation team engaged in discussions with the Quantum Science Center of the Guangdong-Hong Kong-Macao Greater Bay Area regarding potential future collaborations. Subsequently, the Institute conducted its first staff meeting chaired by Prof. Zidan Wang. During the retreat,  the team members visited two laboratories: Phase 1.5  Sun-Laboratory and  Phase2 Zhongtian-YuanLaboratory. To foster team spirit, we concluded the day with a team-building dinner.

CTCP Seminar : “Noninvertible Gauge Symmetry in (2+1)d Topological Orders: A String-Net Model Realization” by Prof. Yidun WAN on Friday, Sept 20, 2024, 4:00 pm | CYMP 522

We develop a systematic framework for understanding symmetries in topological phases in 2+1 dimensions using the string-net model, encompassing both gauge symmetries that preserve anyon species and global symmetries permuting anyon species, including both invertible symmetries describable by groups and noninvertible symmetries described by categories. As an archetypal example, we reveal the first noninvertible categorical gauge symmetry of topological orders in 2+1 dimensions: the Fibonacci gauge symmetry of the doubled Fibonacci topological order, described by the Fibonacci fusion 2-category. Our approach involves two steps: first, establishing duality between different string-net models with Morita equivalent input fusion categories that describe the same topological order; and second, constructing symmetry transformations within the same string-net model when the dual models have isomorphic input fusion categories, achieved by composing duality maps with isomorphisms of degrees of freedom between the dual models. If time permits, I will also talk about a subsequent work on anyon condensation.

Young Scientist Yi Yang Wins Prestigious Croucher Innovation Award

HKIQST member, Prof. Yi Yang 楊易, has been awarded the prestigious Croucher Innovation Award (2024) for his groundbreaking research on nonrelativistic free-electron-light interaction with nanophotonics. Prof. Yang and his research team aim to realize strong free-electron-light interaction by interfacing slow nonrelativistic electrons with judiciously designed photonic environments, which has the potential to revolutionize electron microscopy and spectroscopy, and generate entangled electrons and photons for quantum light generation and manipulation. The synergy between free electron optics and nanophotonics has already led to new discoveries and applications, such as the stimulated inverse Cherenkov effect, entanglement between free electrons and photons, tunable integrated radiation sources and particle accelerators, and even biomedical imaging. Prof. Yang’s innovative approach to investigating the interplay between nonrelativistic electrons, Van der Waals materials, and nanostructures has the potential to explore quantum recoil, spin polarization, and multi-photon emission processes.

“Representation Theory for Massless Quasiparticles in BdG Systems” by Prof Zheng-Xin LIU on Tuesday, July 2, 2024, 4:00 pm | CYMP 522

Linearly dispersive gapless quasiparticles can appear at general momentum points of superconductors due to topological reasons like K theory or symmetry indicators theory. However, the zero modes associated with these quasiparticles are generally ‘accidental’ from symmetry point of view. In this talk, we apply projective representation (rep) theory to analyze the bulk gapless quasiparticles in BdG systems. Different from the description of semimetals, we need to specially treat the particle-hole ‘symmetry’ since it is anti-comm-uting with the BdG Hamiltonian. Hence the notion of ‘simple irreducible reps (irreps)’ and ‘composite irreps’ are introduced to label the energy modes. We show that without charge conjugation symmetry (unitary symmetry that commutes with the Hamiltonian), no robust bulk zero modes exist at any fixed momentum point in the bulk. However, robust zero modes at certain high symmetry momentum points can be protected by (effective) charge conjugation symmetries, resulting in gapless quasiparticles with linear, quadratic, or higher-order dispersions determined by the effective k · p theory. The low energy physical properties of the system are determined by the rep carried by the zero modes. This theory provides a framework to classify nodal Superconductors/Superfluids/Quantum Spin Liquids with specified (projective) symmetry group and sheds light on the realization of Majorana-type massless quasiparticles in condensed matter physics.

“A morphism between two QFTs” by Prof Liang KONG on Friday, May 31, 2024, 3:00 pm | MW103

A morphism between two mathematical objects of the same type (e.g. groups, algebras, representations, categories, etc.), which preserves the defining structures of the objects, is one of the most important notions in mathematics. However, how to define such a morphism between two QFT’s (or quantum phases) had never been considered in physics until arXiv:1502.01690. In this talk, I will give a review of this notion and discuss its applications in the study of topological orders and more general quantum liquids. I will also clarify its relation with “topological symmetry” or “SymTFT”.

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