Past Events

back to listing

Spring 2022 Physics Colloquium


Date:From January 26 to April 20, 2022 (Every other Wednesday)
January 26, 2022 (Wed) 10:00 a.m.
February 9, 2022 (Wed) 10:00 a.m.
February 23, 2022 (Wed) 10:00 a.m.
March 9, 2022 (Wed) 10:00 a.m.
March 23, 2022 (Wed) 5:00 p.m. Canceled
March 30, 2022 (Wed) 10:00 a.m. (was February 23, 2022)
April 6, 2022 (Wed) 10:00 a.m. (was March 30, 2022)
April 20, 2022 (Wed) 10:00 a.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).

April 20, 2022 (Wed) 10:00 a.m.


Towards Precision Astrophysics for Warm Ionized Gas

Speaker: Prof. Renbin Yan
Affiliation: The Chinese University of Hong Kong
Date: January 26, 2022 (Wednesday)
Time: 10:00 a.m.
Zoom Link: https://hku.zoom.us/j/98211508095?pwd=Tm1KNGJ0YmpCdlBEY1ZMWjUvZ25kZz09
Meeting ID: 982 1150 8095
Password: 2859
Poster: Download
Abstract:
The interstellar medium is the fuel for star formation and AGN, and the sink for their feedback energy. It also records the history of star formation in its elemental abundances. The warm ionized gas is a major component of the ISM and has been extensively studied. However, there are still a number of mysteries about the ionization mechanisms for such gas in quiescent galaxies and quiescent regions of galaxies. Even for star-forming regions which are most well studied, there are still a large number of discrepant results in the literature about their metallicity, their elemental abundance pattern, and ionization states. I would present our efforts in solving these mysteries and resolving those discrepancies, and describe a roadmap towards an era in which we can model the astrophysics of warm ionized gas with precision, in the same style as Precision Cosmology. I will also introduce the design of a cost-effective, high spectral resolution, integral field spectrograph. When paired with a small telescope like a telephoto lens or arrays of them, it could provide unprecedented data to help us better understand star-forming HII regions and the feedback of star formation.

Quest for Strong Field Physics Research with a multi-PW Laser

Speaker: Prof. Chang Hee Nam
Affiliation: Gwangju Institute of Science and Technology, Korea
Date: February 9, 2022 (Wednesday)
Time: 10:00 a.m.
Zoom Link: https://hku.zoom.us/j/98801501062?pwd=RlV6S2JONUlzRjNOUVFnTDJOaGxjQT09
Meeting ID: 988 0150 1062
Password: 2859
Poster: Download
Abstract:
Ever since the Nobel Prize winning invention of the chirped pulse amplification technique in 1985, ultrashort high power lasers have been developed and applied to strong field physics research. At Center for Relativistic Laser Science (CoReLS), ultrahigh power lasers have been developed for the investigations of relativistic laser-matter interactions, laser-driven charged particle acceleration, laboratory astrophysics, and strong field quantum electrodynamics. CoReLS has upgraded its PW laser beamline to a 4PW laser in 2017 and achieved the record-breaking laser intensity of 10^23 W/cm2 in 2021. By applying the laser wakefield acceleration, we have produced multi-GeV electrons and used them for exploring nonlinear Compton scattering for the research of strong field quantum electrodynamics (QED) phenomena, predicted to occur in astrophysical objects, such as supernova, magnetar and black hole. In this presentation, after introducing the basic principle and optical structure of the CoReLS PW laser, the strong field research program at CoReLS will be explained.

Wave Dark Matter and Pulsar Arrays

Speaker: Prof. Tao Liu
Affiliation: The Hong Kong University of Science and Technology
Date: February 23, 2022 (Wednesday) March 30, 2022 (Wednesday) April 6, 2022 (Wednesday)
Time: 10:00 a.m.
Zoom Link: https://hku.zoom.us/j/94229961949?pwd=Sm82M2ZxOHY4cW5VZVcxN2tBcEhKdz09
Meeting ID: 942 2996 1949
Password: 2859
Poster: Download
Abstract:
Dark Matter (DM) is a long-standing puzzle on the Universe, while wave DM is one of the main theories to address this puzzle. In this talk, the speaker will introduce how pulsar arrays, which were originally proposed to detect low-frequency gravitational waves as a galactic interferometer, stands in the frontier of detecting wave DM. The speaker will specifically address in this context: (1) the role of individual pulsars; (2) the importance of developing ``pulsar polarization arrays''; and (3) the necessity of correlating pulsar polarization arrays and pulsar timing arrays. The detection of wave DM thus forms an important task for radio astronomy.

Interstellar Object: the ‘Oumuamua Conundrum

Speaker: Prof. Douglas Lin
Affiliation: University of California, Santa Cruz
Date: March 9, 2022 (Wednesday)
Time: 10:00 a.m.
Zoom Link: https://hku.zoom.us/j/95510656893?pwd=NFhmdDJEVWRveUhBTkJzVEt4d3hSZz09
Meeting ID: 955 1065 6893
Password: 2859
Poster: Download
Abstract:
In 2017, astronomers detected an elongated object swinging past Earth on its way out of the solar system. The size and motion of ‘Oumuamua (roughly “scout” in Hawaiian) inspired a few excited researchers to suggest the visitation of an interstellar “spaceship.” We revisited this scenario's three key assumptions: 1) spacecraft removes the large population requirement, 2) solar sail is responsible for the non gravitational acceleration, and 3) a tumbling oblate spheroid accounts for the light curve.  We show that such an object would 1) drift way off course during its passage through the turbulent, magnetized interstellar medium (similar to air dropping of pamphlets to intended targets on a gusty day), 2) endure comparable amount of radiation-driven acceleration in the anti-solar and sideway direction (contrary to their observed values), and 3) have extremely dim phases when the Sun crosses the surface plane of the thin hypothetical solar sail (analogous to Saturn's ring-plane crossing). Instead, we explore the physical nature of ‘Oumuamua and a vast fleet of its cohorts and show that they are likely to be the debris of tidally disrupted comets around common low-mass stars.

Towards a Quantum Internet

Speaker: Prof. Stephanie Wehner
Affiliation: QuTech, Delft University of Technology
Date: March 23, 2022 (Wednesday) 5:00 p.m. Canceled
Time: 5:00 p.m.
Zoom Link: https://hku.zoom.us/j/99525979547?pwd=YUxRMkhNZERlc3h1M3Juc3NhRUl2UT09
Meeting ID: 995 2597 9547
Password: 2859
Poster:Download
Abstract:
The vision of a Quantum Internet is to provide fundamentally new internet technology by ultimately enabling quantum communication between any two points on earth. Such a Quantum Internet would – in synergy with the ‘classical’ internet that we have today - connect quantum processors in order to achieve new capabilities that are provably impossible using classical communication. In this talk, we provide an introduction to quantum (internet-) working, and present recent results on the path of taking such a network from a physics experiment to a quantum network system. We report on the realization of the first quantum link layer protocol, now implemented on quantum hardware based on Nitrogen-Vacancy Centers in diamond. We conclude by presenting several tools that can be used to examine the experimental requirements of building larger quantum network, and be used by you to learn more about quantum networking beyond this talk.

Quantum Many-body theory in the Quantum Information era

Speaker: Prof. Matthew Fisher
Affiliation: University of California, Santa Barbara
Date: April 20, 2022 (Wednesday)
Time: 10:00 a.m.
Zoom Link: https://hku.zoom.us/j/91750678182?pwd=ODVySWFBZXB0RVhqbElJT1M5bFlBdz09
Meeting ID: 917 5067 8182
Password: 2859
Poster:Download
Abstract:
Traditionally, quantum many-body theory has focussed on ground states and equilibrium properties of spatially extended systems, such as electrons and spins in crystalline solids. In recent years “noisy intermediate scale quantum computers" (NISQ) have emerged, providing new opportunities for controllable non-equilibrium many-body systems. In such dynamical quantum systems the inexorable growth of non-local quantum entanglement is expected, but monitoring such open systems (by making projective measurements) can compete against entanglement growth. In this talk I will describe recent theoretical work exploring the behavior of “hybrid" quantum circuits consisting of both unitary gates and projective measurements. These circuits can be shown to exhibit a novel quantum dynamical phase transition between a weak measurement phase and a quantum Zeno phase. Detailed properties of the weak measurement phase - including relations to quantum error correcting codes - and of the critical properties of this novel quantum entanglement transition will be described.