“Representation Theory for Massless Quasiparticles in BdG Systems” by Prof Zheng-Xin LIU on Tuesday, July 2, 2024, 4:00 pm CYMP 522, HKU
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.
“Topological photonics and non-Hermitian optics with the synthetic frequency dimension” by Prof Luqi YUAN on Monday, May 20, 2024, 11:00 am CYMP 522, HKU
Over the past few years, synthetic dimensions in photonics have been rapidly developing
and generating significant interest. By utilizing different degrees of freedom of light,
synthetic dimensions can be constructed. This seminar will focus on the creation of a
synthetic frequency dimension in dynamically modulated ring resonator systems.
“High Energy Physics Opportunities in the Quantum Computing Era” by Prof Ying Ying LI on Thursday, May 16, 2024, 4:00 pm CYMP 522, HKU
Quantum simulation of High Energy Physics (HEP) has seen remarkable growth in
recent years. Nevertheless, there is a continuous need for advancements in the overall
simulation framework. In my talk, I will first motivate the critical need for quantum
computing in HEP and discuss recent developments.
“A morphism between two QFTs” by Prof Liang KONG on Friday, May 31, 2024, 3:00 pm MW103, HKU
Over the past few years, synthetic dimensions in photonics have been rapidly developing
and generating significant interest. By utilizing different degrees of freedom of light,
synthetic dimensions can be constructed. This seminar will focus on the creation of a
synthetic frequency dimension in dynamically modulated ring resonator systems.
HKIQST Distinguished Visitor Series by Prof. Xian-Min JIN “The Era of Photonic Chip” on Tuesday, 23 April 2024, 10:30 a.m. CYMP 525, HKU
As the era of quantum computing and artificial intelligence
gradually approaches, the demand for photon chips is rapidly increasing,
making it the next fiercely contested high ground. No country in the world has
yet built a complete photonic integration ecosystem, which provides a
significant opportunity for China to take the lead in the post-Moore era.
Introduction to Superconductivity
This series of lectures are intended for interested undergraduate and graduate students. They
cover the fundamental aspects of classic superconductors and their explanations in terms of
the BCS theory of superconductivity.
