Events at Physics |
Events During the Week of February 5th through February 12th, 2023
Monday, February 6th, 2023
- Atomic Physics Seminar
- Beyond quantum circuits with trapped-ion qubits
- Time: 11:00 am
- Place: 5310 Chamberlin Hall
- Speaker: Or Katz, Duke University
- Abstract: Trapped ions are a leading quantum technology for quantum computation and simulation, with the capability to solve computationally hard problems and deepen our understanding of complex quantum systems. The quantum circuit model is the central paradigm for quantum computation, enabling the realization of various quantum algorithms by application of multiple one- and two-qubit entangling operations. However, the typical number of entangling operations required by this model increases exponentially with the number of qubits, making it difficult to apply to many problems.
In my presentation, I will discuss new methods for realizing quantum gates and simulations that go beyond the quantum circuit model. I will first describe a single-step protocol for generating native, N-body interactions between trapped-ion spins, using spin-dependent squeezing. Next, I will present a preparation of novel phases of matter using simultaneous and reconfigurable spin-spin interactions. Lastly, I will explore new avenues to harness the long-lived phonon modes in trapped-ion crystals for simulating complex bosonic and spin-boson models that are difficult to solve using classical methods. The presented techniques could push the performance of trapped-ion systems to solve problems that are currently beyond their reach.
- Plasma Physics (Physics/ECE/NE 922) Seminar
- The Eulerian space-time correlation of magnetohydrodynamic turbulence and the analysis of Parker Solar Probe measurements
- Time: 12:00 pm
- Place: 2241 Chamberlin Hall
- Speaker: Jean Carlos Perez, Florida Institute of Technology
- Abstract: Understanding the Eulerian space-time correlation of magnetohydrodynamic (MHD) turbulence, as well as its possible universal properties, is of critical importance in the analysis and interpretation of solar wind measurements when the Taylor hypothesis is not valid. This so-called frozen-in-flow hypothesis posits that the temporal variation of spacecraft signals is solely due to the spatial variation of a frozen structure passing by the observation point, in which case the turbulence dynamics can essentially be considered to be frozen in the plasma frame. The Parker Solar Probe (PSP) mission, launched in 2018, is presently probing the near-Sun solar wind with an orbit that will reach its point of closest approach next year at a heliospheric radius of approximately 0.045 au, which is seven times closer than any previous mission. During each close encounter with the Sun, the assumptions supporting TH are expected to break down. In this talk, I will discuss a recent semi-phenomenological model of the Eulerian two-time two-point (space-time) correlation for incompressible MHD turbulence and its impact on the interpretation of PSP data. Using this model we introduce a methodology that allows one to reconstruct the reduced energy spectrum of magnetic fluctuations vs spatial wavenumber from the frequency spectrum of fluctuations measured by PSP near the Alfven critical point, where TH is expected to break down.
- Host: Stanislav Boldyrev
Tuesday, February 7th, 2023
- R. G. Herb Condensed Matter Seminar
- Building Tools for the Quantum Many-Body Problem: The Case of Fractional Chern Insulators
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Daniel Parker , Harvard
- Abstract: The intermediate coupling regime of the quantum many-body problem --- where kinetic and potential energy compete on the same order --- is notoriously difficult. Analytical approaches there are generically uncontrolled, and numerical tools are often insufficient. However, experiments on the growing array of two-dimensional materials routinely probe this regime. To understand such experiments, a new intermediate coupling toolkit must be developed. This talk will focus on recent experiments in magic-angle graphene that detected fractional Chern insulators. Fractional Chern insulators (FCIs) realize the remarkable physics of the fractional quantum Hall effect in crystalline systems with Chern bands, casting off the typical requirements of Landau levels and strong magnetic fields. Understanding these intermediate-coupling experiments required an "all of the above" approach, combining close experimental collaborations with new theoretical and numerical tools. I will start by briefly overviewing the experimental phenomenology: in small magnetic fields, FCIs compete with charge-density waves due to the significant band dispersion. Next I will introduce ``vortexable bands", a class of beyond-Landau level systems with exact FCI ground states. Magic-angle graphene is vortexable in a limit, making the realistic system almost ideal for FCIs. Finally, I will use the new numerical technique of ``MPO compression" to compute the phase diagram of FCIs in magic-angle graphene, predicting where experiments should look to find FCIs in zero external magnetic field. Future work will study pairs of Chern bands related by time-reversal symmetry that, instead of FCIs, naturally host superconductors.
- Host: Victor Brar
Wednesday, February 8th, 2023
- Preliminary Exam
- Searches for transient astrophysical neutrino sources with IceCube
- Time: 10:00 am
- Place: 4274 Chamberlin
- Speaker: Jessie Thwaites, Physics Graduate Student
- Abstract: Multi-messenger astrophysics is a powerful tool for understanding the most energetic sources in the universe. Although IceCube has discovered a flux of extragalactic neutrinos, the sources of the vast majority of those neutrinos remain a mystery. We describe searches for neutrino emission from transient astrophysical source classes, both in archival searches and real-time analyses. In archival data, we use IceCube-DeepCore to search for GeV neutrinos from novae, and set the first upper limits on neutrinos from novae. We describe a planned search for neutrinos from fast radio bursts (FRBs) using the first catalog published by the CHIME/FRB Collaboration, which provides more than an order of magnitude more sources than previous IceCube FRB searches. We also describe real-time follow-up searches for neutrinos from astrophysical transients, including for the brightest gamma-ray burst ever recorded, GRB 221009A, for which we report a non-detection and set strong constraints on neutrino emission. We also describe planned follow-ups of gravitational wave events during LIGO-Virgo-KAGRA operating run 4, which is anticipated to start providing alerts as early as mid-February 2023.
- Host: Justin Vandenbroucke
- Physics ∩ ML Seminar
- Bayesian Renormalization: An explicit correspondence between statistical inference and exact renormalization
- Time: 11:00 am
- Place: Online Seminar: Please sign up for our mailing list at www.physicsmeetsml.org for zoom link
- Speaker: Marc Klinger, University of Illinois Urbana-Champaign
- Abstract: Renormalization is a ubiquitous tool in theoretical physics used to understand the role of scale in organizing natural phenomena. In this presentation we will report on a new information theoretic perspective for understanding the Exact Renormalization Group (ERG) through the intermediary of Bayesian Statistical Inference. This connection is facilitated by the Dynamical Bayesian Inference scheme, which encodes Bayesian inference in the form of a one parameter family of probability distributions solving an integro-differential equation derived from Bayes’ law. Utilizing the picture of an ERG flow as a functional diffusion process, we arrive at a dictionary outlining how renormalization can be understood as an inverse process relative to a Dynamical Bayesian inference scheme. A particularly salient feature of this correspondence is that it identifies the role of Fisher geometry in providing an emergent scale for “Bayesian Renormalization” that is related to the precision with which nearby points in model space can be differentiated. We comment on the usefulness of this identification in data science applications including possible implementations of “Bayesian Renormalization” as a tool for refining diffusion learning techniques.
- Host: Gary Shiu
- Atomic Physics Seminar
- Quantum many-body physics with ultracold molecules
- Time: 11:00 am
- Place: 5310 Chamberlin Hall
- Speaker: Zoe Yan , Princeton University
- Abstract: A central challenge of modern physics is understanding the behavior of strongly correlated matter. Current knowledge of such systems is limited on multiple fronts: experimentally, these materials are often difficult to fabricate in laboratory settings, and numerical simulations become intractable as the number of particles approaches meaningful values. In the spirit of Feynman, physicists can model diverse phenomena, from high-temperature superconductivity to quantum spin liquids, using analog quantum simulation. My research explores emergent quantum phenomena in pristine systems made of atoms, molecules, and electromagnetic fields. In particular, ultracold molecules are a promising platform due to their tunable long-range interactions and large set of internal states. However, this nascent platform requires new experimental techniques to create, control, and probe molecular systems.
I will report on efforts to create ultracold polar molecules, coherently manipulate their internal levels, and demonstrate second-scale coherence times in a molecular ensemble. To leverage the long-range, anisotropic dipolar interactions, we engineer dipolar collisions in a bulk ensemble using the technique of microwave dressing. Upon loading polar molecules into a 2D optical lattice, we study dynamics and thermalization in a variety of spin models relevant to quantum magnetism. Toward that end, we develop a novel readout modality – quantum gas microscopy – to perform site-resolved fluorescence imaging, enabling the measurement of quantum correlations and entanglement. The techniques presented here establish ultracold molecules as a compelling platform for quantum science and technology.
- Host: Thad Walker
- Department Meeting
- CLOSED Department Meeting
- Time: 12:15 pm
- Place: virtual - link to be sent later.
- Speaker: Mark Eriksson, UW-Madison
- Closed meeting to discuss personnel matters—pursuant to Section 19.85(1)(c) of the Wisconsin Open Meetings Law.
Closed to all but tenured faculty - Host: Mark Eriksson
- Theory Seminar (High Energy/Cosmology)
- New Physics with Gravitational Waves
- Time: 1:00 pm
- Place: 5280 Chamberlin
- Speaker: Jan Schuette-Engel, University of Illinois
- Abstract: The thermal plasma in the early universe produced a guaranteed stochastic gravitational wave (GW) background, which peaks today in the microwave regime and was dubbed the cosmic gravitational microwave background (CGMB). I show that the CGMB spectrum encodes fundamental information about particle physics and gravity at ultra high energies. In particular, one can determine from the CGMB spectrum the maximum temperature of the universe and the effective degrees of freedom at the maximum temperature. I point out that quantum gravity effects arise in the CGMB spectrum as corrections to the leading order result. At the end of the talk I discuss detection prospects of the CGMB.
- Host: George Wojcik
Thursday, February 9th, 2023
- R. G. Herb Condensed Matter Seminar
- Constructive approaches to frustrated magnetism: Moiré and Measurements
- Time: 10:00 am
- Place: 5310 Chamberlin Hall
- Speaker: Zhu-Xi Luo, Harvard University
- Abstract: Frustrated magnetism arises when spins interact through competing exchange interactions which cannot be simultaneously satisfied. When the frustrations are strong enough, exotic states can emerge such as long-range entangled spin liquids. Unfortunately, solid state materials are complicated and frustrations are hard to control: To this date, quantum spin liquids are still challenging to be realized in experiments. Naturally, researchers seek more manageable experimental systems, in the hope of engineering frustrated magnetism constructively. I will discuss my recent works in two types of such manageable systems: moire heterostructures in van der Waals materials where many tuning knobs are available; and monitored quantum circuits where designer gates and measurements are exploited as new sources of frustrations.
- Host: Victor Barr
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Hunting EeV Neutrinos with RNO-G and PUEO
- Time: 2:30 pm
- Place: Chamberlin 4274
- Speaker: Cosmin Deaconu, University of Chicago
- Abstract: The Radio Neutrino Observatory - Greenland (RNO-G) and the Payload for Ultrahigh Energy Observations (PUEO) are two experiments under construction seeking to detect for the first time the elusive ultrahigh-energy (>~ 100 PeV) neutrinos. Such neutrinos are expected to be produced from interactions of cosmic rays with photons and potentially in astrophysical sources, but detection is challenging due to the low flux. Both experiments operate by attempting to detect the impulsive Askaryan radio emission produced in showers induced by energetic neutrinos interacting in glacial ice. PUEO is a long-duration balloon payload, expected to fly over Antarctica in 2024, while RNO-G uses embedded antennas in Greenland and started deployment in 2021. In this talk, I will discuss the science goals, design considerations and implementation progress of both experiments.
- Host: Marjon Moulai
- Astronomy Colloquium
- Blue Stragglers, Blue Lurkers and Stars that Go Bump In the Night
- Time: 3:30 pm
- Place: 4421 Sterling Hall
- Speaker: Robert Mathieu, University of Wisconsin - Madison
- Abstract: A substantial fraction of evolved late-type stars in the Milky Way have
evolved along alternative stellar evolutionary paths in binary systems, both
in star clusters and in the field. As a case in point, in the 4-Gyr open
cluster M67, 25% of the evolved stars do not lie on the single-star
evolutionary isochrone. Thus, understanding these alternative stellar
evolutionary paths are essential to understanding stellar evolution, and to
correctly interpret ensemble studies of stars in the Milky Way.
Today, blue stragglers are seen as the most evident part of a much larger
population of evolved stars that do not fall on a classical single-star
evolutionary path. Indeed recently this population has suddenly grown
further to include a population of such stars lurking within main sequences.
All of these stars trace major alternative pathways of stellar evolution.
They are not anomalous.
Over the last decade observations have shown that most of these stars are
themselves binary stars. Relatedly, theory has argued that they likely form
from an array of processes within binary stars, including mass transfer,
mergers, collisions, and rapid rotation. I will tell of this discovery
journey through the landscape of rich open clusters. - Host: Ke Zhang
Friday, February 10th, 2023
- Physics Department Colloquium
- Ultracold Inferno” to Quantum Computing: Collisions Under Quantum Control
- Time: 3:30 pm
- Place: Chamberlin 2241
- Speaker: Micheline Soley , UW Madison - Department of Chemisty
- Abstract: Low-energy ultracold molecules offer an unprecedented opportunity to examine chemical reactions at the level of individual quantum states and to develop quantum computers based on ultracold molecular qubits. Theoretical developments are needed to help expedite these technologies, but are stymied by the fact that ultracold molecular processes are notoriously difficult to simulate. In this talk, I will present a method that addresses this problem based on the finding that, whereas low temperatures are typically associated with quantum mechanics, an approach based on classical and semiclassical methods can reduce anomalous reflection error in certain ultracold simulations from 100% to 0% at a single energy. This approach provides a tool for tackling the “ultracold inferno” problem of understanding how molecules are produced close to zero Kelvin. This semiclassical technique, combined with a theory from optics, provides an explanation of and the means to reveal long-sought-after PT-symmetry behavior in quantum mechanics. In addition, the talk will discuss quantum computing algorithms, both on quantum computers and classical computers using advanced data compression techniques.
- Host: Baha Balantekin, Bob Joynt
Saturday, February 11th, 2023
- Wonders of Physics
- The Wonders of Physics 40th annual show
- Time: 1:00 pm
- Place: 2103 Chamberlin
- Abstract: The Wonders of Physics annual show is a fast-paced, engaging, and educational physics program, filled with demonstrations that help people better understand the physics in the world around them, while having fun at the same time.
- Wonders of Physics
- The Wonders of Physics 40th annual show
- Time: 4:00 pm
- Place: 2103 Chamberlin
- Abstract: The Wonders of Physics annual show is a fast-paced, engaging, and educational physics program, filled with demonstrations that help people better understand the physics in the world around them, while having fun at the same time.
Sunday, February 12th, 2023
- Wonders of Physics
- The Wonders of Physics 40th annual show
- Time: 1:00 pm
- Place: 2103 Chamberlin
- Abstract: The Wonders of Physics annual show is a fast-paced, engaging, and educational physics program, filled with demonstrations that help people better understand the physics in the world around them, while having fun at the same time.
- Wonders of Physics
- The Wonders of Physics 40th annual show
- Time: 4:00 pm
- Place: 2103 Chamberlin
- Abstract: The Wonders of Physics annual show is a fast-paced, engaging, and educational physics program, filled with demonstrations that help people better understand the physics in the world around them, while having fun at the same time.