Past Colloquia

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

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

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

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

APS March Meeting Week -No Colloquium

Host:

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

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

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

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

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

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

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

Fall Break No Colloquium

Host:

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

Prof. Sowjanya Gollapinni (Los alamos National Laboratroy

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No Colloquium

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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

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

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

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

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

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

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

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

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

APS March Meeting Week -No Colloquium

Host:

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

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

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Prof. Kenneth Schweizer
(University of Illinois)

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Host: Prof. Shengfeng Cheng

Prof. John Katsaras
(Oak Ridge National Laboratory)

Host: Prof. Rana Ashkar

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

Fall Break No Colloquium

Host:

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

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

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

No Colloquium

(Faculty Meeting)

Host:

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

No Colloquium

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No Colloquium

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No Colloquium

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No Colloquium

(APS March Meeting)

Host:

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

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

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

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

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

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

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

Fall Break No Colloquium

Host:

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

No Colloquium

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No Colloquium

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No Colloquium(Tenure Track Physics)

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"Spring Break" (APS March Meeting)

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"Spring Break"

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No Colloquium ( Due to COVID-19)

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No Discussion Meeting (Due to COVID-19)

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No Colloquium (Due to COVID-19)

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No Colloquium (Due to COVID-19)

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Prof. James Wells (University of Michigan)

"Seeking clues on why matter won over anti-matter"

One of the most intriguing mysteries of nature is why there is more matter in the universe than anti-matter given that the basic laws of particle physics do not appear to allow for it. One promising direction of explanation attacks the conservation of baryon number, which I will argue is one of the most vulnerable principles in fundamental physics. Forthcoming proton decay and neutron oscillations experiments may reveal much about just how the universe managed to make us and not anti-us

Host: James Gray

Prof. Sylvain Veilleux (Physics, Virginia Tech)

The Cool Side of Galactic Winds

Galactic winds impactongoing star formation and black hole activity in their hosts and deposit massand energy into their halos and the intergalactic medium. Majoroutstanding questions remain, however, about the precise impact that galacticwinds make. In particular, the exact nature of the neutral and molecular gasphases in these winds is still unclear. This colloquium will highlight therecent discovery of powerful atomic and molecular winds in nearby galaxies andquantify the role of quasars in driving these winds.

Host: Nahum Arav

Prof. Alan Robock (Rutgers University)

"Climatic and Humanitarian Impacts of Nuclear War "

A nuclear war between any two nations, such as India and Pakistan, with each country using 50 Hiroshima-sized atom bombs as air bursts on urban areas, could inject 5 Tg of soot from the resulting fires into the stratosphere, so much smoke that the resulting climate change would be unprecedented in recorded human history. Our climate model simulations find that the smoke would absorb sunlight, making it dark, cold, and dry at Earth’s surface and produce global-scale ozone depletion, with enhanced ultraviolet radiation reaching the surface. The changes in temperature,precipitation, and sunlight from the climate model simulations, applied to crop models show that these perturbations would reduce global agricultural production of the major food crops for a decade. Since India and Pakistan now have more nuclear weapons with larger yields, and their cities are larger, even a war between them could produce emissions of 27 or even 47 Tg of soot. My current research project, being conducted jointly with scientists from the University of Colorado, Columbia University,and the National Center for Atmospheric Research, is examining in detail, with city firestorm and global climate models, various possible scenarios of nuclear war and their impacts on agriculture and the world food supply. Using six crop models we have simulated the global impacts on the major cereals for the 5 Tg case. The impact of the nuclear war simulated here, using much less than 1% of the global nuclear arsenal, could sentence a billion people now living marginal existences to starvation. By year 5, maize and wheat availability would decrease by 13% globally and by more than 20% in 71 countries with a cumulative population of 1.3 billion people. In view of increasing instability in South Asia, this study shows that a regional conflict using <1% of the worldwide nuclear arsenal could have adverse consequences for global food security unmatched in modern history. The greatest nuclear threat still comes from the United States and Russia. Even the reduced arsenals that remain in 2020 due to the New START Treaty threaten the world with nuclear winter. The world as we know it could end any day as a result of an accidental nuclear war between the United States and Russia. With temperatures plunging below freezing, crops would die and massive starvation could kill most of humanity. As a result of international negotiations pushed by civil society led by the International Campaign to Abolish Nuclear Weapons (ICAN), and referencing our work, the United Nations passed a Treaty to Ban Nuclear Weapons on July 7, 2017. On December 10, 2017, ICAN accepted the Nobel Peace Prize “for its work to draw attention to the catastrophic humanitarian consequences of any use of nuclear weapons and for its ground-breaking efforts to achieve a treaty-based prohibition of such weapons.” Will humanity now pressure the United States and the other eight nuclear nations to sign this treaty? The Physicists Coalition for Nuclear Threat Reduction is working to make that happen.

Host: Patrick Huber

Fall Break (No Colloquium)

Host: Vito Scarola

Prof. Hal Haggard (Bard College)

The Black Hole Spin Puzzle, Random Geometries, and Gravitational Wave Observations

Black hole entropy is a robust prediction of quantum gravity with no established phenomenological consequences to date. We use the Bekenstein-Hawking entropy formula and general-relativistic statistical mechanics to determine the probability distribution of random geometries uniformly sampled in phase space. We show that this statistics (in the limit hbar → 0) is relevant to large curvature perturbations, resulting in a population of primordial black holes with zero natal spin. In principle, the identification of such a population at LIGO, Virgo, and future gravitational wave observatories could provide the first observational evidence for the statistical nature of black hole entropy.

Host: Djordje Minic

Faculty Meeting ( No Colloquium)

Host: Vito Scarola

No Colloquium

Host: Vito Scarola

Thanksgiving Holiday (No Classes)

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Thanksgiving Holiday (No Classes)

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Prof. Shengfeng Cheng (Physics, Virginia Tech)

"Watching Paint Dry is Surprisingly Interesting"

The drying process of a soft matter solution such as a colloidal suspension or a polymer solution provides an excellent playground to explore nonequilibrium physics. One famous example is the coffee ring effect, where a spill of coffee (a particle-laden drop) after drying leaves a ring-like deposit at its perimeter. As another example, novel stratification phenomena have recently been discovered in polydisperse particle suspension films that undergo rapid drying. In all these processes, the interplay of solvent evaporation, fluid dynamics, diffusion, phoresis, and capillarity leads to far-from-equilibrium settings where rich phenomena emerge. In this talk, I will describe our effort of using large scale molecular dynamics (MD) simulations to study various soft matter solutions undergoing drying, including solutions of colloids, polymers, and their mixtures. The solvent is first modeled explicitly as a Lennard-Jones liquid. For bidisperse particle suspensions, a state diagram of stratification outcome is determined and the counterintuitive “small-on-top'” stratification, with an enrichment of the smaller particles at the receding liquid-vapor interface during fast drying, is observed. The diagram is compared to the predictions of several theoretical models recently proposed on the basis of diffusiophoresis. An approach to control stratification via thermal gradients and associated thermophoresis is proposed and validated with MD simulations. The explicit solvent is further mapped to an implicit, uniform, viscous medium by matching the diffusion coefficients of the particles as well as their pair correlation functions. A consistent stratification behavior is observed in both explicit and implicit solvent models under the same drying condition. We also apply our models to investigate the drying process of solutions of polymers and particle-polymer mixtures. Our results reveal a new strategy of unfirmly dispersing nanoparticles into a polymer matrix using fast solvent evaporation, interesting stratification phenomena in drying polyelectrolyte solutions, the formation of a variety of dry structures in drying films or droplets, and ways to control these structures via tuning drying conditions.

Host: Mark Pitt

Fall Break

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Prof. Vinh Nguyen (Physics, Virginia Tech)

"Quantum Coherence in Single Erbium Optical Centers in Seimconductors"

The incorporation of rare earth into semiconductors is of significant interest for optoelectronic devices, ranging from emitting elements in solid-state lasers and displays to optical fiber telecommunications and to quantum information processing. In this regard, erbium has been the prime candidate as its optical emission occurs at the technologically important wavelength of 1.5 µm, which is important for telecommunications, matching the absorption minimum of silica-based optical fibers. In the talk, I review optical properties of Er-doped gallium nitride (GaN:Er) thin films on silicon by metal-organic chemical vapor deposition, progress in the formation of laser gain media, and coherent control of the optical centers for quantum information processing. Initially, a p-i-n light emitting diode based on GaN:Er was fabricated and emission at 1.5 µm and in the green spectral region was observed. Subsequently, optical gain in GaN:Er thin films in an optically pumped configuration was demonstrated. Experiment data indicated that optical gain was enhanced through synthesis of multi-quantum well (MQW) structures including GaN:Er layers. Recently, we have demonstrated stimulated emission through optical pumping of specific Er centers in the MQW structures. The material has recently emerged as one of the potential candidates for quantum information processing thanks to its combination of atomic-line properties, optical and electrical excitation, and solid-state host environment. A hybrid approach has been demonstrated in which optical excitation is used to change the charge state of the erbium optical centers, and this change is then detected electrically. In addition, I propose an experimental approach to coherently control impurity wavefunctions associated with single erbium optical centers in semiconductors.

Host:Mark Pitt

Prof. Sophia Economou (Physics, Virginia Tech)

"Quantum Information Technologies: Quantum Networks, Near-term Processors and Algorithms"

Lately the field of Quantum Information Science and related technologies have attracted vigorous world-wide interest. These technologies include quantum computers that will be able to solve efficiently classes of important problems not accessible to classical computers, a new generation of sensors with improved sensitivity, and the ‘quantum internet’, an inherently secure network for communicating and accessing remote quantum computers securely. I will discuss the status of these technologies, showcase exciting advances, and present highlights from my group, including our work on quantum networks and on quantum algorithms for the simulation of chemistry problems with near-term quantum processors.

Host: Mark Pitt

Prof. Michael Schull (University of CO and UNC-Chapel Hill)

"Where do Galaxies End?

I will review recent observations and theoretical estimates of the spatial extent of galaxies. Galaxies are defined as systems of stars and gas embedded in extended halos of dark matter and formed by the infall of smaller systems. Their sizes are determined by gravitational structures, gas dynamics, and chemical enrichment in heavy elements produced by stars and blown into extragalactic space by galactic winds. The full extent of galaxies remains poorly determined. The “virial radius” and “gravitational radius” provide estimates of the separation between collapsed structures in dynamical equilibrium and external infalling matter. Other measurements come from X-ray emission and ultraviolet absorption lines from metal-enriched gas in galactic halos. Astronomers have now identified large reservoirs of baryonic matter in the circumgalactic medium (CGM) and intergalactic medium (IGM) that contain 50-70% of the cosmological baryons formed in the Big Bang. The extent of the bound gas and dark matter around galaxies such as our Milky Way is approximately 200 kpc (650,000 light years). Investigations of physical processes at the “edge of galaxies” are crucial for interpreting new observations of the CGM and IGM, and their role in sustaining the star formation in galaxies.

Host: Nahum Arav

Prof. Arjun Yodh (University of Pennsylvania)

“Phase Transitions, Relaxation and Shape Transformations in Soft Materials”

I will describe experiments that probe phase transitions and relaxation phenomena in colloid solids and super-cooled liquids, and shape transformations in liquid crystal drops. The experiments with colloids capture the mechanisms that facilitate crystal-crystal phase transitions and elucidate the origin of non-exponential relaxation in super-cooled liquids. Experiments with drops containing liquid crystal oligomers exhibit remarkable shape transitions which depend on temperature and oligomer chain distribution in surprising ways.

Host: Shengfeng Cheng

Prof. Jennifer Ross (Physics, Syracuse University)

“Self-Assembly and Self-Propulsion of Active Biological Elements”

Abstract: The cell is a complex autonomous machine taking in information, performing computations, and responding to the environment. Many of the internal structures and architecture is transient and created through active processes. Recent advances in active matter physics with biological elements are opening new insights into the physics behind how cellular organizations are generated, maintained, and destroyed. I will present two recent stories on two different topics at the interface between biological and soft matter physics. The first will discuss self-organization of microtubules in the presence of “weakly interacting” crosslinkers. The second will discuss possible mechanisms for the cell to mix itself using self-propelled single molecule enzymes. These works illustrate the importance of the fundamental physics to build structures and propel matter inside living cells while informing on new physics we can learn from biological elements and materials.

Host: Rana Ashkar

Thanksgiving Holiday (No Classes)

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