“High-Tc superconductivity based on low-dimensional materials platforms” by Prof. Zhenyu ZHANG on Thursday, November 6, 2025, 4:30pm Room 522, 5/F, Chong Yuet Ming Physics Building, HKU
Discoveries of new superconductors with high transition temperatures have been a perpetual drive of condensed matter physics. In this talk, I attempt to give an overview on recent advances in this vibrant area, with some of own stories squeezed in. We start from predictive designs of freestanding or supported superconducting monolayers that may exhibit high-Tc superconductivity, as well as low-dimensional systems that display exotic Ising, chiral, or p-wave superconductivity. On the mechanistic side, I will demonstrate how plasmonic excitations or pronounced correlation effects can enhance the superconductivity of iron-based superconductors, and predict designer substrates that may optimize the strain in La3Ni2O7 thin films for maximally enhanced Tc.
“Epitaxial Large-gap topological insulator on semiconductor for seamless device integration” by Prof. Feng LIU on Thursday, November 6, 2025, 3:30pm Room 522, 5/F, Chong Yuet Ming Physics Building, HKU
Significant advances have been made in fundamental research of topological insulators (TIs), yet their device applications remain elusive. We propose an approach towards seamless integration of two-dimensional (2D) TIs into semiconductor devices. Using first-principles calculations, we show that heteroepitaxially grown III-V semiconductor ultrathin films can self-convert into 2D TIs. Remarkably, on GaSb(111) monolayer GaAs1-xBix becomes universally a 2D TI at any alloy concentration, x, enabled by natural formation of semiconductor heterojunctions. For the GaAs-rich monolayer, having type-II (III) band alignment with GaSb, an intriguing interfacial band offset inversion emerges between surface Ga-s and substrate Sb-p bands; for the GaBi-rich monolayer, with type-I (I’) alignment, the conventional intra-surface band gap inversion arises between Ga-s and Bi-p bands. The lattice-matching epitaxy of GaAs0.25Bi0.75 alloy enables growth of thin-film 2D TIs with a gap up to ~330 meV. Our findings pave the way to engineering wafer-scale large-gap 2D TIs to potentially operate at room temperature.
HK Forum on Quantumology 香港量子學論壇| Sunday, 23 November 2025 | RHT HKU
We are pleased to announce the HK Forum on Quantumology香港量子學論壇 , held in celebration of the International Year of Quantum Science and Technology (IYQ). The event is organized by the HK Institute of Quantum Science and Technology in collaboration with the HK Branch of the Quantum Science Centre of the Guangdong-Hong Kong-Macau Greater Bay Area.
Scheduled for 23 November 2025 at the Rysan Huang Theatre, of HKU, this event offers a distinguished platform for academic exchange, collaboration, and innovation in quantum science and technology.
You are cordially invited to participate in a series of engaging activities, including keynote and invited talks, as well as roundtable discussions featuring leading quantum scientists.
Physics Colloquium: “Cold-atom quantum sensing via Bayesian quantum estimation” by Prof. Chaohong LEE on Wednesday, October 22, 2025, 10:30 am MWT2, G/F, Meng Wah Complex, HKU
Quantum sensors based on frequentist interferometry face a trade off between
sensitivity and dynamic range Bayesian quantum estimation, combining Bayesian
statistics with quantum metrology, can surpass the limit of conventional frequentist measurements For cold atom CPT clocks, our adaptive Bayesian protocol achieves
Heisenberg limited sensitivity in integration time and improves fractional frequency
stability by 5 1 4 dB over conventional PID locking while enhancing robustness against
technical noise In CPT magnetometry, we optimize measurement sequences to
improve precision scaling from T 0 5 to T 0 85 Using Bayesian quantum estimation to
optimize the interferometry sequence, we yield a 145 6 nT dynamic range 14 6 dB
higher than frequentist counterpart of 5 0 nT) with a sensitivity of 6 8 0 1 pT/Hz¹ ² 3 3
dB improvement over the frequentist counterpart of 14 7 0 4 pT/Hz¹ ²) In addition to atomic clocks and magnetometers, this framework may bridge high sensitivity and broad dynamic range for other interferometry based quantum sensors.
CTCP Seminar “A 2D-CFT Factory: Critical Lattice Models from Competing Anyon Condensation in SymTO” by Prof. Yidun WAN | September 25, 2025, 4:30pm Room 522, 5/F, Chong Yuet Ming Physics Building
In this talk, we shall introduce a CFT factory – a novel algorithm of methodically generating 2D lattice models that would flow to conformal field theories (CFTs) in the infrared. We realise these models by engineering the boundary conditions of 3D topological orders (SymTOs) described by string-net models. The critical points are induced by a commensurate condensation of non-commuting anyons. Our structured method generates an infinite family of critical lattice models, including the A-series minimal models, and uncovers previously unknown critical points. Notably, we discover at least three novel CFTs (with central charge c around 1.3, 1.8, and 2.5) that preserves the Haagerup symmetries, in addition to recovering previously reported examples. The non-invertible symmetries preserved at these points are dictated by a novel “refined condensation tree”. The condensation trees predict large swathes of phase boundaries and sieves out second order phase transitions. This predictive power is illustrated not only in well-studied examples, such as the 8-vertex model associated with the A5 category, but also in new cases involving Haagerup symmetries, validated by an improved symmetry-preserving tensor-network renormalization group method. The critical couplings are precisely encoded in algebraic data (the Frobenius algebras and quantum dimensions of unitary fusion categories), thereby establishing a powerful and systematic route to the discovery and potential classification of new CFTs.
Joint Seminar: “Beyond Closed Wave Systems: Non-Hermiticity, Nonlinearity, and Casimir Effect” by Prof. Kun DING | Wednesday, August 20, 2025, 11:00am CYMP522
The classical wave system has demonstrated itself as an excellent platform to realize and
investigate novel phenomena and physics. The bedrock principle is to utilize the macroscopic
quantities obtained from the homogenization or mean-field treatment. However, it usually deals
with Hermitian problems and averages out fluctuations. Therefore, the presentation will cover two
topics: non-Hermitian physics and Casimir effect. The first part focuses on the impact of non
Hermitian ingredients on soliton formation and dynamics. By constructing a soliton phase diagram,
two distinct soliton phases and their transitions are identified. A Wannier-function-based nonlinear
Hamiltonian shows that soliton formation critically depends on how skin-mode localization and
band nonreciprocity suppress or enhance wave dispersion. Both soliton phases have been
demonstrated to be dynamically accessible from bulk and edge excitations. The second part
discusses the influence of the metal’s surface electrons on Casimir forces. A three-dimensional
frame transformation method has been established by embedding mesoscopic boundary conditions
of electromagnetic fields. We find that mesoscopic Casimir forces are sensitive to the surface
electron behavior, including spill-in and spill-out, as verified by the multiple scattering method and
proximity force approximation. The mechanism has finally been revealed as Casimir softening
distances rooted in quantum surface responses of electrons.
CTCP Seminar: “Testing Multipartite Nonlocality and Network Nonlocality Sharing” by Prof. Qing CHEN | Tuesday, June 17, 2025, 10:00am CYMP522
After a brief introduction to quantum nonlocality, we propose a set of conditions on the joint probabilities as a test of genuine multipartite nonlocality, and it turns out that all entangled symmetric multipartite qubit states pass this test. In the following we generalize this test to a family of Hardy-type tests, which can detect different degrees of nonlocality ranging from standard to genuine multipartite nonlocality. At last, we explore network nonlocality sharing in an n-branch generalized star network scenario with m observers in each branch and k settings per observer.
CTCP Seminar: “Authentication of Classical Channels in Quantum Key Distribution” by Prof. Liujun WANG | Monday, June 16, 2025, 3:00pm CYMP522
Quantum Key Distribution (QKD) offers information-theoretic security but relies critically on authenticated classical channels for post-processing steps (e.g., basis sifting and key reconciliation). Without authentication, these channels are vulnerable to man-in-the-middle attacks. Traditional methods require Alice and Bob to pre-share symmetric keys via physical meetings—a solution incompatible with multi-user QKD networks. We experimentally demonstrate a practical solution using post-quantum signature algorithms to authenticate QKD classical channels. This approach was validated under multiple QKD network topologies in laboratory environments and a real-world metropolitan QKD network operating continuously for 36 days. Our implementation provides quantum-resistant security while uniquely requiring only short-term security (e.g., ~1 second during authentication), contrasting with long-term security assumptions for post-quantum encryption. Additionally, we propose a quantum-teleportation-based protocol for message authentication that simultaneously ensures confidentiality—enabling secure key reconciliation in QKD.
CTCP Seminar: “Origin of Topological Holography” by Prof. Tian LAN | Friday, June 6, 2025, 4:30pm CYMP522
There is a holographic correspondence between (1) nD quantum systems with symmetry C and (2) nD boundaries of the n+1D topological order Z(C), where Z(C) is mathematically the Drinfeld center of C. Such mysterious topological holography has numerous applications and consequences, especially in the recent emerging field of generalized symmetry. By a rigorous construction and proof in 1+1D, we show that the Drinfeld center Z(C) naturally arise as the category of fixed-point local tensors with symmetry C, thus revealing the origin of topological holography. This talk is based on arXiv:2412.07198.
CTCP Seminar: “Deep Boundary Perturbations at a Quantum Critical Point” by Dr. Shang LIU | Wednesday, March 19, 2025, 3:30pm KKLG101
We explore an unconventional class of problems in the study of (quantum) critical
phenomena, termed “deep boundary criticality”. Traditionally, critical systems are analyzed with two types of perturbations: those uniformly distributed throughout the bulk, which can significantly alter the bulk criticality by triggering a nontrivial bulk renormalization group
flow, and those confined to a boundary or subdimensional defect, which affect only the boundary or defect condition. Here, we go beyond this paradigm by studying quantum critical systems with boundary perturbations that decay algebraically (following a power law) into the bulk. By continuously varying the decay exponent, such perturbations can
transition between having no effect on the bulk and strongly influencing bulk behavior. We investigate this regime using two prototypical models based on (1+1)D massless Dirac fermions. Through a combination of analytical and numerical approaches, we uncover exotic scaling laws in simple observables and observe qualitative changes in model behavior
as the decay exponent varies.
