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Fall 2022 Physics Colloquium


Schedule:From September 7 to November 30, 2022 (Every other Wednesday)
September 7, 2022 (Wed) 5:00 p.m.
September 21, 2022 (Wed) 5:00 p.m.
October 5, 2022 (Wed) 5:00 p.m.
October 19, 2022 (Wed) 5:00 p.m.
November 2, 2022 (Wed) 5:00 p.m.
November 16, 2022 (Wed) 10:00 a.m.
November 30, 2022 (Wed) 5:00 p.m.

PhysicsColloquium

From the fall semester of 2021, the colloquium will happen on every other Wednesday either at 10-11am or 5-6pm. The detailed schedule and talk information are as below.
For inquiries or suggestions of future speakers, please contact the colloquium working group (Dr. Jane Lixin Dai, Dr. Tran Trung Luu, Dr. Yanjun Tu, Dr. Chenjie Wang, and Dr. Shizhong Zhang).


Astrophysical Black Holes
(Joint Colloquium of the Department of Physics and the HKU-UCAS Joint Institute of Theoretical and Computational Physics)

Speaker: Prof. Cosimo BAMBI
Affiliation: Fudan University
Date: September 7, 2022 (Wednesday)
Time: 5:00 p.m.
Zoom Link: https://bit.ly/3KgAxhu
Meeting ID: 970 4476 0018
Password: 2859
Poster: Download
Abstract:
In this talk, I will review the development of the field, from the first speculations to the current lines of research. According to Einstein's theory of general relativity, black holes are relatively simple objects and completely characterized by their mass, spin angular momentum, and electric charge, but the latter can be ignored in the case of astrophysical macroscopic objects. Search for black holes in the sky started in the early 1970s with the dynamical measurement of the mass of the compact object in Cygnus X-1. In the past 10-15 years, astronomers have developed some techniques for measuring the black hole spins. Recently, we have started using astrophysical black holes for testing fundamental physics.
Key References:
https://ui.adsabs.harvard.edu/abs/2018AnP...53000430B/abstract
https://ui.adsabs.harvard.edu/abs/2020mbhe.confE..28B/abstract

Active and passive non-Hermitian devices

Speaker: Prof. Henning SCHOMERUS
Affiliation: Lancaster University
Date: September 21, 2022 (Wednesday)
Time: 5:00 p.m.
Zoom Link: https://bit.ly/3KyAWfv
Meeting ID: 921 1310 5357
Password: 2859
Poster: Download
Abstract:
In photonic systems, gain and loss can be used to induce intriguing effects that are linked to non-Hermitian and topological physics. Prominent examples are exceptional points and the non-Hermitian skin effect, which can be used for enhanced sensing and directed amplification, as well as symmetry-protected states, which can be addressed by topological mode selection. Many of these applications make explicit use of mode nonorthogonality, which becomes especially intriguing when the system is nonreciprocal. I describe how these effects can be probed in response theory, transport, and scattering, and highlight fundamental practical limits of the observability of some effects.
Key References:
H Schomerus Phys. Rev. Lett. 104, 233601 (2010); Opt. Lett. 38, 1912-1914 (2013)
Phys. Rev. Research 2, 013058 (2020); arXiv:2207.09014 (2022)
Poli et al, Nat. Commun. 6, 6710 (2015); H Zhao et al Nat. Commun. 9, 981 (2018)

Twinkle twinkle little stars, how I wonder how you die

Speaker: Prof. Ming Chung CHU
Affiliation: Department of Physics, The Chinese University of Hong Kong
Date: October 5, 2022 (Wednesday)
Time: 5:00 p.m.
Venue: MWT5, 1F, Meng Wah Complex, The University of Hong Kong
Poster: Download
Abstract:
Supernovae – explosions of dying stars – are remarkable events that play an essential role in stellar evolution, as well as the spreading of elements and reshaping of the matter distribution in the universe. The study of supernovae is entering a golden age with many new observational tools utilizing neutrino, gravitational-wave, and electromagnetic-wave observations, and exciting discoveries are expected. I will introduce three types of supernovae: Thermonuclear, Accretion-induced collapse, and Core-collapse supernovae, and how they might be used to detect dark matter and quark deconfinement.
Key References:
1. Delayed Detonation Thermonuclear Supernovae with an Extended Dark Matter Component, H. S. Chan, M.-C. Chu, S.C. Leung, and L.M. Lin, The Astrophysical Journal 914,138 (2021)
2. Gravitational-wave Signature of a First-order Quantum Chromodynamics Phase Transition in Core-Collapse Supernovae, S. Zha, E. O’Connor, M.–C. Chu, L.M. Lin, S. Couch, Physical Review Letters 125, 051102 (2020)
3. Accretion-Induced Collapse of Dark Matter Admixed White Dwarfs -- II: Rotation and Gravitational-wave Signals, Shuai Zha, Ming-Chung Chu, Shing-Chi Leung, Lap-Ming Lin, The Astrophysical Journal 883, 13 (2019)

Thermodynamics and order beyond equilibrium – from eigentstate thermalisation to time crystals

Speaker: Prof. Roderich MOESSNER
Affiliation: Max Planck Institute for the Physics of Complex Systems in Dresden, Germany
Date: October 19, 2022 (Wednesday)
Time: 5:00 p.m.
Zoom Link: https://bit.ly/3DSdNmV 
Meeting ID: 967 7300 3194 
Password: 2859
Poster: TBC
Abstract:
The field of thermodynamics is one of the crown jewels of classical physics. Thanks to the advent of experiments in cold atomic systems with long coherence times, our understanding of the connection of thermodynamics to quantum statistical mechanics has seen remarkable progress.
Extending these ideas and concepts to the non-equilibrium setting is a challenging topic, in itself of perennial interest. Here, we present perhaps the simplest non-equilibrium class of quantum problems, namely Floquet systems, i.e. systems whose Hamiltonians depend on time periodically, H(t + T) = H(t). For these, there is no energy conservation, and hence not even a natural concept of temperature.
We find that certain structures from equilibrium thermodynamics are lost, while entirely new non-equilibrium phenomena can arise, including a spectacular spatiotemporal `time-crystalline' form of order, recently observed experimentally on google AI's sycamore NISQ platform.
Key References:
For an introductory overview, see Nature Physics 13, 424–428 (2017)
For an in-depth review, see arxiv:1910.10745 . NISQ experiment: Nature 601, 531 (2022).

TBC

Speaker: Prof. Bei ZENG
Affiliation: The Hong Kong University of Science and Technology
Date: November 2, 2022 (Wednesday)
Time: 5:00 p.m.
Venue: MWT5, 1F, Meng Wah Complex, The University of Hong Kong
Poster: TBC
Abstract: TBC
Key References:
TBC

TBC

Speaker: Prof. Roger ROMANI
Affiliation: Stanford University
Date: November 16, 2022 (Wednesday)
Time: 10:00 a.m.
Zoom Link: TBC
Meeting ID: TBC
Password: TBC
Poster: TBC
Abstract: TBC
Key References:
TBC

TBC

Speaker: Prof. Stephanie WEHNER
Affiliation: TBC
Date: November 30, 2022 (Wednesday)
Time: 5:00 p.m.
Zoom Link: TBC
Meeting ID: TBC
Password: TBC
Poster: TBC
Abstract: TBC
Key References:
TBC