Fall 2023 Colloquium Schedule
Time: Tuesdays 3 pm to 4 pm. Refreshment starts at 2:45 pm
Venue: 25 Park Place Room 223 and Room 2608
Colloquium contact: Yang-Ting Chien ([email protected]) and Viacheslav Sadykov ([email protected])
*Thursday
Date |
Speaker |
Title and Abstract |
Aug 22 | First Week of Semester | |
Aug 29 | Introductory Colloquium | Poster Presentations 1 |
Sep 5 | Introductory Colloquium | Poster Presentations 2 |
Sep 12 |
Manasvi Lingam (Florida Institute of Technology) Host: Idan Ginsburg Room 223 |
(Sub)Stellar constraints on the habitability of exoplanets
With the rapidly expanding number of exoplanets, understanding the manifold factors that shape (exo)planetary habitability has become increasingly significant. Although habitability is regulated by many planetary parameters, there is growing evidence that the host (sub)stellar object plays a major role in this context. I will outline the research undertaken with my collaborators in the following areas: (1) atmospheric escape mediated by stellar winds and space weather (flares and coronal mass ejections); (2) synthesis of vital prebiotic molecules by UV radiation and/or stellar energetic particles; and (3) potential characteristics of extraterrestrial photosynthesis. Along the way, I will sketch some of the unresolved questions and topics that warrant further study. |
Sep 19 |
Ian Ferguson (Kennesaw State University) Host: Unil Perera Room 223 |
Is Quantum Information (QI@RT) Room Temperature possible?
There is an increasing interest in materials and devices for quantum information (QI) for future computing needs, which are not met using conventional electronics. Quantum computing could enhance the functionalities, storage capabilities, and data manipulation and transmission, for the next generation of devices. Spintronics is an enabling technology to meet the speed, power, and scalability requirements for quantum information. Spin of a material is directly related to magnetic, electrical, and optical properties. However, most materials show conducive properties for spintronics only at cryogenic temperatures, which limits their practical applications. There is a need to investigate spintronic materials for these applications at room temperature (RT).Gallium nitride doped with transition metal or rare earth elements has the potential for controllable spin and charge for spintronics at RT. Gadolinium-doped GaN grown using MOCVD has been shown to have ferromagnetism at RT that is intrinsic and free-carrier mediated from vibrating sample magnetometry and Anomalous Hall effect (AHE) measurements. However, only GaGdN grown using a precursor, which contains oxygen in its organic ligand that is incorporated in the GaGdN exhibited ferromagnetism. Density functional theory calculations show that elements such as oxygen and carbon can introduce localized states near the Fermi level of GaGdN that couple with Gd states and cause p-d hybridization of the p-orbitals of O or C with the d-orbitals of Gd atoms to result in the ferromagnetism. It is necessary to understand the role of O and C in the magnetic properties of GaGdN to be able to control and manipulate its spin. Magnetic, structural, and electrical properties of GaGdN grown with different chemistries and implanted with O or C are investigated in this work in order to gain a better understanding of the origin of ferromagnetism in GaGdN. Understanding of the mechanism for RT ferromagnetism in GaGdN is essential to control the spin and build practical spintronic devices for quantum information applications at room temperature (QI@RT). |
Sep 26 |
Andreas Papaefstathiou (Kennesaw State University) Host: Yang-Ting Chien Room 223 |
Imprints of Electro-Weak Symmetry Breaking at Colliders
With the next generation of collider experiments, we possess the unique opportunity to comprehend some of the most profound scientific questions on the nature of matter and its interactions. In particular, the Higgs field and the electro-weak phase transition link several open mysteries together, intertwining collider measurements with cosmology and astrophysics. In this talk, I will explain the origin of these connections and explore their phenomenological implications. I will focus on the simplest realizations of such phenomena, scalar extensions of the Standard Model, discussing discovery prospects at current and future colliders. |
Oct 3 |
Jianming Wen (Kennesaw State University) Host: Sidong Lei Room 223 |
Harnessing Single Photons and Neutral Atoms: Advancing Quantum Information Science and Technologies through Entanglement Generation
Quantum information science stands at a transformative crossroads, poised to revolutionize diverse fields such as computing, cryptography, communication, networks, metrology, sensing, and imaging. Among various quantum systems, single photons and neutral atoms shine as pivotal catalysts for this quantum revolution. This presentation explores the synergistic convergence of these platforms, with a central focus on pioneering narrowband entangled biphoton sources via spontaneous four-wave mixing (SFWM) in coherent atomic ensembles. Notably, we’ve recently achieved the unique feat of creating a reliable W-class triphoton source through spontaneous six-wave mixing (SSWM) in hot atomic vapor. Our journey commences with foundational quantum concepts, surveys alternative qubit platforms, and dives into conventional biphoton generation methods like spontaneous parametric down-conversion (SPDC) and SFWM in solid materials. We unveil our recent breakthroughs in narrowband bi- and tri-photon generation within coherent atoms, promising long-distance quantum information processing and networking. Single photons, embodying unshakeable quantum properties, serve as versatile information carriers, while neutral atoms offer an ideal setting for nurturing long-lived qubits and quantum memory. We demystify the intricate mechanisms underlying entanglement generation with neutral atoms, shedding light on SFWM and SSWM principles. The talk concludes by showcasing our latest advancements, highlighting our capacity to generate unparalleled coherence and tunability in narrowband entangled photons. These attributes propel scalable quantum networks, connecting quantum processors and enabling secure global information exchange. As we embark on this enlightening journey, we illuminate the pivotal roles of single photons and neutral atoms in advancing quantum information science and technologies, inspiring fresh research avenues toward a quantum-enabled future. |
Oct 10 |
Feryal Ozel (Georgia Institute of Technology) Host: Yang-Ting Chien Room 223 |
We got black hole images. Now what?
The data collected with the Event Horizon Telescope provided the first horizon-scale images of two nearby supermassive black holes. A tremendous amount of theoretical modeling and interpretation, including large simulation libraries and new analysis tools, were necessary to extract physical constraints from these images and perform quantitative tests of General Relativity, plasma physics, and black hole environments. In this talk, I will discuss: 1. the physics behind the simulations and where they succeeded and failed; 2. new directions in plasma astrophysics that are necessary to go beyond the current state-of-the-art; and 3. how the simulation libraries and machine-learning approaches have, in turn, helped us make better black hole images. |
Oct 17 |
Adam Wax (Duke University) Host: Unil Perera Room 223 |
Quantitative phase imaging of nanoscale ultrastructure for analyzing mechanical properties of live cells
The nanoscale ultrastructure of cells can be analyzed using quantitative phase imaging to examine variations in refractive index. By studying cell response to subtle mechanical stimuli, these refractive index variations can be related to viscoelastic properties using parameters such as disorder strength. Comparative studies show that these measures can also be related to shear modulus as determined by atomic force microscopy, a standard tool for mechanobiology. In contrast, the spatial organization of these variations is typically characterized using fractal dimension which is also seen to increase with cancer progression. Our recent work has linked these two measurements using multiscale measurements of optical phase variance to calculate disorder strength and in turn to determine the fractal dimension of the structures. Disorder strength is seen to vary with imaging resolution with fractal dimension revealed in the observed trends over length scale. Studies will be presented which enable distinction of cell phenotype using these two parameters while their combined use presents a new approach for better understanding cellular restructuring. Finally, modulation of these parameters is examined as a means to study early carcinogenic due to heavy metal exposure. |
Oct 24 |
Gongjie Li (Georgia Institute of Technology) Host: Yang-Ting Chien Room 223 |
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Oct 31 |
Marina Kounkel (University of North Florida) Host: Viacheslav Sadykov Room 223 |
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Nov 1 |
KD Leka (NorthWest Research Associates) Host: Viacheslav Sadykov Room 223 |
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Nov 14 |
TBD Host: |
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Nov 21 | Thanksgiving Week | |
Nov 28 |
Megan Connors (Georgia State University, Physics and Astronomy) Host: Sebastien Lepine Room 223 |
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Dec 5 | Final Exam Week Starts / No Colloquium |
Spring 2023 Colloquium Schedule
Time: Tuesdays 3 pm to 4 pm. Refreshment starts at 2:45 pm
Venue: 25 Park Place Room 223 and Room 2608
Colloquium contact: Yang-Ting Chien ([email protected]) and Viacheslav Sadykov ([email protected])
*Thursday
Date |
Speaker |
Title and Abstract |
Jan 10 | First Week of Semester | |
Jan 17 | Second Week of Semester after MLK Day | |
Jan 24 |
Shan Wu (Lawrence Berkeley National Lab) Host: Mike Crenshaw Room 2608 |
Magnetic switching resistance materials
Quantum materials are complex systems in which electrons interact strongly and collaboratively. As such, quantum mechanics is dominant in the versatile materials that allow us to explore emergent quantum phenomena and their potential applications in future technologies. Emergent quantum materials embrace material properties that demonstrate the significance of interplay among multiple dimensions in the system. These exotic properties can be harvested into applications for next-generation quantum technologies. Antiferromagnetic (AFM) spintronics is among the newest of quantum technologies, which realize the manipulation of spin-transport in antiferromagnets for memory devices. Recently, the intercalated transition metal dichalcogenide (TMD) antiferromagnet Fe1/3+δNbS2 has shown relevant spintronic features, namely, resistance switching. The original explanation of AFM switching hypothesized that it was driven by a coexisting spin glass phase. Here, I will present our discovery of highly tunable antiferromagnetic orders and discuss how they relate to the observed resistance switching in this material. The rapid change of the magnetic states underlies the sensitive switching behaviors, providing crucial insights on the magnetic ground states that form the basis for understanding the fascinating spintronic behavior. I will also talk about my recent work on this system and open opportunities in the intercalated TMDs as part of the exploration of the spintronic materials. |
Jan 26* |
Kun Wang (Mississippi State University) Host: Mike Crenshaw Room 223 |
Probing Quantum Transport and Energy Conversion at the Molecular Scale
Molecules – the smallest unit of matter – have been playing a pivotal role in today’s materials science, nanotechnology, and quantum science. The capability to manipulate physical and chemical behaviors of single molecules and understand how they respond to external stimuli represents important opportunities for optoelectronics, energy, and quantum applications. In this colloquium, I will talk about my recent studies on developing experimental tools to probe quantum transport in molecular-scale systems and further leveraging them to address challenges in molecular electronics, energy conversion, and nanosensing. First, I will introduce strategies to construct molecular-scale electronic devices, such as diodes and transistors. Second, I will discuss my work on developing new experimental approaches to interrogate thermoelectric energy conversion in molecular junction devices, which points to new opportunities for energy harvesting and refrigeration. Third, I will describe how single molecules can be used as nanoscopic quantum sensors to directly access plasmonic hot carriers and how the experimental approach developed in my work will enable systematic study of plasmon-driven processes in many plasmonic and nanophotonic systems. Finally, I will give an overview for my future research directions. |
Jan 31 |
Jay Mathews (University of Dayton) Host: Mike Crenshaw Room 223 |
At the lasing threshold: Germanium-tin as a gain medium for silicon-based lasers
Silicon is the basis for a multi-billion dollar industry, but its optical properties have limited its use in optoelectronics for infrared (IR) applications. There are a number of applications that could benefit from low-cost Si integrated photonics including photovoltaics, infrared detection and imaging, optical interconnects (OICs), and photonic integrated circuits (PICs). In particular, Si-based OICs and PICs require efficient laser sources, modulators, low loss waveguides, optical switches, and photodetectors, all of which must be integrated into a single Si chip using complementary metal-oxide-semiconductor (CMOS) processing. The biggest gap in technology at the moment is the development of an on-chip light source. One possible solution is to use GeSn alloys as a gain medium for laser devices. These thin films are grown on Si substrates and compatible with standard Si processing techniques, they have band gaps in the infrared, and the band structure of GeSn yields more efficient optical absorption and emission than that in Si. These unique properties have prompted a recent effort to develop optoelectronics from GeSn films, and this research has resulted in a number of prototype photonic devices such as photodetectors that cover all telecommunications wavelengths, infrared light-emitting diodes, and optically-pumped waveguide lasers. However, GeSn waveguide devices have only demonstrated lasing at cryogenic temperatures without complicated strain-inducing structures. In this talk, I will present recent work on the fabrication and characterization of waveguide devices made from GeSn alloys and subjected to optical pumping at room temperature. Based on the results, an emission model was developed to predict the optical emission characteristics based on the material properties, waveguide geometry, and experimental conditions. The model was used to explain the emission data from the GeSn waveguides, and it was compared to other recent GeSn waveguide experiments. I will present details of the modeling, along with some predictions on how room temperature lasing could be achieved in GeSn waveguides. |
Feb 2* |
Yulia Maximenko (National Institute of Standards and Technology) Host: Mike Crenshaw Room 2608 |
Flatland quantum simulation and visualization with atomic resolution
Quantum computing and simulation promise to revolutionize fundamental physics, technology, and quantum chemistry. Simulating quantum systems using analog platforms was first proposed in the 1980s, but recent technological advances have brought this idea to new heights. Trapped atoms and ions, superconducting circuits, and advanced solid-state platforms have achieved an unprecedented level of quantum control and are able to model increasingly complex Hamiltonians. Quantum simulation in 2D solid platforms has proved to be incredibly versatile, while also being compatible with the existing semiconductor technology. In this colloquium, I will showcase the exciting recent developments in the field of 2D quantum simulators, highlighting twisted moiré systems and atomic manipulation. Scanning tunneling microscopy (STM) has proved crucial for the progress of this field. My focus will be on revealing the topological and strongly correlated physics in twisted layered graphene and on the surprising insights gained through the use of STM. Through high-resolution magnetic field scanning tunneling spectroscopy, we have demonstrated the importance of the fine details of quantum geometry in these novel 2D platforms. Specifically, I will report on the discovery of an emergent anomalously large magnetic susceptibility caused by the band topology in twisted double bilayer graphene. |
Feb 7 | No colloquium | |
Feb 14 | No colloquium | |
Feb 21 |
Chen Shi (University of California, Los Angeles) Host: Petrus Martens Room 2608 |
Understanding the solar corona and wind in the epoch of Parker Solar Probe
The outflow of hot plasma from the solar corona, including the more continuous solar wind and the bursty plasma expulsions called Coronal Mass Ejections (CMEs) are the main drivers of space weather. The solar magnetic field, driving the cavity in the interstellar medium in which all planets are embedded, stores and releases a significant amount of energy into the interplanetary space. Understanding the origin and dynamical processes associated with the generation of the solar corona, the acceleration of the solar wind and its ongoing turbulent dynamics are some of the most important tasks of space physics. After decades of exploration fundamental questions concerning the physical processes underlying the origin of the solar corona and solar wind acceleration remain. Two of the most outstanding topics are magnetic reconnection in the solar corona and turbulence in the solar wind. As Parker Solar Probe lowers its orbit into regions close to the Sun never observed directly previously, many novel observations have been made. In this seminar, I will review recent progress on the theory, modeling, and observations of the solar wind. I will discuss opportunities and challenges within the context of current and future missions, including the presently flying, from Parker Solar Probe to Solar Orbiter as well as future in situ exploratory missions such as HelioSwarm. |
Feb 28 |
Luiz Santos (Emory University) Host: Yang-Ting Chien Room 2608 |
Interplay of Interactions and Topology in Electronic Fractals Rapid theoretical and experimental progress in characterizing phases of matter has brought to light a plethora of new topological phases. A remarkable example arises in two-dimensional crystals, where electrons are subject to an external magnetic field. This iconic system supports a rich structure of fractal electronic bands with topological properties that are traditionally linked to the quantum Hall effect, but only recently have been realized in the burgeoning class of moiré crystals. While the non-interacting properties of fractal bands have long been classified, the interplay of interactions and band topology remains a much uncharted territory. In this colloquium I will discuss new quantum behavior that emerges from the interplay of interactions and the self-similar character of fractal bands formed in the presence of large magnetic fluxes. I will present universal results concerning quantum phase transitions and interaction driven electronic orders in fractal bands. Among these are new classes of unconventional superconductors (including topological ones) that fall outside the paradigm of phonon-mediated superconductivity. Fractal electronic bands thus represent rich platforms to explore novel quantum phases of matter. |
Mar 7 |
Lulu Zhao (University of Michigan) Host: Petrus Martens Room 2608 |
Space Radiation Environment
Space Weather is the physical and phenomenological state of natural space environments. One important component of the space weather is the space radiation. Space radiation refers to high-energy ionized particles of different origin present in space are of great concern for aviation, satellites and biological systems. It covers mainly the galactic cosmic ray (GCR) background, solar energetic particle (SEPs) and the Earth’s trapped radiation belts. SEPs are not only a major component of space radiation, but their intensity and energy spectra dramatically change in short periods of time. In fact, the space radiation hazard is one of the major unsolved problems (“tall poles”) hindering space travel beyond low-Earth orbit.SEPs are suggested to be accelerated to high-energy either by magnetic reconnection-driven processes in solar flares or by shocks driven by coronal mass ejections. SEPs can be accelerated up to tens of GeV, and the flux of >10 MeV protons could exceed their background level by several orders of magnitude. Protons of >150 MeV are very difficult to shield, and the sparsity and large variation of the SEP events make them difficult to predict. Many efforts have been made to predict the SEPs using both physics-based approaches and machine learning methods. In this presentation, I will discuss the current status and future visions of the space radiation prediction. |
Mar 9* |
Xiaocan Li (Dartmouth University) Host: Petrus Martens Room 2608 |
Modeling Particle Acceleration and Transport in Solar Flares
Solar flares are among the most explosive and dynamic events in our solar system. These phenomena release massive amounts of energy and can accelerate a large number of particles to very high energies. As these particles can significantly impact our technology and human activities, it is crucial to understand how they are accelerated during solar flares. However, this task is challenging due to the vast and complex nature of solar flares. In recent years, an emerging framework combining theory, numerical modeling, and observations has made significant progress toward understanding particle acceleration during solar flares. In this talk, I will summarize those made by modeling, including kinetic particle-in-cell simulations to study small-scale physics and macroscopic modeling to investigate large-scale processes. By combining these results with observations, we have gained important insights into particle acceleration and transport during solar flares. I will also highlight the challenges in understanding complex physics and interpreting modern high-resolution observations using massive numerical simulations. I will discuss current and future efforts aimed at addressing these challenges. This research area is highly active and exciting, offering numerous opportunities for discovery and impact. |
Mar 14 | Spring break | |
Mar 21 |
Student flash talks Host: Sebastien Lepine Room 2608 |
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Mar 28 |
Ian Ferguson (Kennesaw State University) Host: Unil Perera (Rescheduled to Fall 2023) |
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Apr 4 |
Paul Charbonneau (Université de Montréal), Nelson Speaker Host: Petrus Martens Room 223 |
Avalanches, earthquakes and solar flares
Avalanches, earthquakes and solar flares; beside posing a threat to human societies and infrastuctures, what could these three natural phenomena possibly have in common? They unfold on widely different spatial scales, from hundreds of meters for a snowslope, hundreds of kilometers for a seismic fault, up to tens of thousands kilometer for a solar active region. Moreover, their internal dynamics relies on very different physics: friction between snowflakes, elastic deformation or rock, and dissipation of electrical currents. One key commonality, however, is that all three are natural systems that accumulate energy very slowly, but release it in a strongly intermittent and scale-invariant manner. In this talk I will discuss a physical modelling paradigm whereby such natural complex systems and phenomena emerge from a great many simple dynamical elements interacting locally with one another at scales much smaller than the global scale of the system. Complexity thus emerges from simplicity! In illustrating and explaining these ideas, the emphasis will be placed on solar flares, these being one of the major drivers of space weather. |
Apr 11 |
Sonny Mantry (University of North Georgia) Host: Yang-Ting Chien Room 223 |
Jets as Standard Candles for Particle Physics at Colliders
Jets correspond to highly collimated sprays of energetic particles that emerge from high energy collisions using beams of electrons, protons, or heavier nuclei. Jets are an emergent phenomenon arising from the structure and dynamics of gauge theories such as Quantum Chromodynamics. They serve as beacons for hard interaction processes involving quarks, gluons, and the production of heavy resonances. Understanding the structure, substructure, and dynamics of jets is essential for uncovering hints of new physics, the interactions of elementary particles, and the structure of nucleons and nuclei.In this talk, I will give a pedagogical introduction to the physics of jets, followed by an overview of recent theoretical developments. I will also discuss a few recent applications of jet analyses, including precision extractions of the top quark mass, using jet-based global event shapes as a probe of nuclear structure and dynamics, probing nucleon structure using the electric charge of jets, and exploring the possibility of exotic processes such as charged lepton flavor violation. |
Apr 18 |
Misty Bentz (Georgia State University, Physics and Astronomy) Host: Sebastien Lepine Room 223 |
Comparing Direct Black Hole Mass Measurements in Active Galactic Nuclei
Supermassive black holes appear to be ubiquitous in galaxy nuclei, and several large-scale galaxy properties have been to found to scale with black hole mass, giving rise to the idea that galaxies and their black holes likely co-evolve. There are only a few techniques that can directly constrain the mass of a black hole through its gravitational influence on luminous matter, of which the most commonly applied are reverberation mapping and stellar or gas dynamical modeling. These techniques have been applied to a modest number of black holes, with the vast majority of black hole masses in the literature instead being estimates derived from scaling relationships that are based on these direct results. In the local universe, these scaling relationships are derived from dynamical modeling results, while outside the local universe, reverberation mapping results provide the foundation for different scaling relationships. However, there are only a handful of black holes with masses that have been constrained through multiple techniques because of their disparate technical requirements. When it comes to accreting supermassive black holes, the situation is even worse because they are rare and most are too far away to allow the spatial resolution needed for dynamical modeling. I will describe our ongoing project to directly compare black hole masses from reverberation mapping and stellar dynamical modeling in the nearest Type 1 Seyferts. Both reverberation mapping and stellar dynamical modeling are time- and resource-intensive techniques and the number of galaxies we can study is small, but the results will help uncover potential biases in these direct mass techniques and illuminate any differences in the black hole mass scales that are applied locally versus at cosmological distances. |
Apr 25 | Final Exam Week Starts / No Colloquium |
Fall 2022 Colloquium Schedule
Time: Tuesdays 3 pm to 4 pm. Refreshment starts at 2:45 pm
Venue: 25 Park Place Room 223
Colloquium contact: Yang-Ting Chien ([email protected]) and Viacheslav Sadykov ([email protected])
*Thursday