Fall 2022 Schedule
Sep 13, 2022
Hsin Yuan Huang California Institute of Technology.
Host:
Pao-Ti Chang
Time: 2:20 pm
- 3:20 pm
Place: Room 104, CCMS-New Phys. building
Title:
Quantum advantage in learning from experiments
Abstract
Quantum technology has the potential to revolutionize how we acquire and process experimental data to learn about the physical world. An experimental setup that transduces data from a physical system to a stable quantum memory, and processes that data using a quantum computer, could have significant advantages over conventional experiments in which the physical system is measured and the outcomes are processed using a classical computer. We prove that, in various tasks, quantum machines can learn from exponentially fewer experiments than those required in conventional experiments. The exponential advantage holds in predicting properties of physical systems, performing quantum principal component analysis on noisy states, and learning approximate models of physical dynamics. In some tasks, the quantum processing needed to achieve the exponential advantage can be modest; for example, one can simultaneously learn about many noncommuting observables by processing only two copies of the system. Conducting experiments with up to 40 superconducting qubits and 1300 quantum gates, we demonstrate that a substantial quantum advantage can be realized using today's relatively noisy quantum processors. Our results highlight how quantum technology can enable powerful new strategies to learn about nature.
Brief Bio
Hsin-Yuan Huang (Robert) is a Ph.D. student at Caltech advised by John Preskill and Thomas Vidick. His research focuses on understanding how the theory of learning can provide new insights into physics, information, and quantum computing. Some of the central works include classical shadow tomography for learning large-scale quantum systems, provably efficient machine learning algorithms for solving quantum many-body problems, and the study of quantum advantages in machine learning. He has been awarded a Google PhD fellowship, the Quantum Creator Prize, MediaTek research young scholarship, and Kortschak scholarship.
Sep 20, 2022
Chung-Hou Chung National Yang Ming Chiao Tung University
Host:
Pao-Ti Chang
Time: 2:20 pm
- 3:20 pm
Place: Room 104, CCMS-New Phys. building
Title:
A mechanism for the strange metal phase in rare-earth intermetallic compounds
Abstract
A major mystery in strongly interacting quantum systems is the microscopic origin of the “strange metal” phenomenology, with unconventional metallic behavior that defies Landau’s Fermi liquid framework for ordinary metals. This state is found across a wide range of quantum materials, notably in rare-earth intermetallic compounds at finite temperatures (T) near a magnetic quantum phase transition, and shows a quasilinear-in-temperature resistivity and a logarithmic-in-temperature specific heat coefficient. Recently, an even more enigmatic behavior pointing toward a stable strange metal ground state (phase) was observed in CePd1−xNixAl, a geometrically frustrated Kondo lattice compound. Here, we propose a mechanism for such phenomena driven by the interplay of the gapless fermionic short-ranged antiferromagnetic spin correlations (spinons) and critical bosonic charge (holons) fluctuations near a Kondo breakdown quantum phase transition. Within a dynamical large-N approach to the Kondo–Heisenberg lattice model, the strange metal phase is realized in transport and thermodynamical quantities. It is manifested as a fluctuating Kondo-scattering–stabilized critical (gapless) fermionic spin-liquid metal. It shows ω/T scaling in dynamical electron scattering rate, a signature of quantum criticality. Our results offer a qualitative understanding of the CePd1−xNixAl compound and suggest a possibility of realizing the quantum critical strange metal phase in correlated electron systems in general.
Brief Bio
Chung-Hou Chung is a professor in the Department of Electrophysics, National Yang Ming Chiao Tung University, Taiwan. His research focuses on theoretical condensed matter physics with a special emphasis on quantum phase transitions, quantum critical phenomena and non-Fermi liquid behaviors in strongly correlated electron systems. His internationally impactful works include: quantum criticality in double quantum-dot system, non-equilibeium quantum phase transition in a dissipative resonant level, exotic spin liquid/superconducting states in undoped/doped frustrted quantum antiferromagnets, topological and Kondo insulators on honeycomb lattice.
Sep 27, 2022
Li-Chyong Chen Center for Condensed Matter Sciences, Center of Atomic Initiative for New Materials, Department of Physics, National Taiwan University
Host:
Pao-Ti Chang
Time: 2:20 pm
- 3:20 pm
Place: Room 104, CCMS-New Phys. building
Title:
Recent Trends in Artificial Leaves: Atomistic-design and Surface-probing Using Selective Two-dimensional Nanomaterials as Examples
Abstract
Photocatalytic CO2 conversion to hydrocarbon fuels, which makes possible simultaneous solar energy harvesting and CO2 reduction reaction (CO2RR), is considered a killing-two-birds-with-one-stone approach to solving the energy and environmental problems. However, the development of solar fuels has been hampered by the low photon-to-fuel conversion efficiency of the photocatalysts and lack of the product selectivity. Recent advances in development of integrated nanostructured materials have offered unprecedented opportunity for photocatalytic CO2RR. In 2D-layered nanomaterials (TMDCs and beyond), a perfect planar layer structure is usually inactive. Here, four cases with defect engineering (e.g. interstitial, vacancy, etc.) and heterostructures for enhancing CO2RR will be illustrated: (i) single-layer to few-layer MoS2 with vacancies controlled by plasma; (ii) reconstructed edge atoms of monolayer WSe2; (iii) the carbon-doped or carbon-implanted SnS2 nanosheets; and (iv) direct Z-scheme of ZnS/ZIS heterojunctions. Besides the challenges in materials, to make such energy conversion towards practical solutions, some key questions need to be addressed. For instance: Where does the reaction take place and what are the key steps for CO2RR? Nanoscale redox mapping using scanning tunnelling microscope at the TMDC–liquid interface shows layer-dependent redox behavior and also confirms that the edge is the most preferred region for charge transfer. Advancements in in situ and operando synchrotron radiation-based spectroscopies, including X-ray absorption and X-ray photoelectron spectroscopy (XPS), etc., along with various vibrational spectroscopies, such as Raman and Fourier transform infrared spectroscopy (FTIR), have enabled scientists to probe the geometric, bonding and electronic information of the catalyst and obtain atomic insights into the catalytic surfaces and reaction mechanisms.
Brief Bio
Dr. Li-Chyong Chen received her B.S. in Physics from National Taiwan University (NTU) in 1981, and Ph.D. in Applied Physics from Harvard University (1989); afterwards, she worked at the Materials Research Center in General Electric Corporate R&D, Schenectady, New York (1989–1994), before she joined the Center for Condensed Matter Sciences (CCMS), NTU. Li-Chyong was the Director of CCMS (2012-2018), is now the Director of the Center of Atomic Initiative for New Materials (AI-Mat) since 2018, and also a jointly appointed Professor of Physics Department since 2021.
Oct 04, 2022
Hsiang-Yi Yang National Tsing Hua University
Host:
Pao-Ti Chang
Time: 2:20 pm - 3:20 pm
Place: Room 104, CCMS-New Phys. building
Title:
Are the Fermi/eRosita bubbles generated by past activity of the Galactic center black hole?
Abstract
In May 2022, the Event Horizon Telescope has revealed the first image of Sgr A*, the supermassive black hole at the center of our Milky Way Galaxy. Understanding the past activity of Sgr A* has been one of the key questions to address as it will allow us to gain insights into the formation history of the Milky Way. One of the most prominent signature for possible past activity of Sgr A* is the Fermi bubbles, two giant gamma-ray bubbles discovered in 2010. The origin of the Fermi bubbles has been intensely debated; however, in 2020 the newly launched eRosita X-ray satellite has revealed another pair of "eRosita bubbles", providing new constraints on their formation mechanisms. The enormous sizes, symmetries, and properties of the Fermi/eRosita bubbles strongly suggest that they share the same origin. Using cutting-edge numerical simulations including cosmic-ray physics, we show that the Fermi/eRosita bubbles likely originate from past jet activity of Sgr A* about 2.6 million years ago.
Brief Bio
Hsiang-Yi (Karen) Yang is currently an assistant professor and Yushan Young Scholar at the Institute of Astronomy (IoA) of National Tsing Hua University (NTHU). She is a computational astrophysicist, whose research is focused on the formation of galaxies and galaxy clusters using numerical simulations on high performance computing platforms.
Specific areas of her research include black hole feedback in galaxy clusters, the physical origin of Fermi and eRosita bubbles in the Milky Way Galaxy, and cosmic-ray driven galactic outflows.
Oct 11, 2022
Ray-Kuang Lee National Tsing Hua University
Host:
Pao-Ti Chang
Time: 2:20 pm - 3:20 pm
Place: Room 104, CCMS-New Phys. building
Title:
Machine-Learning enhanced Quantum State Tomography and Its Applications
Abstract
With this talk, I will first illustrate the implementation of our machine-learning (ML) enhanced quantum state tomography (QST) for continuous variable, through the experimentally measured data generated from squeezed vacuum states. With the help of ML-QST, we also experimentally reconstructed the Wigner’s quantum phase current for the first time. At the same time, as a collaborator for LIGO-Virgo-KAGRA (LVK) gravitational wave network and Einstein Telescope, our plan to inject this squeezed vacuum field into the advanced gravitational wave detectors will be introduced. Finally, I will report our recent progress in applying such a ML-QST as a crucial diagnostic toolbox for applications with squeezed states, from quantum random number generation, quantum information process, and macroscopic quantum state generation.
Brief Bio
Dr. Ray-Kuang Lee received his BS degree from the department of Electrical Engineering, National Taiwan University (EE/NTU) in 1997, and his MS and PhD degrees from the Institute of Electro-Optical Engineering, National Chiao Tung University (IEO/NCTU), in 1999 and 2004, respectively. From August 2005, he joined the Institute of Photonics Technologies, National Tsing Hua University (IPT/NTHU) as a faculty member and was promoted to the full Professor in August 2013. His research interests cover a wide range of topics on the quantum properties of light, as well as its classical limit. By utilizing Atom-Molecular-Optics (AMO) and Photonics systems as the platform, Dr. Lee has been working on the quantum-classical correspondences between optical and matter waves, the implementation for quantum noise reduction for the advanced gravitational wave detectors, the development for the quantum noise squeezing, and the reflection of an alternative quantum theory. Currently, he is also Professor (Joint Appointment) in the Department of Physics, National Tsing Hua University, Center Scientist of the Physics division, National Center for Theoretical Sciences (NCTS), Board member for KAGRA Scientific Congress (KSC), member of KAGRA Future Strategy Committee and LIGO-Virgo-KAGRA (LVK) Joint Meeting Committee, and the representative of Research Unit of Einstein Telescope (ET). In addition to domestic national projects, Dr. Lee is also the PI for the US Navy Office of Naval Research (ONR) Foreign Research Grant, the US Army Research Office, US Army Combat Capabilities Development Command (DEVCOM), and the Inter-University Research Program from the Institute for Cosmic Ray Research (ICRR), the University of Tokyo.
Oct 18, 2022
Yueh-Ning Lee National Taiwan Normal University
Host:
Pao-Ti Chang
Time: 2:20 pm - 3:20 pm
Place: Room 104, CCMS-New Phys. building
Title:
Non-ideal magnetohydrodynamics in star formation
Abstract
It is now commonly accepted that the formation of the building blocks of our Solar System might have occurred during the early phases of the protoplanetary disk. I will present studies of the self-consistent disk formation starting from the prestellar core collapse. We measure the disk properties, and our findings suggest that 1) the embedded disk structure and dynamics might be (unfortunately) more complicated than we thought and 2) the stellar mass accretion does not necessarily transit through the bulk of the disk as often naturally assumed. The collapse type numerical simulations are computationally challenging and render a wide search of the parameter space unfeasible. During the embedded class 0/1 phase, the close interaction with the envelope should not be neglected when considering the dynamics and evolution of the disk. We proposed a model for self-regulated disk formation, where the magnetic braking is moderated by the non-ideal MHD effects. The resulting disk radius is slowly varying for a wide range of physical parameters, which accounts for the observed small size of young disks. Putting the pieces together, an embedded disk is tightly connected to its envelope, while its global properties are not very sensitive to the prestellar core environment. A simplified view of the young embedded protoplanetary disk might still be possible, while our understanding of the way how a disk is built up within a collapsing envelope awaits further refinement.
Brief Bio
Associate professor at the Department of Earth Sciences and deputy director of the Center of Astronomy and Gravitation, National Taiwan Normal University, Yueh-Ning Lee specializes in numerical modeling of the physics of the interstellar medium. She obtained a doctoral degree in Astronomy and Astrophysics at the Paris Diderot University in 2017. Her main research interest is to understand how star formation is governed by physical processes such as self-gravity, turbulence, and the electromagnetic effects.
Oct 25, 2022
Yu-Ju Lin Institute of Atomic and Molecular Sciences, Academia Sinica
Host:
Pao-Ti Chang
Time: 2:20 pm - 3:20 pm
Place: Room 104, CCMS-New Phys. building
Title:
Vortex nucleations in rotating spinor Bose condensates under synthetic azimuthal gauge potentials
Abstract
The realization of synthetic gauge fields for charge-neutral ultracold atoms has opened new opportunities for creating and investigating topological quantum matters in a clean and easy-to-manipulate environment. One can exploit synthetic gauge potentials to rotate quantum gases and access rich intriguing physical phenomena. Among them, quantized vortices have attracted extensive studies, which also appear in other systems such as helium superfluids, superconductors and neutron stars. We investigate novel phenomena of vortex nucleations in a spinor Bose condensate, which are induced by synthetic azimuthal gauge potentials acting as light-induced effective rotations. We identify the main mechanism of vortex nucleations as the dynamical instability of low-energy excitations. Our experimental data has qualitative agreement with the time-dependent Gross-Pitaevskii equation (GPE) simulations and reveals a novel type of vortex nucleations.
Brief Bio
Dr. Yu-Ju Lin is an associate research fellow in the Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica. Dr. Lin received her PhD degree in Stanford University in 2007, and worked in National Institute of Standards and Technology in Maryland, USA as a postdoc. Dr. Lin’s research interests center on ultracold atomic quantum gases, the Bose-Einstein condensates with spin degrees of freedom. Specifically, she focuses on creating synthetic gauge fields for these charge-neutral atoms, as a quantum simulator for charged particles in real magnetic fields.
Nov 01, 2022
Hikaru Kawai Department of Physics, National Taiwan University
Host:
Pao-Ti Chang
Time: 2:20 pm - 3:20 pm
Place: Room 104, CCMS-New Phys. building
Title:
Is it possible to see the Planck scale?
Abstract
The fundamental interaction between elementary particles consists of four forces: the electromagnetic force, the strong force, the weak force, and gravity. At distances reachable by current accelerators, gravity is extremely smaller than the other three forces. However, at a hypothetical short distance, called the Planck scale, all forces are equal in magnitude. In other words, something with the size of the Planck scale seems to underlie everything, and a strong candidate for this is string theory. In this talk, I will discuss the possibility of actually seeing physical phenomena at the Planck scale, including string theory.Specifically, we plan to discuss (1) the emergence and expansion of the universe based on the matrix model, (2) the naturalness problem and the behavior of the Standard Model at the Planck scale, and (3) the relationship between black hole evaporation and the Planck scale.
Brief Bio
Prof. Hikaru Kawai is a world-renown theoretical physicist. He has made many important contributions to high-energy physics, including string theory, field theory, and particle physics. After obtaining his Ph.D. degree from the University of Tokyo in 1983, he was an assistant professor at Cornell University (1984 - 1988), and then as an associate professor at the University of Tokyo (1988 - 1993). He was a full professor at KEK (1993 - 1999), and then at Kyoto University (1999 - 2021). He has won the Nishina Memorial Prize (1984), the Presidential Young Investigator Award (1988), the Particle Physics Medal (2006), etc. Since Apr. 2021, he is a Chin-Yu chair professor at the Center for Theoretical Physics at National Taiwan University.
Nov 08, 2022
Pik Yin Lai Department of Physics, National Central University
Host:
Pao-Ti Chang
Time: 2:20 pm - 3:20 pm
Place: Room 104, CCMS-New Phys. building
Title:
Recent Progress in Non-equilibrium Statistical Physics: manipulating the Brownian particles
Abstract
As we know, the second law of thermodynamics or non-decreasing of entropy implies the "arrow of time", which states that macroscopic non-equilibrium processes are irreversibility. But the microscopic laws of physics are all time-reversible. This apparent contradiction, known as the Loschmidt's paradox, has troubled scientists more than hundred years. The fallacy was largely due to the overlook of unobserved degrees of freedom, such as in the thermal bath. On the other hand, modern techniques allowing the miniaturization of systems and devices to observe fluctuations in microscopic scales and theoretical breakthrough in Fluctuation Relations, open up the era of modern non-equilibrium statistical physics. In this talk, I will briefly discuss the development and breakthrough in non-equilibrium statistical physics in recent years. Some descriptions of my theoretical research together with collaborations with experimental colleagues will also be presented.
Brief Bio
Prof. Pik-Yin Lai received his B.S. degree in Hong Kong University in 1983 with first class honor and Ph. D. in physics at the University of Pittsburgh in 1988. He was then a postdoctoral researcher in University of Georgia and University of Pittsburgh. From 1990 to 1992, he was a research scientist in the Institute of Physics of Mainz University at Germany. He then joined the faculty of the Physics Department of National Central University in Taiwan and was a full professor since 1996. He has served as the director of the Center for Complex Systems, director of the Graduate Institute of Biophysics and the Head of the Physics department, and currently is the University Chair Professor in Physics. Prof. Lai’s research has been focused on various areas including biophysics, soft-matter physics, statistical physics, nonlinear physics and complex systems, with both theoretical and experimental approaches and has published over 200 scientific papers. He has received the National Science Council outstanding research award and other honors such as Elected Fellow of the Physical Society of Taiwan.
