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Events on Thursday, December 8th, 2022

R. G. Herb Condensed Matter Seminar
Spin-phonon effects in nitrogen-vacancy centers
Time: 10:00 am - 6:00 pm
Place: 5310 Chamberlin
Speaker: Matt Cambria , UW-Madison
Abstract: Spin-phonon interactions provide solid-state qubits with both a unique obstacle to long coherence times, as well as a useful property to exploit for quantum sensing. In this talk, we discuss our recent efforts to understand spin-phonon interactions in the nitrogen-vacancy (NV) center in diamond. In particular, we present measurements of phonon-limited relaxation rates within the NV center's electronic ground state spin triplet manifold. Informed by ab initio work, we determine that NV spin-phonon relaxation is dominated by interactions with phonons whose energies are centered at two characteristic frequencies. We adapt this observation into a semi-empirical model that provides excellent agreement with the experimental data. We discuss how a similar model can describe the NV center's zero field splitting, a quantity fundamental to NV-based thermometry schemes. Finally, we identify an NV qubit subspace that is immune to spin-phonon dephasing, and we predict that such a qubit could exhibit record NV electronic spin coherence times.
Host: Alex Levchenko
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Preliminary Exam
Constraining the Diffuse Flux of Ultra-High Energy Neutrinos with the Askaryan Radio Array’s Largest Analysis Ever
Time: 2:00 pm
Speaker: Abigail Bishop, Physics Graduate Student
Abstract: In the race to discover the first ultra-high energy neutrinos and zoom in on the ultra-high energy neutrino flux, the Askaryan Radio Array (ARA) is a frontrunner. Similar to the world renowned IceCube Neutrino Observatory, ARA deploys radio antennas in glaciers and searches for the ultra-high energy Askaryan emission radiating from cosmic neutrino interactions in the ice. Even though ARA can see neutrino interactions in volumes far greater than IceCube, the tremendously low flux of ultra-high energy neutrinos makes them even rarer to observe than the mid-high energy neutrinos IceCube detects. ARA has been operating for a decade and is composed of 5 separate stations, but historically each analysis has analyzed only one or two stations over the course of a few years. Presently, our collaboration is building the framework for a full 5 Station Analysis over every year of ARA operation and I am on the ground level of this effort. I propose a thesis project contributing to this leading edge, comprehensive neutrino search, performing an estimate of the diffuse neutrino flux considering every byte of ARA data, with personal emphasis on searching for unique signal topologies that can allow us to confidently identify neutrino candidates in, what used to be classified, as noise.
Host: Albrecht Karle
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Astronomy Colloquium
Linking Planet Formation to Exoplanet Composition
Time: 3:30 pm - 4:30 pm
Place: 4421 Sterling Hall
Speaker: Prof. Edwin(Ted) Bergin, University of Michigan
Abstract: For the past decade we have begun to explore the origin of planetary compositions which are set in the natal protoplanetary disk. In this talk I will explore these links via two lenses that of giant planets formed far from their star and in smaller Earth-sized planets in the inner regions of planetary systems. For giant planets the primary link has been through the elemental C/O ratio. This is theorized to vary with position in the planet-forming disk as the main carriers of C and O (H2O, CO, and CO2) have spatially separated gas-ice sublimation fronts. I will outline the methodology via which the C/O ratio is traced within disk systems using data from the Atacama Large Millimeter Array (ALMA). I will then summarize the state of knowledge through a comparison of ALMA measurements of the C/O ratio to those measured with high accuracy in distant exoplanets and discuss what this means for the origins of these planetary systems. For the second part of my talk, I will explore the disposition of elemental carbon via new model of planet formation in the inner parts of the disk. This model relates the initial mantle composition of the planet to its formation zone around its star, factoring in the relative contributions of refractories (metals and silicates) and volatile components (solid state organics, water vapor/ice, and hydrogen-dominated nebular gas). We predict that a population of super-Earth’s and mini-Neptune’s will form in particular locations in their protoplanetary disks such that they receive significant inventories of organics, but very low amounts of water. As a result of geochemical equilibrium, the mantle of such a planet would be rich in reduced carbon but have relatively low oxygen (water) content. Outgassing would naturally yield the ingredients for haze production, which is widely observed in these systems. Although this type of planet has no solar system counterpart, it should be common in the galaxy.
Host: Ke Zhang
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Treasure Maps for Detections of Extreme Energy Cosmic Rays
Time: 4:00 pm - 5:00 pm
Place: CH 4274
Speaker: Anatoli Fedynitch, Academia Sinica, Taiwan
Abstract: The origin of Ultra High Energy Cosmic Rays is a 60-year old mystery. We show that with more events at the highest energies (above 150~EeV) it may be possible to limit the character of the sources and learn about the intervening magnetic fields. Individual sources become more prominent, relative to the background, as the horizon diminishes. An event-by-event, composition-dependent observatory would allow a ``tomography'' of the sources as different mass and energy groups probe different GZK horizons. A major goal here is to provide a methodology to distinguish between steady and transient or highly variable sources. Using recent Galactic magnetic field models, we calculate ``treasure'' sky maps to identify the most promising directions for detecting Extreme Energy Cosmic Rays (EECR) doublets, events that are close in arrival time and direction. On this basis, we predict the incidence of doublets as a function of the nature of the source host galaxy. Based on the asymmetry in the distribution of time delays, we show that observation of doublets might distinguish source models. In particular the Telescope Array hotspot could exhibit temporal variability as it is in a ``magnetic window'' of small time delays. These considerations could improve the use of data with existing facilities and the planning of future ones such as Global Cosmic Ray Observatory - GCOS.
Host: Lu Lu
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