Honoring the Legacy of Professor Sir Anthony James Leggett, Nobel Laureate in Physics

Prof. Sir Anthony James Leggett, Nobel Laureate and Advisory Committee Chair, Passes Away at 87

It is with deep sorrow that we announce the passing of Professor Sir Anthony James Leggett on March 8, 2026, at the age of 87. As the chair of the advisory committee of the Hong Kong Institute of Quantum Science & Technology (HKIQST) and a distinguished 2003 Nobel Laureate in Physics, his contributions have left an indelible mark on the scientific community.

Beyond his work on superfluid Helium-3, for which he was awarded the 2003 Nobel Prize, he pioneered the study of the quantum mechanics of collective variables, and, importantly, the phenomena of quantum coherence and tunnelling in the presence of a dissipative environment. This led not only to a substantial body of technical work, but also to a deeper understanding of quantum mechanics as applied to macroscopic systems.

Since 2014, he has served as an advisor to the Center of Theoretical and Computational Physics at the University of Hong Kong. Most recently, as chair of the advisory committee for HKIQST, he provided invaluable advice, contributed to the selection of Dan Tsui Fellows, and delivered a series of ten lectures on superconductivity in 2024.

We extend our heartfelt condolences to his family and friends. Professor Leggett’s legacy will continue to inspire future generations of scientists. He will be dearly missed.

APS Global Physics Summit 2026 Hong Kong Meeting Announced – HKIQST joins APS and PSHK as co-hosts| Monday, 23-27 March 2026 | HKPC Building, HK

HKIQST Co-Hosts APS Global Physics Summit 2026 Hong Kong Meeting – Strengthening Hong Kong’s role as a hub for international physics collaboration. Early Abstract Deadline Announced – Oral abstracts submitted by 5 January 2026 may be selected for the APS Virtual Session, offering global visibility for regional researchers. On-Site Programme Highlights – The Hong Kong meeting (23–27 March 2026) will […]

“Algebraic Bethe Ansatz, Yang-Baxter Equation and All That” by Prof. Yunfeng JIANG | Tuesday, 24 – 26 February, 2026, HOC117/CYM522, HKU

This lecture series provides a systematic introduction to the Algebraic Bethe Ansatz (ABA), also known as the Quantum Inverse Scattering Method (QISM): a powerful framework for solving quantum integrable models exactly. We will begin with its basic construction, demonstrating how to obtain the exact spectra of paradigmatic models such as the Heisenberg spin chain, the Lieb-Liniger model, and the 6-vertex model. We will then explore the rich mathematical structure underlying the method, focusing on the central role of the Yang-Baxter equation and its profound connection to quantum group theory. If time permits, we will discuss extensions of the formalism to compute dynamical quantities, such as form factors and correlation functions, illustrating the full power of ABA as a tool for non-perturbative analysis in quantum theory.

CTCP Seminar: “Recognizing gapless phases in quantum many-body physics” by Prof. Yuan YAO | Wednesday, February 11, 2026, 4:00pm CYM522, HKU

The spectral gap of quantum many-body Hamiltonians is an important but difficult concept in condensed matter. Its identification is complicated and, quite often, controversial because the gap, together with the ground-state degeneracy is a thermdynamic limit notion rather than any finite-size energy splitting.

In this talk, we will discuss a gaplessness indicator. Specifically, we prove that the ground state(s) of an SO(3)-symmetric gapped spin chain must be spin singlet(s), and the expectation value of a twisting operator asymptotically approaches unity in the thermodynamic limit, where finite-size corrections are inversely proportional to the system size. This theorem provides (i) supporting evidence for various conjectured gapped phases, and, contrapositively, (ii) a sufficient criterion for identifying gapless spin chains. We test the efficiency of our theorem by numerical simulations for a variety of spin models and show that it indeed offers a novel efficient way to identify gapless phases in spin chains with spin-rotation symmetry.

CTCP Seminar: “Mesoscopic Non-Hermitian Physics and Theory of Non-Hermitian Symmetry Breaking” by Prof. Wei CHEN | Tuesday, February 3, 2026, 4:00pm CYM522, HKU

In condensed matter physics, various physical phenomena can be effectively described using Green’s functions, typically corresponding to non-Hermitian Hamiltonians. Recent advancements in non-Hermitian physics have offered a fresh perspective to condensed matter physics, leading to exploration of non-Hermitian self-energies with intricate structures. One intriguing non-Hermitian phenomenon is the non-Hermitian skin effect, characterized by the nonreciprocal propagation of wave packets within the system and the accumulation of bulk states at open boundaries. In this talk, I will discuss the implementation and control of the non-Hermitian skin effect in mesoscopic electronic systems. Specifically, the conventional, spin-, and valley-resolved non-Hermitian skin effect can be realized through complex band engineering in mesoscopic heterostructures, resulting in nonreciprocal electron transport phenomena. This effect holds promise for the development of robust electronic devices, such as valley filters. Additionally, the application of a magnetic field can suppress the skin effect, providing an effective means for its control. In the second part of the talk, we will introduce a general framework for non-Hermitian spontaneous symmetry breaking. The transition of energy spectra from real to complex values, together with the accompanying spontaneous symmetry breaking of eigenstates, is one of the central topics in non-Hermitian physics. However, a complete and universal theory that characterizes the properties of individual energy levels has been lacking. By employing the complex path integral formalism and developing a generalized Gutzwiller trace formula, we establish a universal quantum-classical correspondence that precisely connects the properties of single energy levels to the symmetries of their corresponding semiclassical orbits. This physical mechanism applies broadly to systems with pseudo-Hermitian symmetries and provides practical insights for the precise control of non-Hermitian phenomena.

“Towards Semiconductor Topological Photonics” by Prof. Xiao HU | Monday, January 12, 2026, 2:00pm CYM522, HKU

Transforming the concept of band topology fostered in electron systems to electromagnetic waves opens a completely new direction for harnessing propagation of light. It is observed that electromagnetic modes in honeycomb photonic crystals exhibit Dirac-type frequency dispersions, which are accompanied by emergent spin degree of freedom, and that deforming the honeycomb structure in a designed way gives birth to a photonic analogue of quantum spin Hall effect. In this talk I will first show that the main physics can be captured phenomenologically by the k∙p theory, and discuss that the photonic topology can be characterized in terms of the Wilson loops based on the C_2 T symmetry. Then I will introduce examples to demonstrate how the recipe can be exploited for harnessing light and deriving advanced optic properties.

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