Colloquium Calendar

The essence of computation

Computation is strange and interesting. Despite much work in the mathematical foundations of computability theory, we do not yet have a complete understanding of the nature of computation. This is due, in part, with mistaking these mathematical foundations—a model of one type of computation—for a foundation of computation in general. I will argue why this is a mistake, and sketch a way that we might fix this mistake. On the account I sketch, we can make sense of computation in digital and analog systems, and in artificial and natural systems. Moreover, we can provide empirical criteria for when some physical system is a genuine computer, versus when it can be merely described in computational terms.

The Structure of the Nucleon

Nucleons (protons and neutrons) are the building blocks of atomic nuclei and are responsible for more than 99% of the visible matter in the universe. Despite decades of efforts in studying the structure of the proton, there are still interesting puzzles surrounding the proton such as its spin and the charge radius. The mass of the proton is another fascinating topic as most of the proton mass has little to do with the mass of its constituents. In this talk I will review some recent advances in the study of the nucleon structure, and then discuss future studies with an Electron-Ion Collider to be built at the Brookhaven National Laboratory in the coming decade.

THE DEMOGRAPHICS OF SMALL EXOPLANETS

The diversity of the exoplanet population is beyond our imagination. The more than 5000 known exoplanets vastly differ in mass, size, orbital period, dynamics, and host type. Demographic studies, however, aim to find patterns in the population that inform us about their origin, composition, and evolution. Among these features, perhaps the most surprising is the abundance of planets with no analog in the solar system, also known as sub-Neptunes. In this talk, I will review the state-of-the-art regarding the detection and characterization of such planets and what we know today about their enigmatic nature. A definitive answer, however, seems within reach during this decade thanks to the game-changing observations that will be provided by JWST, PLATO, and ARIEL.

Top-down Production of Macroscopic Monolayers For Study of Static and Dynamical Properties

Two dimensional (2D) materials and their artificial structures hold great promises for electronic, optoelectronic, and electrochemical applications. The best quality monolayers for exploring the exotic quantum properties so far are mostly produced by scotch tape exfoliation, which is stochastic and often yields microscopic sized monolayers. On the other hand, bottom-up growth techniques such as chemical vapor deposition often produces monolayers lower in quality. Beyond the Scotch tape exfoliation, we developed a few new scalable and controllable top-down processes to exfoliate a variety of van der Waals (vdW) single crystals into monolayers and monolayer nanoribbons with high yield, high quality, and macroscopic dimensions.  High-quality and large-area crystals will allow us to further assemble them into artificial heterostructures. The monolayers and other 2D artificial structures have been demonstrated to achieve enhanced nonlinear optical responses, and integrate into multiple pump probe techniques as electron diffractions to explore the key static and dynamic properties in these low dimensional systems. Obtaining high quality materials with enhanced yield will not only facilitate the basic research, but also take us one step closer to mass production and commercialization of the 2D devices in the future.

New Search Methods for DM Particles

Abstract: It is well known that a light, pseudo-scalar particle called the Axion can solve several fundamental physics problems.  Proposed to explain the lack of a neutron EDM, such a weakly interacting particle has the right characteristics to explain formation of galaxies, by providing the needed mass in the form of Cold Dark Matter.  There have been a number of completed and proposed experiments to detect axionic particles taking approaches as varied as condensed matter energy band gap to superconducting magnetic cavities.  This talk will review the theory behind axion particles, examples of early experimental searches and some new search techniques.  One question this talk will broach is whether or not observations of nuclear behavior, a place where axionic matter is theorized to play a role in neutron spin, can provide appropriate experimental conditions to be used in axion searches.  

Measuring intact protons at the LHC: From the odderon discovery to the search for axion-like particles

Abstract: In the first part of the talk, we will describe the odderon discovery by the TOTEM and D0 experiments. The analysis compares the p pbar elastic cross section as measured by the D0 Collaboration at Fermilab at a center-of-mass energy of 1.96 TeV to that in pp collisions as measured by the TOTEM Collaboration at CERN at 2.76, 7, 8, and 13 TeV. The two data sets disagree at the 3.4 sigma level and thus provide evidence for the odderon. Combining these results with previous TOTEM results leads to a combined significance larger than 5 sigma. 

In a second part of the talk, we will describe the search for axion-like particles with intact protons in the final state, leading to sensitivities to beyond standard model physics that improve by 2 to 3 orders of magnitude on the coupling compared to LHC standrad methods. 

We will finish by describing briefly the ultra fast silicon detectors for timing measurements as well as for medical and cosmic ray physics applications with KU medical and NASA.

Transitions without Symmetry: exploring exotic materials that challenge our conventions

Abstract: The collective behavior of electrons in solids is at the root of some of the most important questions in condensed matter physics, from solving the riddle of high temperature superconductivity to creating quantum technologies. Two concepts are critical foundations of our understanding of electrons in materials; the concept of the quasiparticle and the concept of broken symmetry phase transitions. In exotic metals, many of which are connected to unconventional superconductors, both these concepts break down. In this colloquium, I give a summary of the challenge that these systems present to the conventional picture of condensed phases of matter, some intriguing new developments in the field and possible ways forward.

High Resolution Storage Phosphor Dosimetry

Abstract: Proton beams are increasingly utilized for radiotherapy as they can confer unique dosimetric advantages due to their highly targeted dose deposition within a narrow Bragg peak. Electromagnetic interactions stemming from their charged nature result in the bulk of their radiation dose being deposited under a narrow area under their Bragg peaks which spares distal organs-at-risk. Other than its inherent physics, recent advances in medical cyclotron designs have also allowed for the creation of smaller proton beams are magnetically scanned across a tumor volume. While such beam delivery techniques are more challenging than their predecessors, this technology is rapidly becoming a mainstay within modern proton centers due to their ability to create highly conformal proton plans which greatly expands its clinical usefulness. However, the potential clinical benefit of proton therapy is heavily contingent on the spatial and dosimetric accuracies of these proton beams; any slight systematic variations in the pencil beams’ nominal position or dose can lead to significant differences in the clinical outcome especially due to the reduced robustness of proton treatments. These differences may be even further accentuated due to protons being more biologically damaging than photons by virtue of its higher linear-energy-transfer (LET) value. Despite this, there is not a convenient commercial solution to the current clinical need of a high-resolution absolute proton dosimeter. In this work, we studied the use of near water-equivalent storage phosphor dosimeter materials for high-resolution proton dose and LET simultaneous measurements. Storage phosphors are a class of dosimetry materials that function using the mechanism of photostimulated luminescence (PSL). Irradiation of these dosimeters will result in the production of electron-hole pairs that will be stored in metastable charge storage centers. The spatial distribution of these charge carriers will form a latent image that can be read out by optically stimulating the charge carriers to recombine and release PSL photons that are proportional in intensity to the locally deposited dose. The latent charges remaining after readout can be erased completely with a bright, broadband light which will render the material reusable. Their clinical use can also be potentially expanded in the near future for the purposes of proton FLASH dosimetry, high-resolution patient-specific conformal filter dosimetry, and spatial fractionated proton dosimetry.

High-Temperature Superconductors for Fusion Energy

Abstract: Decades of worldwide, government-sponsored research in fusion science have established the tokamak-based configuration as the leading approach to confining fusion-grade plasmas with strong magnetic fields. Yet in the past even state-of-the art superconducting magnet technology required tokamaks to be enormous to produce net fusion energy. High-temperature superconductors have recently reached industrial maturity. Commonwealth Fusion Systems is using these high-temperature superconductors to build smaller and lower-cost tokamak fusion systems. Following our successful demonstration of a large-bore, 20-Tesla, all-HTS magnet in September 2021, we have begun construction of an energy-breakeven fusion device called SPARC that will be commissioned in 2025. A fusion pilot plant called ARC will follow, with the aim of putting fusion power on the grid in the early 2030s. In this talk I will explain why high-field HTS magnets are a game changer for fusion energy, and I will review progress on the design and construction of fusion machines that will provide limitless, clean, fusion energy to combat climate change.