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Colloquia

We will be hosting both in-person and virtual seminars.

Due to the COVID-19 virus,  masks are mandated for all seminars.

Zoom Links will be provided on the calendar and through email.

Physics Department Colloquia

Fall 2023

Organizer: Vito Scarola

These meetings occur on Fridays from 2:30pm to 3:30pm in Hahn Hall 130 or/both
Virtual Meetings (unless otherwise indicated)

September 2023
September 1

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Dr. Travis Fisher (Space Telescope Science Institute)

"Let's Talk About Jets: Sources of Radio Emission in NGC 1068 and Friends"

We present multi-wavelength,spatially-resolved imaging and spectroscopy in effort to study thecharacteristics of the extranuclear radio emission in nearby radio-quiet AGN.From our recent studies, we have noted that radio structures in previousanalyses of these objects align and intertwine with their optical Narrow-LineRegions (NLRs), which represent the intersection between AGN ionization andhost galaxy disk material. We hypothesize that radiatively-driven winds,launched from small radii, impact dense gas lanes at larger distances andproduce shocks, with relativistic particles accelerated in the shocks in turnproducing localized synchrotron radio emission similar to processes insupernova remnants. In this scenario, the observed radio emissionis then a byproduct that occurs only at locations where winds are producingshocks in the radio-quiet AGN host galaxy. As this hypothesis lies in tensionwith the standard paradigm of radio structures in AGN, we present furthertesting on the radio structures observed in several AGN to provide evidence forthis scenario on how active black holes produce feedback and interact with theinterstellar medium in their host galaxies.

Host:

September 8

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Nahum Arav (Physics, Virginia Tech)

"The Contribution of Quasar Absorption Outflows to AGN Feedback"

Determining the distance of quasar absorption outflows from the central source and their kinetic luminosity are crucial for understanding their contribution to AGN feedback. Here we summarize the results for a sample of nine luminous quasars that were observed with the Hubble Space Telescope. We find that the outflows in more than half of the objects are powerful enough to be the main agents for AGN feedback. The sample is representative of the quasar absorption outflow population as a whole and is unbiased towards specific distance ranges or kinetic luminosity value. Therefore, the analysis results can be extended to the majority of such objects, including broad absorption line quasars (BALQSO)..

Host: Prof. Vito Scarola

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September 29

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Kevin Pitts (Physics, Virginia Tech)

"Measurement of the Anomalous Magnetic Moment of the Muon to 0.20 PPM"

Previous measurements of the anomalous magnetic moment of the muon have shown a sizeable discrepancy with standard model calculations. We present a new measurement from the Fermilab Muon g-2 experiment with twice the precision of our prior result.

Host: Prof. Mark Pitt

October 2023
October 7

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Fall Break No Colloquium

Host:

October 13

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Walfgang Losert (University of Maryland)

"Sensing Physical Signals with Mechano-chemical Waves"

How do living systems sense the physical properties of their surroundings? Here we consider the role of active elements in the cell, and describe how they can act as sensors of the physical microenvironment. We will focus on an active system that yields micron scale dynamics: Specifically, we study the assembly and disassembly of the cytoskeleton, which creates micron sale waves and oscillations that are critical to cell migration and other important cell behaviors. We demonstrate that cytoskeletal waves are directly involved in sensing both the microscopic texture of the surrounding and local DC electric fields. Notably, the symmetry of active waves can be broken by asymmetries of the environment, giving cells a sense of direction with a Brownian Ratchet type mechanism. In turn, these waves and oscillations drive signaling pathways, allowing cells to adapt their biological state to their physical environment.

Host: Prof. Camillo Mariani

October 20

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Sowjanya Gollapinni (Los alamos National Laboratroy

Host:

October 27

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

No Colloquium

Host:

November 2023
November 3

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Andrea Pocar (University of Massachusetts)

TBD"

.

Host:

November 10

Friday 2:30pm
Virtual Meeting Only
(Zoom Link)
(poster)

No Colloquium

Host:

November 17

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Host:

November 24

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Thanksgiving Break - No Colloquium

Host:

December 2023
December 1

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

""

Host:

Physics Department Colloquia

Spring 2023

Organizer: Vito Scarola

These meetings occur on Fridays from 2:30pm to 3:30pm
Virtual Zoom Seminars (unless otherwise indicated)

January 2022
January 20

Friday 2:30pm
Virtual Zoom & HHN 130

(poster)

Special Colloquium

Dr. Jahan Claes

"Tailoring quantum Error Correction for Structured Noise"

Large-scale quantum computers will require error correction in order to reliably perform computations. However, the hardware overhead for error correction remains dauntingly large, with each logical qubit potentially requiring thousands of physical qubits for reliable operation. One promising approach to reducing the overheads of error correction is to tailor quantum error correcting codes to the dominant noise in the qubit hardware. In this talk, I’ll present recent work on tailoring measurement-based quantum computing to biased noise. In the first part of the talk, I’ll explain the basics of measurement-based error correction and cluster states, and show how a cluster state derived from the XZZX surface code, the so-called XZZX cluster state, can effectively correct biased noise. In the second part of my talk, I’ll present two applications of the XZZX cluster state for increasing thresholds in both linear optical qubits and Rydberg atoms. These works demonstrate that carefully considering the dominant hardware noise when designing error correction protocols can drastically increase their effectiveness.

Host: Prof. Mark Pitt

January 27

Monday 2:30pm
304 Robeson Hall
Zoom Link
(poster)

Special Colloquium

Dr. Mouzhe Xie
(University of Chicago)

"Diamond-Based Quantum Sensor For Molecular Biophysics"

Quantum sensing technologies enable some of the most precise measurements that human beings have ever achieved. In recent years, optically addressable nitrogen-vacancy (NV) color center hosted by diamond crystal has been used as a quantum bit(qubit), which has exquisitely sensitive response to local magnetic field fluctuations. This diamond-based solid-state quantum sensor is therefore capable to perform micro-/nano-scale NMR experiments, displaying enormous potential to study biological systems on extremely small sample volume – even down to single-molecule regime. In this seminar, I will discuss some of the comprehensive efforts to develop NV-based quantum sensing platforms for a wide range of applications in biology and chemistry. I will start with a general introduction to quantum sensing and diamond material engineering, as well as how nanoscale NMR is connected to conventional NMR spectroscopy. I will then introduce a biocompatible surface functionalization architecture for interfacing a diamond quantum sensor with individual intact biomolecules under physiological conditions. A sensing modality based on diamond membrane integrated with flow channel device will also be discussed, which is a promising platform for a variety of experiments at molecular, cellular, and even living organism levels. Finally,I will conclude by providing an outlook on how NV-based quantum sensing platforms, combined with other advanced spectroscopy and microscopy methods, can be utilized to address important biophysical and bioanalytical questions with unprecedented sensitivity and spatial resolution, which will enhance our understanding of molecular interactions and cellular processes and ultimately improve human health.

Host: Prof. Mark Pitt

February 2023
February 3

Friday 2:30pm
130 Hahn Hall North
Zoom Link
(poster)

Special Colloquium

Dr. Sithara Wijeratne
(Harvard Medical School & Massachusetts General Hospital)

"Self-Organization and dynamics of Cellular Highways"

Analogous to the role of highways in our macroscopic world, the cytoskeleton organizes the cellular cytoplasm. Micron-sized cytoskeletal polymers, such as microtubules, link distant cellular sites. Nanometer-sized motor proteins walk on complex multi-microtubule highway systems to drive intracellular transport and also remodel, I will present two different aspects of microtubule organization in my seminar. First, I present an unexpected discovery that nanometer-sized proteins separated by several microns on microtubules can sense and respond to each other. This challenges the long-held view of microtubules as a passive platform and reveals how the microtubule is like a wooden bridge rather than a concrete highway. Second, I present the development of an Atomic Force Microscopy assay that enables us to directly visualize the dynamic features of individual microtubules within complex microtubule arrays. This imaging modality bridges the resolution gap between light and electron microscopy to reveal new insights by which complex microtubule arrays can be remodeled by associated proteins.

Host: Prof. Mark Pitt

February 10

Monday, 2:30pm
304 Robeson Hall
Zoom Link
(poster)

Special Colloquium

Dr. Bo Zhang
(Northwestern University)

"Manipulation of Collective Behaviors in Active Matter"

Active matter is a new class of intrinsically non-equilibrium soft condensed matter systems whose components can transduce energy from the environment into mechanical motion at its single unit level. The remarkable feature of active matter systems is their natural ability to collectively change structures and environmentally adapt in response to external stimuli on a much larger scale than their unit sizes. The collective behaviors of active matter are widely observed, such as the bird flocking and active turbulence of bacteria. Once controlled on-demand, such abilities will open a door to many influential applications such as targeted drug delivery and microsurgery. To achieve these, however, the motion has first to be well manipulated based on the mechanisms. In this colloquium, I am going to present my recent work on reconfigurable collective behaviors in active matter, focusing on developing a set of principles that facilitate the manipulation of emergent active states. In the first part, I will describe the unexpected reversal of a vortex of active colloidal particles induced by the temporal modulation of activity. In the second part, I will introduce shape-anisotropy into the system to realize chiral motions to form emergent patterns such as multiple vortices and rotating flocks. My work provides new fundamental insights into mechanisms of spontaneous formation of collective states in active matter and offers new prospects for the design pathways of active synthetic materials and microrobots.

Host: Prof. Mark Pitt

February 17

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Special Colloquium

Dr. Gregory Bentsen
(Brandeis University)

"Chaos, Scrambling, and Entanglement-Expanding the Frontiers of Many-Body Hilbert Space on Near-Term quantum Devices"

Many-body entanglement plays a vital role in the transformative information processing capabilities expected to materialize as quantum devices mature over the coming decades. Absent fault-tolerant error correction, however, noisy intermediate-scale quantum (NISQ) technologies of the near future must necessarily contend with noise and dissipation threatening to damage the delicate quantum information being processed on the device. The timescales of these noisy processes, in conjunction with Lieb-Robinson bounds determined by the physical geometry of the device, impose strict limits on the maximum number of qubits that can effectively participate in a given process before the system succumbs to dissipation. Here I will frame these issues in terms of a simple question: how quickly can a given quantum system access the many-body Hilbert space before dissipation corrupts the quantum state, and what can be done with such a system before the quantum state becomes unviable? Recent advances in our understanding of quantum information dynamics have emphasized the crucial role that quantum chaos, nonlocal interactions, and fast scrambling play in optimally exploring many-body Hilbert space. I will present experimental results demonstrating how light-mediated interactions in cavity QED systems can be harnessed to engineer effectively non-local interactions that enable access to the fast scrambling regime. Additionally, I will show how modern theoretical tools such as Brownian circuit models and stabilizer simulations can be applied to provide valuable insights and quantitative benchmarks for ongoing quantum simulation platforms as we work to expand the many-body frontier.

Host: Prof. Mark Pitt

February 24

Monday, 2:30pm
304 Robeson Hall
Zoom Link

(poster)

Special Colloquium

Dr.Arpit Dua
(California Institute of Technology)

"The Interplay of Quantum Error Correction with Physics and Geometry "

It has been roughly a century since the quantum revolution which led to the establishment of quantum mechanics as a fundamental theory of physics. Today we are in the age of quantum information science which is at the intersection of physics, computer science and mathematics. One big question in quantum information science is how to build a fault-tolerant quantum computer. Since qubits are susceptible to noise from the environment, quantum error correction is essential for building such a computer. In this colloquium, I will show how quantum error correction is a highly interdisciplinary topic having an interplay with physics and geometry. I will demonstrate the interplay of error correction with ideas of topological order, statistical mechanics and geometry using two works as examples. One is about random Clifford-rotated two-dimensional surface codes which outperform the best known-translation invariant surface codes in terms of threshold error rates and subthreshold logical error rates for biased Pauli noise. The second is about universal quantum computation with a two-dimensional code which is obtained by punching a macroscopic hole in the three dimensional surface code. Such a code provides a fault-tolerant implementation of a logical non-Clifford gate. I will summarize by mentioning problems in which error correction has a close interplay with developments in quantum dynamics and quantum many-body physics.

Host: Prof. Mark Pitt

March 2023
March 3

Friday 2:30pm
130 Hahn Hall North Zoom Link
(poster)

No Colloquium

Host:

March 10

Tuesday 4:00pm
Zoom Link
(poster)

Spring Break -No Colloquium


Host:

March 17

Friday 2:30pm
Zoom Link

(poster)

APS March Meeting Week -No Colloquium

Host:

March 24

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Dr. Minerba Betancourt
(Fermilab)

“From Idea to Discovery to Precision Measurements”

The discovery of neutrino oscillations opened new windows for the study of neutrino physics. In this talk, I will give an overview of the neutrino physics program at Fermilab and the remaining questions for the neutrino physics. I will highlight status of Short-Baseline (SBN) program at Fermilab. The SBN program consists of liquid argon time-projection chamber detectors located along the Booster and NuMI Neutrino Beams at Fermilab National Accelerator Laboratory. Its main goals include searches of light sterile neutrinos with unprecedented sensitivity in eV^2 mass range, a rich program of neutrino interaction measurements and novel searches for physics beyond the Standard Model.

Host: Mark Pitt

March 31

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Dr. Ori Fox
(Space Telescope Science Institute, NASA)

“The Dream Machine: First Light with the James Webb Space Telescope”

Launched on December 25, 2021, the James Webb Space Telescope is NASA’s newest flagship observatory. With a 6.5-meter primary mirror and wave length coverage from 0.6-25 micron, the Webb is already producing unprecedented images and fascinating results. This talk will provide a behind-the-scene look at Webb’s highlights over the past year, including launch, commissioning, first light images, and the latest science discoveries. Particular emphasis will be placed on transient astronomy with Webb, including my program to study dust production by supernovae using the Webb’s unprecedented infrared sensitivity. We will take a look at the preliminary results from the program’s first observations of two core-collapse supernovae and will discuss their implication on the origin of dust in the Universe. Finally, we will take a look ahead to what exciting transient discoveries may be on the horizon.

Host: Chris Ashall

April 2023
April 7

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Prof. Paola Rodriguez Hidalgo
(University of Washington-Bothell)

"High Velocity Outflows in Quasars and the Study of Galaxies Far, Far Away"

Quasars are among the most luminous objects in the universe. These very energetic regions lie at the center of massive galaxies and are powered by a supermassive black hole. While it has been found that there is a correlation between the mass of these supermassive black holes and the mass of the surrounding galaxies, the co-evolution of galaxies and quasars is barely understood. Outflows launched from the vicinity of supermassive black holes are a key piece in this puzzle, potentially linking the small and the large-scale phenomena. We have discovered that some of this gas is outflowing at very high speeds (speeds higher than 10% the speed of light, 0.1c). I will present a survey of these extremely high velocity outflows observed as broad absorption lines in Sloan Digital Sky Survey Data. This realm of the parameter space of quasar outflow's velocity has not been included in previous surveys of quasar spectra, and might pose the biggest constraints for theoretical models. Moreover, the kinetic luminosity of outflows at ~0.2c can reach two orders of magnitude larger than those speeding at high velocities (~10,000 km/s). Studying extremely high velocity outflows can help us understand the interaction between the central supermassive black hole and the host galaxy, so I will discuss the characteristics and properties of the found sample, as well as the current and future studies our research group is carrying out and planning out.

Host: Camillo Mariani

April 14

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Prof. Kenneth Schweizer
(University of Illinois)

"Ultra-Slow Activated Dynamics and the Glass Transition in Bulk Liquids and Under Broken Symmetry Conditions"

Understanding in a unified manner the universal and rich nonuniversal aspects of how and why liquids exhibit spectacular slowing down upon cooling of mass transport, relaxation, and flow over 14 or more orders of magnitude remains a grand challenge in condensed matter physics, materials science, and beyond. After providing an introductory overview of the basic experimental observations and classic phenomenological ideas, I will describe our efforts over the last decade to construct a predictive microscopic statistical mechanical theory that has been widely applied to colloidal, molecular, polymeric, and inorganic glass-formers. The core idea is to relate forces, structure, and thermodynamic state in a particle-level stochastic trajectory framework that quantifies transient localization and the effective barrier to thermally activated relaxation within a novel “dynamic free energy” framework. Moreover, we argue that in deeply supercooled liquids the relaxation process is of a spatially local-nonlocal nature, where localized large amplitude hopping events are strongly coupled with the long range collective elastic response of the medium far from the activated event. New predictions for how glassy relaxation in real materials depends on a density fluctuation based thermodynamic property, metrics of short range packing order, the short time localization length scale, and emergent dynamic shear elasticity have been made and extensively tested against experiment. A key conceptual conclusion is that thermodynamics is relevant only in a non-causal sense via its fundamental correlation with packing structure in equilibrium statistical mechanics. The theoretical approach has been generalized to the broken symmetry situation of cold liquids near surfaces and under geometric confinement. Large spatial gradients of the activated relaxation time are predicted of an unusual double exponential form that can extend 10-20 nanometers from the surface, which then cross over on larger length scales to a power law tail that directly reveals the importance of collective elasticity. Quantitative comparisons with simulations and experiments support these predictions. The talk will conclude with a broader outlook concerning how glass physics is relevant to a host of soft matter and materials science problems such as molecular diffusion in crosslinked networks, ion conduction in amorphous polymers, the mechanics of hybrid nanocomposites, and the dynamics of topologically crumpled synthetic and biological macromolecules

Host: Shengfeng Cheng

April 21

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Dr. Gerard Kriss
(Space Telescope Science Institute, NASA)

'Ionized Outflows from Active Galactic Nuclei: A Multiwavelength View'

The super-massive black holes at the centers of most galaxies achieve their greatest brilliance when accreting matter into their gravitational potentials. In active phases the resulting radiation can outshine the whole galaxy. A puzzle of galactic evolution, however, is that the mass of the central black hole is tightly related to the mass of the surrounding host. The popular solution for this conundrum for the past decades has been feedback suppressing star formation and expelling gas from the galaxy, fueled by winds arising from the accretion disk around the black hole. I will review evidence for such feedback mechanisms based on X-ray, ultraviolet, optical, and infrared observations of the outflowing winds using space-based observatories, culminating in some recent highlights from the new Webb space telescope.

Host: Nahum Arav

April 28

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Prof. Tatsu Takeuchi
(Virginia Tech)

'Reading the Principia for the First Time: F=ma is NOT the 2nd Law! and other Surprises"

I will argue that the usual way Newton's Laws are described in textbooks is quite misleading if not outright wrong. The introduction of "force" as a "push" or a "pull" is particularly problematic. To understand the true meaning of "force" and Newton's Laws, we need to go to the source, namely the Principia. What it says is quite surprising: we find that F=ma is NOT the 2nd Law, and that "reaction" in the 3rd law is NOT reaction (in the usual sense of the word). I will explain what Newton really meant by what he said in the Principia, and how his original formulation of his three laws makes much more sense, and is consequently much easier, than what the textbooks say.


Host: Vito Scarola

May 2023

May 5
Friday 2:30pm
Zoom Link
(poster)

No Colloquium

Host:

Physics Department Colloquia

Fall 2022

Organizer: Vito Scarola

These meetings occur on Fridays from 2:30pm to 3:30pm in Hahn Hall 130 or/both
Virtual Meetings (unless otherwise indicated)

September 2022
September 9

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Satoru Emori (Virginia Tech)

"A Secret of Pumping Iron: Revealing a Counterintuitive Mechanism of Magnetic Damping"

In any magnetic material, rotating the magnetization involves “damping,” somewhat akin to friction that dampens mechanical oscillations. Minimizing damping is crucial for energy-efficient nano-magnetic memories and signal generators. However, the mechanisms of damping in real materials – even in seemingly simple ones – have yet to be understood. In this talk, I will present a counterintuitive experimental insight into damping in simple model systems: crystalline thin films of iron. It turns out that the key damping mechanism arises from “procrastinating” electrons..

Host: Mark Pitt

September 30

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Dr. Mark Stevens (Sandia National Labs)

"TStructure of Flexible, Strongly Charged Polyelectrolytes"

Flexible, strongly charged polyelectrolytes such as single stranded RNA and sulfonated polystyrene present major challenges to experiment, theory and simulation. The combination of electrostatic interactions with entropy yields a complex set of interactions that is difficult to decipher. Our recent simulations provide new data on the structure of strongly charged polyelectrolytes. This structure will be discussed in the context of calculations of the overlap concentration c*, which is a fundamental quantity that is a prerequisite for many studies as c* separates the dilute and semi-dilute concentration regimes. We have calculated c* using molecular dynamics simulations of salt-free systems for using coarse-grained bead-spring models and atomistic models for sodium polystyrene sulfonate in water. We find an unexpected concentration dependence and that the scaling regime occurs at very long chain lengths.

Host: Prof. Shengfeng Cheng

October 2022
October 7

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Fall Break No Colloquium

Host:

October 14

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Dario Arena (University of South Florida)

Photon-(n/ Photon-Out Studies of Spin Dynamics and Orbital Populations in Ferri-and Ferromagnetic Thin Films"

We present results from a selection of experiments, primarily on ferrimagnetic (FiM) systems, which examine (1) spin dynamics across a wide frequency range, and (2) orbital populations and ground state spin distributions. Ferrimagnets (FiM) exhibit an intriguing magnetic order in between ferromagnets (FM) and anti-ferromagnets (AF). Common FM materials are characterized by a single exchange interaction (J) favoring parallel alignment of spins on adjacent lattice sites, while in AF materials the single exchange energy favors anti-parallel alignment, resulting in zero net moment for AF systems. Ferrimagnets are characterized by at least three exchange interactions between magnetic sublattices A and B (intra-lattice J AA and J BB favoring FM alignment and inter-lattice J AB with AF alignment between the sublattices).Ferrimagnets therefore exhibit a rich array of physical phenomena including's pin frustration, topological spin textures, and an intriguing phenomenon termed magnetic compensation where the sublattice magnetizations cancel out. We present optical studies of spin dynamics in FiM systems using complementary ultrafast, time-resolved optical probes: magneto-optical Kerr effect (tr-MOKE)using visible light and extreme UV probes generated by high harmonic generation(HHG). tr-MOKE is sensitive to the spin distribution at the Fermi level, which produces sensitivity to magnetic compensation in FiM films, while HHG permits access to shallow core-level excitations, enabling element-specific studies of spin dynamics at ultrafast timescales. We will discuss tr-MOKE studies o famor phous (FeCo) (1-x) Gd x metallic films through the region of magnetic compensation [1], tr-MOKE examinations of “artificial” ferrimagnets comprised of exchange-coupled magnetic mutli-layers [2], and also tr-HHG studies of NiFe 2 O4 which highlight the effects of coherent strain on the spin dynamics of the Niand Fe moments in the insulating oxide [1,3]. Additional topics on spin mixing in ferromagnets [4] may also be presented.

Host: Prof. Camillo Mariani

October 21

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Dr John Katsaras (Oak Ridge National Lab)

"Molecular Structures of Biological Membranes"

Biological cells are bounded by plasma membranes (PMs), supramolecular assemblies of lipids and proteins which separate a cell's interior from its external environment. Although the existence of cells has been known since the mid-19th century, it was not until the early part of the 20th century that the underlying structure of the PM began to emerge. However, it took another 50 years for Singer and Nicolson to propose the now well-known “Fluid Mosaic” model of the PM. I will describe neutron and x-ray scattering studies that have addressed the existence of lipid domains in membranes and conclude with the future use of lipid bilayers as platforms for understanding memory in the brain and for instructing the development of the next-generation of neuromorphic computers.

Host: Rana Ashkar

October 28

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Alan Calder (Stony Brook University)

"Cosmic Chandlery with Thermonuclear Supernovae"

Thermonuclear (Type Ia) supernovae are bright stellar explosions distinguished by light curves that can be calibrated to allow for their use as "standard candles" for measuring cosmological distances. Many fundamental uncertainties remain, however, and contemporary research investigates different proposed settings for these events and within a setting, systematic effects on the brightness and thus the intrinsic scatter. I will give an overview of thermonuclear supernovae, the physics therein, and our approach to modeling these events. I will also present preliminary results from our investigation into Type Iax supernovae, one class of dim events, and compare our results to observations.

Host: Chris Ashall

November 2022
November 11

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Omar Benhar (Sapienza University of Rome)

"Constraining Nuclear dynamics with Multimessage Astrophysical Data"

Over the past decade, the availability of astrophysical data collected by electromagnetic observatories and gravitational-wave (GW) interferometers, supplemented by the information obtained from Earth-based laboratory experiments, has opened a new era for the investigation of neutron star structure and dynamics. Besides being a valuable source of information on the Equation of State (EOS) of matter in the star interior, the new data provide an unprecedented opportunity to constrain the underlying models of nuclear dynamics at supranuclear density. The Bayesian approach has been recently employed to explore the possibility to constrain repulsive three-nucleon (NNN) forces—which are known to play the leading role in determining the stiffness of the EOS at high density—using both available and mock data. The results of these studies suggest that a single neutron star merger event observed by a third-generation GW interferometer, such as the Einstein Telescope or Cosmic Explorer, may allow to pin down the strength of the repulsive NNN potential with remarkable accuracy.

Host: Camillo Mariani

November 18

Friday 2:30pm
Virtual Meeting Only
(Zoom Link)
(poster)

Prof. Sophia Economou (Virginia Tech)

"quantum Entanglement: from foundations to technologies"

This year’s Physics Nobel Prize was awarded “for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science”. In this talk, I will discuss quantum entanglement and Bell’s inequalities. I will survey the key experiments that have been conducted over the decades to confirm the violation of these inequalities and describe the implications for the foundations of quantum mechanics. I will also explain how the same physics can lead to new ways of understanding and processing information and resulting novel technologies that are not possible without quantum entanglement.

Host: Vito Scarola

November 25

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Thanksgiving Break - No Colloquium

Host:

December 2022
December 2

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Liam McAllister (Cornell University)

"String Theory, The Cosmological Constant, and The Quantization of Parameters"

I will argue that the fundamental parameters in Nature are integers. In string theory these integers record the topology of six additional spatial dimensions. A task for theorists is to understand what values these numbers can take, and how experimental observables can be expressed in terms of them. One key observable is the dark energy density, which is 123 orders of magnitude smaller than the naive prediction from theory: this discrepancy is the famous cosmological constant problem. We have learned how to compute the fundamental integers in a vast class of geometries and have used this knowledge to construct solutions of string theory in which the dark energy density has an allowably small magnitude. But it has the wrong sign! I will explain why our result constitutes progress on a toy model of the cosmological constant problem.

Host: Sophia Economou

Physics Department Colloquia

Spring 2022

Organizer: Vito Scarola

These meetings occur on Fridays from 2:30pm to 3:30pm
Virtual Zoom Seminars (unless otherwise indicated)

January 2022
January 21

Friday 2:30pm
Virtual Zoom & HHN 130

(poster)

Special Colloquium

Dr. John Forbes
(Flatiron Institute)

"Towards a Predictive Theory of Galaxy Formation: Lessons From Turbulence in Disk Galaxies"

Galaxy formation is currently faced with immense datasets, both observational and simulated, with much more on the way. As the simulations continue to improve, I argue it is time to start thinking about how to use these realistic-looking galaxies to develop a predictive theory of galaxy formation. A new generation of semi-analytic models and statistical techniques are needed to simultaneously address the strong degeneracy that persist in the problem of galaxy evolution, and to coherently comprehend the vast quantities of extant and forthcoming data. I will focus on a particular set of puzzles around the turbulent driving in galactic disks - is stellar feedback, local gravitational instabilities, the direct impact of cosmological accretion, or something else responsible?

Host: Prof. Mark Pitt

January 24

Monday 2:30pm
304 Robeson Hall
Zoom Link
(poster)

Special Colloquium

Dr. DJ Pasham
(MIT)

"Multi-wave length studies of extra-galactic nuclear transients"

Extreme Mass Ratio Inspirals (EMRIs), containing a massive black hole and a stellar object (stellar-mass black hole, neutron star,white dwarf, or a star core), are expected to be one of the primary sources of gravitational waves with future space gravitational wave detectors. The identification of electromagnetic counterparts of these gravitational wave emitters would transform our understanding of supermassive black hole growth, probe dark energy and put fundamental constraints on gravity. I will present EMRI candidates that we have identified using multi-wave length studies of various classes of cosmic-transients including stellar tidal distribution events, quasi-periodic eruptions from nuclei of external galaxies, and active galactic nuclei (AGN)outbursts. I will present the case of them as EMRIs but will also discuss alternatives to explain the range of observed properties. I will also briefly mention our results on identifying newborn compact objects in supernovae, use of tidal disruption events to capture ultra fast outflows/jets and new ways to measure black hole spins.

Host: Prof. Mark Pitt

January 28

Friday 2:30pm
130 Hahn Hall North
Zoom Link
(poster)

Special Colloquium

Dr. Chris Ashall
(University of Hawaii)

"The Variety of Thermonuclear Supernova"

Type Ia Supernovae (SNe Ia) mark the demise of white dwarfs (WD). These cosmic explosions release as much luminous energy as the sun produces over its entire lifetime. As cauldrons of nucleo synthesis, SNe Ia provide the interstellar medium with Fe-group elements and are key to its isotopic composition. They are also accurate cosmological distance rulers, which were vital in the discovery of the acceleration of the Universe. Yet somehow the exact details of their progenitor scenario (e.g. single degenerate vs double degenerate) and explosion mechanism (e.g. Chandrasekhar mass vs. sub-Chandrasekhar mass) still eludes us. Understanding the origin of SNe Ia is critical if we are to reduce systematic in future cosmological experiments. All-sky surveys have helped to reveal more than nine sub-types of these thermonuclear SNe, and it is now clear that they have a diverse set of properties. I will provide an overview of these sub-classes, demonstrating how high precision multi-band follow-up observations allow for subtle differences to be revealed. These differences provide critical details about the origins of the explosions which were not previously known. I will particularly concentrate on the over luminous super-Chandrasekhar mass, normal, and sub-luminous SNe Ia. Finally, I will discuss how the James Webb Space Telescope and the Large Synoptic Survey Telescope will help solve the unknown SNe Ia progenitor scenario and explosion mechanism problems.

Host: Prof. Mark Pitt

January 31

Monday, 2:30pm
304 Robeson Hall
Zoom Link
(poster)

Special Colloquium

Dr. Luis Pedro Garcia
(Pintos, University of Maryland)

"Dynamics and Control of Quantum Systems"

In practice, quantum systems of interest are never isolated. The presence of noise or the interaction with an environment can radically change a system’s dynamics, typically destroying resources such as quantum coherence and entanglement – that is, destroying the resources that are necessary to benefit from quantum phenomena in applications of quantum science. I will present two general frameworks to study the dynamics of realistic quantum systems from first principles. More specifically, I will show conditions under which a system equilibrates rapidly, as well as bounds on the speed with which open-quantum and classical-stochastic systems evolve. In the last part of the talk, I will introduce a mechanism to control the dynamics of a quantum system by exploiting measurement feedback from continuous monitoring. This framework allows us to reproduce or to counteract the irreversible stochastic dynamics due to quantum measurements. I will show that this can, in turn, be used to mitigate the effects of the interactions with an environment.

Host: Prof. Mark Pitt

February 2022
February 4

Friday 2:30pm
130 Hahn Hall North
Zoom Link
(poster)

Special Colloquium

Dr. Burcin Mutlu-Pakdil
(University of Chicago)

"The Smallest and Faintest Galaxies: Clues to the Nature of Dark Matter and Galaxy Formation"

The smallest and faintest galaxies around the Milky Way are the most ancient, most metal-poor, and most dark-matter-dominated systems known. These extreme objects offer unique access to small scales where the stellar and dark matter content can be studied simultaneously. They hold the promise of major breakthroughs in understanding the nature of dark matter and a more complete picture of galaxy formation. Thus, their discovery and characterization are among the most important goals in the field. In this talk, I will share our ongoing observational efforts to detect these faint systems around the Milky Way and beyond, and upcoming advances in the era of deep and wide imaging instrumentation, with a focus on their implications.

Host: Prof. Mark Pitt

February 7

Monday, 2:30pm
304 Robeson Hall
Zoom Link
(poster)

Special Colloquium

Dr. Charles Kilpatrick
(Northwestern University)

"The Next Generation of Gravitational Wave Counterpart Discovery"

The promise of multi-messenger astronomy was spectacularly realized in 2017 by the detection of a binary neutron star merger, GW170817, simultaneously localized by LIGO/Virgo and telescopes observing at all wavelengths. This single event led to ground-breaking new discoveries in the physics of compact objects, synthesis of heavy elements, and even cosmology. The challenges of extending these discoveries to a large population of electromagnetic counterparts will require new observing and analysis techniques, instrumentation, and collaborations. On the heels of the seminal discovery of GW170817, I will discuss our results from the most recent LIGO/Virgo observing run to detect new gravitational wave counterparts and the ongoing efforts to rapidly coordinate a global networks of telescopes, identify optical transients, and characterize their explosion properties and eject a. I will then discuss new programs I am leading to extend search and follow up into the near- and mid-infrared where heavy element-rich events are brighter, including wide-field infrared searches, JWST imaging and spectra for well-localized counterparts, and a new Keck program to obtain near-IR spectra of hundreds of transients for comparison to candidate gravitational wave counterparts.

Host: Prof. Mark Pitt

February 11

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Special Colloquium

Dr. Charles Cao
(University of Maryland)

"Deciphering Quantum Gravity with Quantum Codes"

The real world is messy and noise is ubiquitous. In order to construct a practical quantum computer that can process quantum information reliably, one needs to account for the presence of noise during the course of computation. Quantum error correction codes are pivotal in making a fault-tolerant quantum computer as they help safeguard the fragile quantum information against the impact of noise. Surprisingly, beyond their applications in quantum computing, they have also made a profound impact at the juncture of quantum information, quantum many body physics, and gravity. In this talk, I will first provide a gentle introduction to quantum error correction codes. Then I will discuss how they can be intricately linked to some of the key aspects of quantum gravity where geometry and gravity may emerge from complex quantum systems.

Host: Prof. Mark Pitt

February 14

Monday, 2:30pm
304 Robeson Hall
Zoom Link

(poster)

Special Colloquium

Dr. David Nataf
(Johns Hopkins University)

"On the Milky Way’s Extinction Curve and Oldest Stellar Populations"

The study of Galactic astronomy is being revolutionized by the plethora of incredible data from various new surveys, facilities, and the use of modern probabilistic methods. In this talk of two parts, I first describe efforts to characterize the nature of the interstellar extinction curve, which dims and reddens the light of all distant stars and galaxies. I discuss applications for the study of extra solar planets in the inner Milky Way, in the context of NASA’s upcoming Nancy Grace Roman Space Telescope, and for the extra galactic distance scale, where the uncertainty in the extinction toward the Large Magellanic Cloud is equivalent to an uncertainty in Hubble’s Constant of 3 kilometers per second per mega-parsec. In the second part, I pivot to the study of the Milky Way’s (and Local Group’s) oldest stellar populations, specifically RR Lyrae stars and globular cluster stars. I discuss our ongoing efforts to better characterize RR Lyrae stars, and to study the contribution of globular cluster stars to the earliest epochs of star formation in the Milky Way. I conclude with a preview of an upcoming James Webb Space Telescope study of the Andromeda Galaxy, to compare its star formation history and chemical evolution to that of the Milky Way.

Host: Prof. Mark Pitt

February 21

Monday, 2:30pm
304 Robeson Hall
Zoom Link

(poster)

Special Colloquium

Dr. Filip Rozpedek
(University of Chicago)

"Quantum Internet: from proof-of-principle experiments to a robust service"

Quantum technologies offer novel possibilities for storing, processing, and transmitting information. Combining these functionalities into a network capable of exchanging quantum states between remote quantum processors will allow for creation of a Quantum Internet. Such future Quantum Internet will enable implementation of communication tasks in accessible to the classical Internet alone. This includes quantum-safe message encryption, as well as distributed quantum computing where multiple quantum computers can exchange quantum data in a similar way as classical computers exchange classical data over the Internet that we have today. In this talk I will introduce our vision for the future Quantum Internet and present an overview of the scientific efforts all over the world which aim to bring that vision into reality. I will then discuss the main challenges that we face in realizing that goal and review various solutions for overcoming them. These theoretical proposals will then be evaluated with respect to the state-of-the-art experiments on quantum networks and quantum communication. Finally, I will motivate how our knowledge and experience with classical communication network scan help us transform various proposed schemes for long-distance quantum information transfer into a reliable and robust Quantum Internet service.

Host: Prof. Mark Pitt

February 25

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Special Colloquium

Dr. Tianci Zhou
(MIT)

"Information Transport in Chaotic Quantum Dynamics"

Unitary quantum evolution of many-body systems remains an open challenge. Its complexity stems from chaos, which also bears thermalization. The pseudo-randomness by chaos provides a de-phasing mechanism so that some non-equilibrium behaviors can be understood in a classical picture. For an illustration, we deduce a phase diagram of information spreading in long-range chaotic systems, through a mapping to the soluble "long-range dispersal" in biophysics. The predicted long-time scaling is consistent with the numeric and coherence measurement from nuclear magnetic resonance. This paradigm also applies to other dynamical quantities such as the conventional auto-correlator,entanglement entropy and the fidelity scaling in the benchmark quantum computing experiments when errors and decoherence are present. It provides guidance for future experimental designs.

Host: Prof. Mark Pitt

February 28

Monday, 2:30pm
304 Robeson Hall
Zoom Link

(poster)

Special Colloquium

Dr. Qi Zhao
(University of Maryland)

"Towards Practical Quantum Simulation"

Quantum simulation is one of the most promising applications of quantum computers. In this talk, I will introduce my research on quantum simulation, including variational quantum simulation, digital quantum simulation algorithms, and the verification of quantum simulators. These works improve the understanding and the performance of quantum simulation and pave the way for the practical use of quantum simulation.

Host: Prof. Mark Pitt

March 2022
March 4

Friday 2:30pm
130 Hahn Hall North Zoom Link
(poster)

Prof. Royce Zia
(Physics, Virginia Tech & University of Houston)

"Understanding Complex Physical Systems -a glimpse into the topics awarded the2021 Nobel Prize in physics"

Last October, the Nobel Prize in physics was awarded to S.Manabe, K. Hasselmann, and G. Parisi “for groundbreaking contributions to our understanding of complex physical systems” - to quote the press release from the Royal Swedish Academy of Sciences. This talk will offer a very brief glimpse into what these physicists accomplished. After presenting a personal perspective of what a “complex physical system” is, I will share with you what I have learned about the two topics: (a) quantitative modelling of our climate and “fingerprinting” the source of global warming, and (b) formulating new techniques to deal with “frozen disorder” in a broad range of systems, from spin glass and protein folding to random lasers and the traveling salesman problem. I will also try to place these topics in the wider context of research into non-equilibrium statistical mechanics, an overarching framework for which remains to be established.

Host: Prof. Djordje Minic

March 11

Tuesday 4:00pm
Zoom Link
(poster)

Spring Break -No Colloquium


Host:

March 18

Friday 2:30pm
Zoom Link

(poster)

APS March Meeting Week -No Colloquium

Host:

March 25

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Prof. Edward Lyman
(University of Delaware)

“You are what you eat, or how I learned to stop worrying and love fat.”

Host: Prof. Rana Ashkar

April 2022
April 1

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Prof. Carl Mungan
(US Naval Academy)

Host: Prof. Tatsu Takeuchi

April 8

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Dr. Sara Barber
(U.S. House of Representatives)

" House Committee on Science, Space and Technology in 117th Congress"

Sara Barber works on the majority staff of the House Committee on Science, Space, and Technology. Her policy portfolio includes National Science Foundation oversight, STEM education, diversity/equity/inclusion in STEM, inter-agency R&D programs, and research policy issues such as sexual harassment, research security, and access to research data and publications. Sara came to the Hill in 2015 as an American Institute of Physics Congressional Science Fellow. She earned her PhD in physics from the University of Oklahoma that same year.

Host: Prof. Giti Khodaparast

April 15

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)


Host:

April 22

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Prof. Kenneth Schweizer
(University of Illinois)

.


Host: Prof. Shengfeng Cheng

April 29

Friday 2:30pm
130 Hahn Hall North
Zoom Link

(poster)

Prof. John Katsaras
(Oak Ridge National Laboratory)


Host: Prof. Rana Ashkar

May 2022

May 6
Friday 2:30pm
Zoom Link
(poster)

No Colloquium

Host:

Physics Department Colloquia

Fall 2021

Organizer: Vito Scarola

These meetings occur on Fridays from 2:30pm to 3:30pm in Hahn Hall 130 or/both
Virtual Meetings (unless otherwise indicated)

September 2021
September 10

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Edwin Barnes (Physics, Virginia Tech)

"Time Crystals and Quantum Computation"

Quantum non-equilibrium phases of matter can exhibit a variety of phenomena that have no counterpart in equilibrium settings. One such phase, known as a discrete time crystal, arises when a periodically driven system spontaneously breaks discrete time-translation invariance. In this phase, the quantum many-body state becomes insensitive to disorder and driving errors, provided interactions are sufficiently strong. I will describe the history and main concepts behind time crystals and related phases, present new examples of such phases, and show how they can be used to improve the performance of quantum computational tasks in quantum dot spin arrays.

Host: Prof. Mark Pitt

September 17

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Ian Shoemaker (Physics, Virginia Tech)

"Charting New Directions in the Landscape of Physics Beyond the Standard Model"

The existence of neutrino masses and non-luminous dark matter both require that the Standard Model of particle physics be extended. In this talk I'll discuss well-motivated theories which can account for these observations and how to go about testing them. A key theme emerging from the hunt for new physics is the complementarity of observational and experimental data.

Host: Prof. Mark Pitt

September24

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Thomas O'Donnell (Physics, Virginia Tech)

"The Hunt for Majorana Neutrinos: a Cold-Hearted Approach"

The discovery of neutrino mass in the first decade of the 21st century has spurred intense experimental effort to determine if Majorana masses and lepton-number-violating processes should be part of the new, extended Standard Model of particle physics. Neutrino less double-beta decay is a process with a relatively robust signature, which is hypothesized to occur if indeed neutrinos have Majorana masses. To observe it, large detectors with excellent energy resolution and very low backgrounds are required. CUORE, a cryogenic bolometer array operating near 10mK, is one such detector. In this talk I will describe the global effort to search for neutrino less double-beta decay, discuss the CUORE experiment, its unique cryogenic system, and some challenges of holding more than 1 tonne of material near absolute zero temperature.

Host: Prof. Mark Pitt

October 2021
October 1

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Fall Break No Colloquium

Host:

October 8

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Lawrence Weinstein (Old Dominion University)

"The Nucleons go two by two: Correlations in Nuclei"

Just like people, nucleons have different behaviors individually and when paired up. The typical individual nucleon (proton or neutron) orbits the nucleus in the mean-field potential of the other A-1 nucleons. However, when two nucleons get too close, the very strong short-range nuclear interaction can form them into close-proximity strongly correlated pairs. By studying these pairs, we can learn about the short-range part of the nuclear force, cold dense nuclear systems, and how the quark-gluon structure of nucleons is modified in nuclei.

Host: Prof. Camillo Mariani

October 15

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

No Colloquium

Host:

October 22

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

No Colloquium

Host:

October 29

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Dr. Matt Toups (Fermilab)

"Hunting Neutrino Anomalies with MicroBooNE "

Neutrinos are the most elusive fundamental constituents of matter. And yet these particles may hold the key to exotic new phenomena, which transcend our Standard Model of particle physics. In the last several decades neutrino oscillation experiments have given us a consistent picture of neutrino mass and mixing among three neutrino flavors. However, fundamental questions about the nature of the neutrino and matter itself remain unanswered. In addition, a series of anomalies, including an unexplained excess of electron-like events seen by the MiniBooNE experiment, hint at the existence of additional “sterile” neutrino flavors and complicate this simple picture. In order to improve on the previous generation of neutrino oscillation experiments and address these anomalies, new detector technologies are required. Liquid Argon time projection chambers (LArTPCs) promise to have the sensitivity and scale needed to chart this new territory. MicroBooNE is the first large-scale LArTPC detector built in the U.S. as part of the newly re-established Short Baseline Neutrino program at Fermilab, whose aim is to address the sterile neutrino hypothesis. In this talk, I will present results from the MicroBooNE’s first series of analyses investigating the anomalous excess of electron-like events seen by MiniBooNE.

Host: Prof. Camillo Mariani

November 2021
November 5

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. James Freericks (Georgetown University)

"Operator Mechanics: A New Form of Quantum Mechanics without Waves or Matrices "

Quantum mechanics was created with the matrix mechanics of Heisenberg, Born, and Jordan. Schroedinger’s wave mechanics shortly followed and allowed for simpler and more powerful calculations. Both Pauli and Dirac introduced a formulation of quantum mechanics based on operators and commutation relations, but it was never fully developed in the 1920’s. Instead, Schroedinger formulated the operator approach with his factorization method in 1940, which later was adopted by the high-energy community as super symmetric quantum mechanics in the 1980s.

Host: Prof. Tatsu Takeuchi

November 12

Friday 2:30pm
Virtual Meeting Only
(Zoom Link)
(poster)

Prof. Sarah Keller (University of Washington)

"Phase separation in living yeast membranes"

Equilibrium concepts like phase separation are rarely applied to living systems. However, since the 1960s, researchers have reported tantalizing hints that vacuole membranes in living yeast undergo phase separation at a particular point in the cell's growth cycle. Of course, proof of phase separation hinges on an observation of a reversible transition. Here, we provide that direct evidence. We then show that yeast actively tune the transition temperature to be close to the yeast's growth temperature, which implies that the membrane's proximity to the transition is important for the cell's function. Membrane phase separation is just as interesting when it is taken out of its cellular context, because it has the potential to reveal new physics. A persistent open question in the field is what physical mechanisms give rise to patterns of dots or stripes when membranes have excess area, whereas taut membranes separate into macroscopic phases. Here we show which aspects of current theories are supported by our data, and where opportunities lie for developing new models.

Host: Prof. Rana Ashkar

November 19

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Giorgio Gratta (Stanford University)

"Measuring gravity at micron scale and other fun tricks with optically levitated micro-spheres"

I will describe a new program of measurements in fundamental physics using optically levitated dielectric micro-spheres. The focus of the talk will be the recently completed first search for new, gravity-like interactions at micron scale using this novel technique. I will also show an array of other results, including searches for millicharged particles, Chameleon fields and techniques to manipulate the various degrees of freedom of the trapped micro-spheres.

Host: Prof. Camillo Mariani

November 26

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Thanksgiving Break - No Colloquium

Host:

December 2021
December 3

Friday 2:30pm
Virtual Meeting & 130 Hahn Hall North
(Zoom Link)
(poster)

Prof. Sara Majetich (Carnegie Mellon University)

"Super paramagnetic Tunnel Junctions for Probabilistic Computing"

Interacting nano magnets with low thermal stability have been proposed for probabilistic computing, which has potential uses in low power sensing and logic, encryption and decryption, and integer factorization [1]. The similarities and differences between super paramagnetic nano particles and electronically controlled super paramagnetic tunnel junctions will be reviewed, including a comparison of the Stoner-Wohlfarth asteroid and its tunnel junction equivalent. Next the differences between deterministic and probabilistic logic will be discussed. Boltzmann machines based on interacting spins, and how they achieve the lowest energy states with greatest statistical probability are described. By controlling the interaction strengths,probabilistic logic gates can be realized. Super paramagnetic tunnel junctions (SP-MTJs) are an ideal type of nano magnet because their time-averaged magnetization of the free layer can be programmed with a voltage or current [2, 3]. Fabrication of hard-wired magnetic tunnel junctions (MTJs) and incorporation in hybrid CMOS circuits are described. Experimental results for two example logic gates will be discussed: first the simple NOT gate formed from two coupled MTJs, and then a more complex AND gate made from three coupled MTJs. The feedback for the NOT gate leads to very high anti-correlations (~95%) and is nearly deterministic in behavior. With the AND gate, we start with a theoretical discussion of the feed back weightings, and corresponding Boltzmann factors for the probabilities of different micro states. The effect of pinning the output on in vertibility of the logic gates is shown in terms of energy levels and probabilities. Ametric based on pairwise comparison of micro state probabilities is proposed to quantify the performance of hardware-based probabilistic logic gates. This metric is applied to experimental results for our AND gate, and the impact of variations in MTJ performance is discussed. 1. K. Y. Camsari, et al., Phys. Rev. X 7, 031014 (2017). 2. M. Bapna and Sara A. Majetich, Appl. Phys. Lett. 111, 243107 (2017). 3. B. Parks, A. Abdelgawad, T. Wong, R.F. L. Evans, and S. A. Majetich, Phys. Rev. Applied 13, 014163 (2020).

Host: Prof. Satoru Emori

Physics Department Colloquia

Spring 2021

Organizer: Vito Scarola

These meetings occur on Fridays from 2:30pm to 3:30pm
Virtual Zoom Seminars (unless otherwise indicated)

January 2021
January 22

Friday 2:30pm
Virtual Zoom

(poster)

No Colloquium

(Faculty Meeting)

Host:

January 29

Friday 2:30pm
Zoom Link
(poster)

No Colloquium

(Faculty Meeting)

Host:

February 2021
February 5

Friday 2:30pm
Zoom Link
(poster)

No Colloquium

(Spring Break)

Host:

February 12

Friday 2:30pm
Zoom Link
(poster)

Prof. Tristan Hubsch (Howard University)

"The Dark Side of String Theory"

A closer reexamination of a family of toy models with a 3+1-dimensional de Sitter spacetime obtained in the standard low-energy limit of string theory reveals a host of novel features: On the phenomenological side, they predict several types of dark energy and dark matter, including a cosmological constant consistent with observations of the accelerated expansion of the Universe. These stem from cosmologically broken super symmetry, the inherent strong coupling of these models, and the ensuing involvement of additional, non-commutative, phase-space-like stringy degrees of freedom. The inclusion of these, hitherto ignored degrees of freedom also implies a natural seesaw-like solution to the hierarchy problem.

Host: Djordje Minic

February 19

Friday 2:30pm
Zoom Link

(poster)

No Colloquium

Host:

February 26

Friday 2:30pm
Zoom Link

(poster)

No Colloquium

Host:

March 2021
March 5

Friday 2:30pm
Zoom Link
(poster)

No Colloquium

Host:

March 9

Tuesday 4:00pm
Zoom Link
(poster)

Special Colloquium

Prof. Donna Strickland (University of Waterloo)

"Investigation of Multi-frequency Raman Generated Spectra"

Since the advent of lasers, many different nonlinear optical techniques have led to shorter, higher-intensity pulses. At Waterloo, we are studying Multi-frequency Raman generation (MRG), which efficiently generates a large number of Raman orders spanning the spectral region from the infrared to the ultraviolet. The band width of the Raman orders is sufficient to generate single-fem to second duration pulses. While the pulse duration is longer than what is possible with high order harmonic generation, the conversion efficiency is much higher. While most research in this field is concerned with making as many Raman orders as possible, we noticed that the spectra of the individual Raman orders changed dramatically when changing either the dispersion in the nonlinear medium or the laser pump intensity. In this talk, I will discuss the possible physical process causing these changes in the spectra as well as how the changes affect the generation of ultrashort intense pulses.

Host: Prof. Giti Khodaparast

March 12

Friday 2:30pm
Zoom Link

(poster)

No Colloquium


Host:

March 19

Friday 2:30pm
Zoom Link

(poster)

No Colloquium

(APS March Meeting)

Host:

March 26

Friday 2:30pm
Zoom Link
(poster)

Prof. Dejan Stojkovic (University of Buffalo)

"In Search of a Wormhole"

If a Traver-sable wormhole smoothly connects two different space times, then the flux cannot be separately conserved in any of these spaces individually. Then objects propagating in a vicinity of a wormhole in one space must feel influence of objects propagating in the other space. We show this in the cases of the scalar, electromagnetic, and gravitational field. The case of gravity is perhaps the most interesting. Namely, by studying the orbits of stars around the black hole at the center of our galaxy, we could soon tell if this black hole harbors a traversal wormhole. Alternatively, one can expect the same effect in black hole binary systems, or a black hole - star binary systems, which are actually the cleanest and most sensitive systems for such a search.

Host: Prof. Djorjde Minic

April 2021
April 2

Friday 2:30pm
Zoom Link

(poster)

No Colloquium

Awards Day Ceremony

Host:

April 9

Friday 1:00pm
Zoom Link

(poster)

Special Time

Prof. Margaret Gardel (University of Chicago)

"Design Principles of Morphorogenetic Matter"

My lab studies how the movement and shape of living cells is controlled by living materials constructed by protein assemblies within the cell interior. In this talk, I will describe my lab’s recent efforts to understand the design principles of the active, soft materials that drive morpho-genetic of epithelial tissue. In particular, we are interested in the design principles by which protein-based materials generate, relax, sense and adapt to mechanical force. Here I will describe our current experimental efforts using optogenetic approaches to study a morphogenetic ratchet controlling epithelial cell shape.

Host: Prof. Nadir Kaplan

April 16

Friday 2:30pm
Zoom Link

(poster)

Prof. Zvonimir Dogic (University of California)

"Assembly pathways and shape transitions of colloidal membrane"

In the presence of anon-adsorbing polymer, mono-disperse rod-like colloids assemble into one-rod-length thick liquid-like mono-layer, called colloidal membranes. The physics of these micron thick fluid-like assemblages are analogous to those of two-dimensional lipid bi-layers. However, their micron size allows for visualization of various membrane mediated interactions that are not possible using manometer-sized conventional membranes. Previous work on colloidal membranes has revealed new phenomena, such as chiral control of edge tension and assembly of finite sized fluid clusters. Using a colloidal membrane composed of rod-like molecules of differing lengths, we study how flat two-dimensional membranes fold into 3D structures. Above critical concentration of shorter rods flat 2Dmembranes become unstable and assume a bewildering variety of different shapes and topological. Simple arguments suggest that doping colloidal membranes with miscible shorter rods tunes the membrane’s Gaussian modulus, which in turn destabilizes flat 2D membranes

Host: Prof. Nadir Kaplan

April 23

Friday 2:30pm
Zoom Link

(poster)

Prof. Viola Priesemann (Gottingen and Georg August University)

“Statistical Physics of Spreading Dynamics: From Neural Networks to COVID-19”

How can we infer the spreading of activity if only a fraction of the system is observed? How can we then infer the spreading of activity in neural networks, and that of SARS-CoV-2 in the population? We recapitulate the basic principles of spreading dynamics, and its role in shaping collective computation in neural networks. For COVID-19, we show how it is mitigated by vaccination and test-trace-isolate strategies, and derive a metastable state, which could greatly facilitate the control of the pandemic.


Host: Prof. Uwe Tauber

April 30

Friday 2:30pm
Zoom Link

(poster)

Prof. Giorgio Gratta (Stanford University)

"Collective phenomena in a QD nuclear spin ensemble"

A coherent ensemble of spins interfaced with a fully controllable proxy qubit is an attractive platform to generate many-body entanglement and study out-of-equilibrium dynamics in a complex quantum system. Semiconductor quantum dots are a physical realization of such a toy system, where the electron spin can be operated both as a control and a probe over the dense ensemble of nuclear spins within the QD. This talk will introduce how we can engineer all-optically a “flip-flop” interaction term between the electron and the nuclei and control the interaction strength. Further, I will present our latest experimental progress on manipulating and characterizing the nuclear spin state, specifically the manifestation of sub radiance in optically tailored polarized nuclear states.


Host: Prof. Sophia Economou

May 2021

May 7
Friday 2:30pm
Zoom Link
(poster)

No Colloquium

Host: