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Colloquium Archive

Colloquium Archive

Spring 2024

Host: Joseph Tischler

Title: "Towards Non-Blinking Strongly Confined Perovskite Quantum Dots"

Abstract: Quantum information science has shown its capabilities to enable secure quantum communications. Single photon emitters that emit photons one at a time are fundamental elements of such transformative technologies. Colloidal cesium lead halide (CsPbX3, X=Br, I) perovskite quantum dots are ideal for next-generation single photon emitters because of their high room-temperature luminescence efficiency and low-cost, scalable syntheses. Unfortunately, individual perovskite quantum dots show insufficient photostability and severe photoluminescence intensity fluctuations (also called blinking). One major roadblock toward non-blinking, photostable perovskite quantum dots is their highly ionic crystal structure. When preparing single perovskite quantum dot samples, quantum dot colloids often need to be diluted. During this process ligands can detach from the quantum dot, introducing defects. This is particularly detrimental to strongly confined perovskite quantum dots since exciton-surface lattice interaction is greatly enhanced.

To suppress perovskite quantum dot blinking and photodegradation, we embedded quantum dots in an organic crystal matrix consisting of Phenethylammonium bromide (PEABr) salts. The bromide rich surface of a quantum dot can be epitaxially anchored onto the PEABr crystals and therefore be stabilized. Individual strongly confined CsPbBr3 quantum dots in our matrix show nearly non-blinking behavior under non-resonant laser excitations at room temperature. These quantum dots remain photostable without photoluminescence intensity decrease and spectral shift after more than 12 hours of continued excitations. We anticipate that those quantum dots  will lead to more accurate and detailed study of exciton dynamics and structural-optical property relationships in this important class of materials.

Host: Brad Abbott

Title: "Computing for Large High Energy Physics Experiments with a Focus on CMS"

Abstract: Computing is necessary for high energy experiments. Data collected from experiments grows year to year until it is too large to fit on one singular machine, and those single machines cannot handle the computation required to perform analysis on this data. In order to do analysis at this massive scale we can use a grid system that stores the data on disks. A grid system is working to network computers in a flexible and scalable architecture. Instead of one computer we are now connecting two and then three and then as many as we can. We also want to be able to archive the data and we do that through a tape system. In this talk we explore how we not only use grid systems, but also how data is stored.

Host: Sean Matt

Title: "Young Protostellar Disks and Their Asymmetric Environments Set the Stage for Planet Formation"

Abstract: Evidence that planet formation begins when protostars are less than 1 million years old continues to build. During this early phase of star formation, protostars and their disks are still embedded in (and feeding from) their natal environments at a time when I have demonstrated that the first steps of planet formation occur. In particular, streamers---long and narrow infalling channels that funnel material to disks from their environments---have been predicted theoretically and serendipitously observed in a variety of tracers.  In this talk I will outline the various ways streamers can influence the star and planet formation process and describe my current research and plans to probe how asymmetric infall from the larger-scale environment influence disk structure, temperature, and chemistry.  These disk properties are directly connected to when planets form, where, and with what composition. Despite the growing evidence that the larger scale environments have an influence on the youngest planet-forming disks, my PRODIGE survey, carried out with the NOEMA interferometer, is the first and only large observing program specifically designed with streamers in mind. Results from my observations with the PRODIGE survey pave the way for more-detailed observations targeting the initial conditions of planet formation.

Host: Sean Matt

Title: "Galactic Archaeology: the Formation and Evolution of the Milky Way"

Abstract: Our understanding of the Milky Way is in the midst of a revolution through the combination of large-scale spectroscopic surveys such as APOGEE and GALAH along with the Gaia satellite providing information on billions of stars across the Galaxy. I will give an overview of the current chemodynamic structure of the Milky Way from these surveys, ranging from the bulge to the edge of the disk, and outline the key physical processes that have governed the evolution of our Galaxy. I will describe our state-of-the-art chemical evolution models, which are the first to be able to match the detailed chemical structure across the Milky Way. I will also demonstrate how the Milky Way can be used as a benchmark for galaxy evolution, outlining a new technique that enables direct comparisons of our Galaxy to external galaxies for the first time. I will highlight future applications of these analysis techniques, including to our upcoming large ESO-MUSE program GECKOS. GECKOS will deliver MUSE observations of 35 edge-on galaxies with unprecedented depth and spatial coverage, providing detailed kinematic and stellar population measurements beyond the equivalent of the solar neighborhood in these galaxies.

Host: Sean Matt

Title: "Tidal disruption events: unresolved problems, challenges, and future prospects"

Abstract: What happens if a main-sequence star orbits very close to a supermassive black hole in a galactic center? If the star approaches within tens of times the event horizon of the black hole, the black holes's intense tidal forces would tear the star apart in a matter of hours. This dramatic event, also known as a tidal disruption event, may sound like a Sci-Fi movie. However, since its first detection in the 1990s, the number of detected events have been steadily growing thanks to ongoing surveys and telescopes, such as Pan-STARRS, ASAS-SN, and ZTF, reaching approximately one hundred. The prospect of future surveys and advanced telescopes, exemplified by the Vera C. Rubin Observatory, promises a surge in detections by several orders of magnitude over the next decade. These events offer a unique opportunity to enhance our understanding of the population of dormant massive black holes, which are otherwise challenging to identify, and distant galactic centers that can not be directly resolved. However, as the observational catalog expands, our theoretical understanding lags behind, struggling to elucidate various features unveiled by detected events. In this talk, I will address some of the unresolved problems of tidal disruption events, along with relevant challenges and emerging frontiers crucial to advancing our comprehension. I will present the results of my efforts to address these long-lasting problems with various methods, including relativistic hydrodynamics simulations and stellar evolution calculations. Lastly, I will discuss promising future directions and numerous opportunities in this field.

Host: Sean Matt

Title: "Revealing the Hidden Gaseous Ecosystem Around Galaxies over 10 Billion Years"

Abstract: The star formation history of the universe reveals that galaxies most actively build their mass at "Cosmic Noon", roughly 10 billion years ago, decreasing towards present day. The inflow and outflow of gas between galaxies and their surroundings drives this evolution, both fueling and quenching the formation of stars. These gas flows pass through and contribute to the vast reservoir known as the circumgalactic medium (CGM). While the CGM contains over 50% of a galaxy's non-dark matter mass, its diffuse nature makes it difficult to observe directly. In this talk, I will discuss two methods for studying this gas: (1) Quasar absorption lines. I will describe the absorbing CGM at low redshift before stepping back in time to Cosmic Noon where I am leading a survey to characterize the CGM when it is most influential for galaxy evolution yet still largely unexplored. (2) Direct emission mapping. CGM science is now stepping into a new era where I can directly track gas between galaxy disks and their CGM in emission. I will present ultra-deep emission maps of the CGM around a nearby starbursting galaxy. Observations such as these are a key discovery area for galaxy evolution science in the next decade.

Host: Sean Matt

Title: "Galaxy formation: the key physical processes involved, how we model them, and how to best test models"

Abstract: Understanding the physics of galaxy formation has been a central goal of astrophysicists for decades. Though we have made significant progress, there is more work to be done. I will describe what makes understanding galaxy formation so challenging. I will detail how theorists work to decipher this puzzle using numerical simulations, highlighting the key physical processes involved. I will then discuss the idea of 'forward modeling', i.e. predicting synthetic observables from hydrodynamical simulations in order to more directly confront theory and observation. Finally, I will present a recent controversial claim, that observations of too many bright galaxies in the early universe have "broken cosmology." I will demonstrate that if one accurately models the physics of stellar feedback and carefully forward-models observables, this tension disappears.

Host: Thirumalai Venkatesan

Title: "Quantum Magnetic Sensing and Imaging using Nitrogen-Vacancy Centers in Diamond"

Abstract: I will describe my work on high-resolution quantum magnetic imaging with nitrogen-vacancy (NV) centers in diamond to solve previously-unsolvable technical problems. After introducing the motivations and techniques, I will present several case studies on passively interrogating the magnetic fields from electric currents in electronics and integrated circuits. Magnetic sensing is an appealing tool because it allows us to measure weak magnetic sources deep within otherwise-opaque materials, and magnetometers based on quantum sensing can often achieve performance specifications that are difficult to reach with classical sensors. After summarizing my ongoing work using NV magnetic imaging for electronics troubleshooting and counterfeit protection, I will conclude by outlining the anticipated near-term directions and challenges for quantum magnetic imaging.

Host: Sean Matt

Title: "Probing Cosmic Structure Evolution with Galaxy Clusters"

Abstract: Our understanding of the Universe is at a critical juncture.  For decades, the standard model of cosmology based on general relativity, dark matter, and dark energy (ɅCDM) has passed many experimental tests.  However, the recently emerged S8 tension — the discrepancy between the density fluctuation parameter measured by early- and late-universe probes — has the potential to challenge ɅCDM.  In this talk, I will discuss how we use galaxy clusters to measure the evolution of S8 and to probe the nature of gravity at cosmological scales.   I will talk about how we use observations across the electromagnetic spectrum to understand the astrophysics of clusters, which in turn makes clusters better cosmological probes.  I will also discuss how we plan to combine galaxy clusters with other cosmological probes to measure the growth of cosmic structure and address the S8 tension.

Host: Mukremin Kilic

Title: "Planetary Systems around White Dwarfs"

Abstract: Planetary systems are common around main sequence stars. However, there is little knowledge about their fate once the star evolves off the main sequence. In this talk, I will present various efforts to search for planets around white dwarfs. Currently, four planetary-mass objects have been detected around white dwarfs using four distinctive techniques. Additionally, I will discuss how planetary systems around white dwarfs can be utilized to constrain the chemical composition of extrasolar planetesimals -- the building blocks of extrasolar planets. Looking ahead, there are several on-going and planned telescope projects that can further our understanding of planetary systems around white dwarfs.

Host: Bruno Uchoa

Title: "Measurement and feedback induced phase transitions in open quantum many-body systems"

Abstract: The ability to control and measure properties of quantum many-body systems has reached a new level of experimental accuracy. The dynamical states that emerge in these systems can be theoretically characterized by their entanglement structure. Generically, the unitary time evolution of a quantum many-body system couples its microscopic constituents leading to a highly entangled quantum state. On the other hand, performing a global measurement to learn something about the physical content of the system will collapse the wavefunction, destroying any entanglement. However, if a quantum system undergoing unitary time evolution is measured locally at a small but non-zero rate, it was recently discovered that the highly entangled state survives. Only after a critical measurement rate will the wavefunction essentially collapse leading to a measurement induced phase transition in the structure of the entanglement. This talk will discuss the recent progress in our understanding of this measurement induced phase transition in a wide array of open quantum many body systems.  The effects of a conservation law, disorder in the qubit design, and feedback from the measurement outcomes will be discussed.

Host: Eric Abraham

Title: "Atom Interferometry on Earth and in Space"

Abstract: Atom interferometers are a type of quantum sensor useful for navigation, geophysics, and tests of fundamental physics. We report on recent progress in three areas: a trapped-atom Sagnac interferometer for rotation sensing, the use of atom interferometry to measure "tune-out wavelengths" with application to interpreting parity violation in the Standard Model, and a demonstration of atom interferometry in the Cold Atom Laboratory on the international Space Station. These efforts are representative of the types of efforts begin pursued in the field, including pushing towards practical applications, pursuing basic science, and technology demonstrations to support future applications and science.

Fall 2023

Host: Xinyu Dai

Title: "Strong Observational Constraints on the Structure of Quasar Continuum Sources"

Host: Madalina Furis

Title: "Magneto-optics in the Unique 25T Split-Florida Helix Magnet"

Host: Joseph Tischler

Title: "Semiconductor Moiré Superlattices: a New Material Platform for Quantum Information Science "

Host: Sean Matt

Title: "From the surface rotation of stars to their interiors, magnetism, and beyond"

Abstract: Open clusters, such as the Pleiades, Praesepe, and the Hyades, are critical benchmarks for calibrating stellar properties such as rotation and magnetic activity. As stars approach the main sequence, they contract and spin more rapidly; once they reach the main sequence, they stop contracting and their spin speed decreases over time. This spin-down is caused by angular momentum lost via stellar winds, but details of stellar wind torques and any internal angular momentum transport are still uncertain. I will discuss recent results constraining the rotation of old, low-mass stars along with young, solar-mass stars. I will show how we can use new data with a statistically robust fitting method to distinguish between models of stellar rotational evolution.

Host: Howie Baer

Title: "Building the case for future explorations at the Energy Frontier"

Host: Mukremin Kilic

Title: "Mysterious Fast Radio Bursts"

Abstract: Recently discovered Fast Radio Bursts are millisecond-long radio pulses coming half way across from the observed Universe. The peak luminosity, in radio, are billions of solar lumonicity (but just for a millisecond!). The *simplest* explanation involves a star of the order of mass of a Sun, compacted to 10 km, having quantum magnetic field of ~ 1010 Tesla, spinning at fraction of second, and having magnetopshere populated by relativistic beams of particles moving at Lorentz factor ~ 102-103. I will discuss astronomical and plasma physics challenges, and offer a few insights on the new, astrophyscailly-important plasma regime, that of an extremely magnetized relativistic plasma.

Title: "Using Photons to Understand and Change Defects in Semiconductors"

Abstract: The optical properties of semiconductors are inextricably linked to their electronic and vibrational properties. Electronic transitions from hydrogenic impurities and vibrational modes of mass defects lead to well-defined peaks in the infrared (IR) spectrum that provide information about the symmetry and chemical composition of the defects. Optical techniques such as photoluminescence (PL) provide researchers with a (mostly) nondestructive method for identifying defects. Light can also change defects, especially those that undergo large relaxation when their charge state changes. The DX center, for example, can absorb a photon and move to its shallow-donor site, leading to persistent photoconductivity (PPC) at low temperatures. In certain perovskite oxide semiconductors, substitutional hydrogen can be optically excited, causing the proton and electrons to leave. This leads to large room temperature PPC. Similar processes may cause photochromism, which is a change in sample color after exposure to light. We discovered a remarkable example of this effect in Cu-doped β-Ga2O3, an ultra-wide bandgap semiconductor.

Spring 2023

Host: Ian Sellers

Title: "Materials analysis and modifications using energetic ion beams"

Host: Xinyu Dai

Title: "Rotation, Magnetism, and Mass Loss of Sun-Like Stars"

Host: Joseph Tischler

Title: "Engineering Layered Materials"

Host: Xinyu Dai

Host: Nathan Kaib

Title: "Toward a More Equitable and Effective Physics Graduate Admissions Process"

Host: Brad Abbott

Title: "Exploring Physics Beyond the Standard Model with DUNE"

Host: Nathan Kaib

Title: "The early secular evolution of the outer solar system and the present state of the Nice Model"

Host: Howie Baer

Title: "Physics at the HEP energy frontier"

Host: Doerte Blume

Title: "A quantum generative adversarial network for mapping entanglement"

Fall 2022

Host: Thirumalai Venkatesan

Title: "Correlated Nanoelectronics and the Second Quantum Revolution"

Title: "Extended Extragalactic Journey with Active Galactic Nuclei, Galaxy Clusters, and Planet-Mass Objects"

Title: "Particles or Principles? The Hunt for New Physics Across Scales"

Title: "Revolution in Stellar Astrophysics and the Remaining Challenges"

Title: "Strange metal phase and quantum thermalization in nodal materials"

Host: Ian Sellers

Title: "Probing the structure, epitaxy and bonding at the single atom level in 2D materials and small molecules using Advanced Electron Microscopy"

Host: Robert Lewis-Swan

Title: "Exploring Long Range Dipolar Interactions: From collective dipolar spin dynamics and layer exchange to light-mediated interactions and Pauli-Blocking"

Host: Karen Leighly

Title: "(Extremely!) High Velocity Outflows in Quasars"

Host: Arne Schwettmann

Title: "Quenches and Disorder-free Localization in Interacting Trapped-Ion Spin Chains"