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Colloquia

Due to the Covid-19 pandemic all Fall 2020 and Spring 2021 Colloquia will be Virtual.

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

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)

Host: Prof. Djorjde Minic

April 2021
April 2

Friday 2:30pm
Zoom Link

(poster)

No Colloquium Awards Day Ceremony

Host:

April 9

Friday 2:30pm
Zoom Link

(poster)

Prof. Margaret Gardel (University of Chicago)

Host:Prof. Nadir Kaplan

April 16

Friday 2:30pm
Zoom Link

(poster)

Prof. Zvonimir Dogic (University of California)

Host: Nadir Kaplan

April 23

Friday 2:30pm
Zoom Link

(poster)

Prof. Viola Priesemann (Gottingen and Georg August Univresity)


Host: Prof. Uwe Tauber

April 30

Friday 2:30pm
Zoom Link

(poster)

Prof. Giorgio Gratta (Stanford University)


Host: Prof. Camillo Mariani

May 2021

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

No Colloquium

Host:

Physics Department Colloquia

Fall 2020

Organizer: Vito Scarola

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

September 2020
September 4

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

Prof. Camillo Mariani (Physics, Virginia Tech)

"Neutrinos-an Interesting Journey"

Neutrino physics has made tremendous strides in the past decade; the next challenge is to determine if neutrinos violate charge-parity (CP) symmetry, and to identify the neutrino mass hierarchy. The focus of my research group is to understand neutrino interactions in matter and their role in the discovery of the CP violating phase in the neutrino sector. Neutrino can also be used for other applications like nuclear reactor monitoring. The latter presents multiple experimental challenges, but there has been huge technology advancement in the last few years, one lead by a group at VT. More specifically, I will discuss our VT group research efforts preparing the next generation neutrino detectors and experiments. Throughout the talk we will rediscover the importance of nuclear physics and its influence in describing the neutrino interactions with matter.

Host: Mark Pitt

September 11

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

Prof. Vito Scarola (Physics, Virginia Tech)

Quantum Analog Simulation with Ultracold Atoms inOptical Lattices: Opportunities and Challenges

Quantum analog simulationoffers promise in effectively solving intractable quantum many-bodyproblems. One class of problems in particular, disordered Hubbard models,provide simple reduced models of strongly correlated materials, such as copperoxide-based compounds or disordered superconductors. Yet unbiasednumerical studies have not settled debates regarding the essential physicscaptured by Hubbard models. Progress in another seemingly unrelated areacan help with this mathematical problem. Cooling neutral atoms toquantum degeneracy has enabled the precise construction and manipulation oflarge multi-particle quantum states. Lasers defining opticallattices constrain the atoms so that their motion is very accurately capturedby Hubbard models. As a result, these experiments are being used toeffectively perform quantum analog simulation of Hubbard models. Work inmy theory group seeks to guide experimental setups in these simulations. I willreview experimental setups and discuss recent progress in using opticallattices as quantum analog simulators of Hubbard models.

Host: Mark Pitt

September 18

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

Prof. Tatsu Takeuchi (Physics, Virginia Tech)

"Successes and Failures in Theoretical Particle Physics"

I will review the history of the development of the Standard Model of Particle Physics during the past half-century or so, and the various theoretical ideas (the good,the bad, and the ugly) that were proposed in the process: some to be firmly established, while others, though quite popular in their heyday, have been proven wrong by experiment.

Host: Mark Pitt

September 25

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

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

October 2020
October 2

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

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

October 9

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

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

October 16

Friday 4:00pm
(Zoom Link) (poster)

Fall Break (No Colloquium)

Host: Vito Scarola

October 23

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

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

October 30

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

Faculty Meeting ( No Colloquium)

Host: Vito Scarola

November 2020
November 6

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

Prof. Arun Bansil (Northeastern University)

"Topological Quantum Phases, Novel Superconductors, and Ultra-Thin Films Beyond Graphene"

I will discuss some of our recent work aimed at understanding the electronic structure and spectroscopy of novel superconductors, topological materials, and atomically thin 2D films beyond graphene. [1-5] Illustrative examples will include: (i) How by exploiting electronic structure techniques we have been able to successfully predict and understand the characteristics of many new classes of topologically interesting materials, including magnetic topological materials; (ii) How atomically thin ‘beyond graphene’ 2D and layered materials offer exciting new possibilities for manipulating electronic structures and provide novel platforms for fundamental science and applications; And, (iii) with regard to the high-Tc’s, I will discuss recent breakthroughs in modeling the insulating pristine compounds and their transition from the insulating to the metallic state with doping without invoking any free parameters such as the Hubbard effective U parameter. A first-principles description of the competing stripe and magnetic phases in the cuprates also then becomes possible, providing a new pathway for modeling correlated materials more generally. [1] Y. Zhang et al., Proceedings of the National Academy of Sciences 117, 68 (2020). [2] A. Bansil, H. Lin and T. Das, Reviews of Modern Physics 88,021004 (2016). [3] C. Hu et al., Science Advances 6, eaba4275 (2020). [4] I. Belopolski etal., Science 365, 1278 (2019). [5] Z. Hennighausen etal., Nanoscale 11, 15929 (2019). Bio sketch of Professor Arun Bansil, Northeastern University Bansil is a University Distinguished Professor of physics at Northeastern University(NU). He served for over two years at the US Department of Energy managing the flagship Theoretical Condensed Matter Physics program (2008-10). He is an academic editor of the international Journal of Physics and Chemistry of Solids (1994-), the founding director of NU’s Advanced Scientific Computation Center (1999-) and serves on various international editorial boards and commissions. He has authored/co-authored over 400 technical articles and edited 17 volumes of conference proceedings covering a wide range of topics in condensed matter and materials physics, and a major book on X-Ray Compton Scattering (Oxford University Press, Oxford, 2004). Bansil is a Highly Cited Researcher (ISI Web of Science/Clarivate Analytics, 2017-2020).

Host: Kyungwha Park

November 13

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

No Colloquium

Host: Vito Scarola

November 20

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

No Colloquium

Host: Vito Scarola

November 27

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

Thanksgiving Holiday (No Classes)

Host:

November 29

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

Thanksgiving Holiday (No Classes)

Host:

December 2020
December 4

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

Prof. Bruce Vogelaar (Physics, Virginia Tech)

The CNO energy-production mechanism in the universe is detected by Borexino

An international team of about 100 scientists of the Borexino Collaboration reported in Nature this week a spectral measurement of neutrinos from the sun, directly revealing for the first time operation of the carbon-nitrogen-oxygen (CNO) fusion-cycle which is expected to be the dominant energy source powering stars heavier than the Sun. How this was accomplished will be explained, along the implications, and likelihood of even improved results. Some aspects of Virginia Tech's role just might be highlighted.

Host: Mark Pitt

December 11

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

Fall Semester Exams (No Colloquium)

Host: Vito Scarola/i>

December 18

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

University & Graduate Commencement Ceremonies
No Colloquium

Host: Vito Scarola
December 30

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

Holiday (No Classes)

Host: Vito Scarola
Physics Department Colloquia

Spring 2020

Organizer: Vito Scarola

These meetings occur on Fridays from 2:30pm to 3:30pm
130 Hahn Hall North or
Canceled Due to COVID-19 (unless otherwise indicated)

January 2020
January 24

Friday 2:30pm
130 Hahn Halll
(poster)

No Colloquium (Physics Faculty Meeting)

Host:

January 31

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

Special Colloquium

Prof. Alexandru Petrescu (University of Sherbrooke)

Quantum information processing with superconducting circuits: Purcell effect and the measurement problem

With recent advances in state preparation, gate, and measurement operations, superconducting circuit architectures are now leading candidates for quantum information processing. As micro-fabricated circuits are scaled up towards a practical quantum processor, strict requirements on the fidelity of operations required for quantum computation are imposed. For theorists, this mandates the development of accurate models describing the dynamics of complex superconducting circuits subject to strong drives. This talk will begin with an elementary introduction to such systems and their description in terms of quantum electrodynamics, the fundamental theory of light-matter interactions. We will then address the problem of the Purcell effect, which is the enhancement of the decay rate of a single qubit due to a linear electromagnetic environment, and show how convergent results can be obtained without any artificial high-frequency cutoffs. We will also explain how the Purcell rate is further enhanced in the presence of the drive fields typically used to measure qubits, which is a ubiquitous problem encountered in present-day experiments.

Host:

February 2020
February 7

Friday, 2:30pm
130 Hahn Hall
(poster)

Special Colloquium

Prof.l Giacomo Torlai (Flatiron Institute)

"Description:A Data-Driven Approach to Quantum Many-Body Physics "

Quantum many-body physics studies the collective properties of complex systems made of a large number of interacting particles. These may be real materials, quantum matter synthetically engineered in laboratories, as well as quantum computers and simulators. The challenge in uncovering their fundamental properties stems from the intrinsic complexity underlying quantum many-body states. This complexity is somewhat reminiscent of the so-called “curse of dimensionality” encountered in data science applications and routinely solved by machine learning algorithms, a disruptive technology which is now leading a profound revolution in the world of industry and information. In this talk, I will embrace a data-driven perspective on the ultimate “big data” problem in physics: the quantum wavefunction. Motivated by the remarkable experimental advances in producing high-quality quantum data, I will show how to repurpose generative neural networks to learn wavefunctions from measurements, and how these algorithms can be integrated in the experimental stack of quantum simulation platforms to enhance their capabilities. As a demonstration, I will present the reconstruction of a cold-atom wavefunction from experimental data produced by a programmable quantum simulator, including the extraction of its entanglement entropy. I will conclude by discussing what lies ahead in this new multidisciplinary field interfacing machine learning, computational physics and quantum information.

Host:

February 14

Friday 2:30pm
130 Hahn Hall
(poster)

Special Colloquium

Dr. Marie Boer (University of New Hampshire)

“Tomographic Views of Nucleon using Relativistic Light Particles”

The concept of atoms as elementary blocks of matter was born during antiquity. Last century, nuclear physics experiments discovered that atoms contain a nucleus made of positive and neutral particles, respectively called protons and neutrons (nucleons), themselves made of elementary particles, called quarks and gluons (partons). Quantum Chromodynamics is the theory describing parton interactions, where gluons are vector of the strong force between quarks, ensuring their confinement. The development of particle accelerators allowed for many experimental discoveries about this fundamental structure and led to models describing the distribution and dynamics of the partons inside the nucleon. Recent progress has allowed multi-dimensional representations, accounting for correlations between partons' spatial distributions and their momenta. In particular, Generalized Parton Distributions (GPDs) are probabilistic functions accessible from exclusive reactions, i. e. reactions where all products are known, in a kinematic regime where the partons can be probed individually. Interpretations of GPDs leads for instance to tomographic descriptions of the nucleon. In this presentation, I will review our current understanding of the nucleon structure and motivate more complex representations. As an example, I will discuss the potential of Compton-like scattering processes off quarks ("light scattering") for 3-dimensional tomographic views of the nucleon and for testing the fundamental properties of the GPDs. I will talk about several current and future experiments, in particular at the Jefferson Laboratory (Newport News, VA), and discuss their potential in challenging new measurements accessing GPDs

Host: Camillo Mariani

February 21

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

No Colloquium (Tenure Track Physics Faculty Meeting)

Host:

February 28

Friday 2:30pm
130 Hahn Hall

(poster)

No Colloquium(Tenure Track Physics)

Host:

March 2020
March 6

Friday 2:30pm
130 Hahn Hall

(poster)

"Spring Break" (APS March Meeting)

Host:

March 13

Friday, 2:30pm
130 Hahn Hall

(poster)

"Spring Break"

Host:

March 20

Friday 2:30pm
130 Hahn Hall North

(poster)

No Colloquium ( Due to COVID-19)

Host:

March 27

Friday 2:30pm
130 Hahn Hall

(poster)

No Discussion Meeting (Due to COVID-19)

Host:

April 2020
April 3

Friday 2:30pm
130 Hahn Hall

(poster)

No Colloquium (Due to COVID-19)

Host:

April 10

Friday 2:30pm
130 Hahn Hall


(poster)

No Colloquium (Due to COVID-19)

Host:

April 17

Friday 2:30pm
130 Hahn Hall

(poster)

No Colloquium (Due to COVID-19)

Host:

April 24

Friday 2:30pm
130 Hahn Hall

(poster)

No Colloquium (Due to COVID-19)

Host:

May 2020
May 1

Friday 2:30pm
130 Hahn Halll
(poster)

No Colloquium (Due to COVID-19)

Host:

May 8

Friday 2:30pm
130 Hahn Hall
(poster)

"Exam Day" (No Colloquium)

Host:

May 15

Monday, 2:30pm
130 Hahn Hall
(poster)

"University Commencement "(No Colloquium)

Host:
Physics Department Colloquia

Fall 2019

Organizer: Vito Scarola

These meetings occur on Fridays from 2:30pm to 3:30pm in 130 Hahn Hall North.
Refreshments are served at 2:15pm (unless otherwise indicated)

August 2019
August 30

Friday 2:30pm
210 Robeson Hall
(poster)

Host:

September 2019
September 6

Friday 2:30pm
210 Robeson Hall
(poster)

Host:

September 13

Friday 2:30pm
210 Robeson Hall
(poster)

Prof. Shunsaku Horiuchi (Physics, Virginia Tech)

"The Hunt for Dark Matter"

Four fifths of the matter in the universe consists of something completely different from the "ordinary matter" we know and love. I will explain why this "dark matter" is an unavoidable ingredient to understand the universe as we observe it, and I will introduce the strategies to search for dark matter as a particle. I will then focus on an example of a possible hint of discovery, and describe the importance of astrophysics to elucidate its validity. I will finish by outlining ways forward in this exciting hunt.

Host: Mark Pitt

September 20

Friday 2:30pm
210 Robeson Hall
(poster)

Dr. Mark Stiles (NIST, Gaithersburg, MD)

"Energy-Efficient Neuromorphic Computing with Magnetic Tunnel Junctions"

Human brains can solve many problems with orders of magnitude more energy efficiency than traditional computers. As the importance of such problems, like image, voice, and video recognition increases, so does the drive to develop computers that approach the energy efficiency of the brain. Magnetic devices, especially tunnel junctions, have several properties that make them attractive for such applications. Their conductance depends on the state of the ferromagnets making it easy to read information that is stored in their magnetic state. In addition, the spin current can manipulate the magnetic state. Based on this electrical control of the magnetic state, magnetic tunnel junctions are actively being developed for integration into CMOS integrated circuits to provide non-volatile memory. This development makes it feasible to consider other geometries that have different properties. I describe computing primitives that have been constructed based on the different functionalities of magnetic tunnel junctions. The first group of these uses tunnel junctions in their superparamagnetic state for a population coding scheme or for stochastic computing. The second uses them as non-linear oscillators in the first nanoscale “reservoir” for reservoir computing.

Host: Satoru Emori

September 27

Friday 2:30pm
210 Robeson Hall

(poster)

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

October 2019
October 4

Friday 2:30pm
210 Robeson Hall

(poster)

Fall Break

Host:

October 11

Friday 2:30pm
210 Robeson Hall

(poster)

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

October 18

Friday 2:30pm
210 Robeson Hall

(poster)

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

October 25

Friday 2:30pm
210 Robeson Hall

(poster)

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

November 2019
November 1

Friday 2:30pm
210 Robeson Hall

(poster)

Prof. Ewelina Hankiewicz (Theoretical Physics, University of Wurzgburg)

"Unconventional Superconductivity in Topological Insulators and Rashba 2DEGS"

A topological insulator in the proximity to an s-wave superconductor is the prefect material to detect signatures of Majorana fermions. S-wave superconductor on the top of the surface states of 3D TI generates s-wave and p-wave pairing mixture in the surface state due to the spin-momentum locking [1,2]. We predict that in the Josephson junction setup, namely superconductor (S) /surface state of topological insulator/superconductor (S), existence of this p-wave component leads to novel features in transport like superconducting Klein tunneling i.e. the perfect transmission of hybridized Majorana states for normal incidence, the non-sinusoidal current phase relation [2] and unusual phase-dependent thermal conductance [3]. Further, we propose the experimental setups to observe signatures of Majorana fermions in the ac Josephson effect on TI hybrid structures [4] and in phase controlled Josephson junctions based on Rashba 2DEGs [5,6]. [1] L. Fu and C. L. Kane, Phys. Rev. Lett. 100, 096407 (2008). [2] G. Tkachov and E. M. Hankiewicz, Phys. Rev. B 88, 075401 (2013). [3] B. Sothmann and E. M. Hankiewicz Phys. Rev. B 94, 081407(R) (2016); B. Sothmann, F. Giazotto, and E. M. Hankiewicz New J. Phys. 19, 023056 (2017). [4] F. Dominguez, O. Kashuba, E. Bocquillon, J. Wiedenmann, R. S. Deacon, T. M. Klapwijk, G. Platero, L. W. Molenkamp, B. Trauzettel, and E. M. Hankiewicz Phys. Rev. B 95, 195430 (2017). [5] H. Ren, F. Pientka, S. Hart, A. T. Pierce, M. Kosowsky, L. Lunczer, R. Schlereth, B. Scharf, E. M. Hankiewicz, L. W. Molenkamp, B. I. Halperin and A. Yacoby, Nature 569, 93(2019). [6] B. Scharf, F. Pientka, H. Ren, A. Yacoby, and E. M. Hankiewicz Phys. Rev. B 99, 214503 (2019).

Host: Giti Khodaparast

November 8

Friday 2:30pm
210 Robeson Hall


(poster)

Prof. Rodney D. Van Meter Keio University

"The quantum Internet"

The Quantum Internet will transform how we communicate, compute and measure our universe. Using long-distance entanglement, we can execute cryptographic functions that strengthen the security of classical communications, measure physical phenomena more precisely than purely classical systems, and ultimately couple quantum computers together to extend the size of problems they can solve. But how can we build such a network? Experimental progress toward quantum repeaters -- the quantum equivalent of the Internet's switches and routers -- is moving at a dizzying rate, and theorists have proposed half a dozen approaches to managing errors to create high-fidelity entanglement along a chain of repeaters. The next frontier is extending from one-dimensional chains to complex topologies, and on to a network of networks -- a true Quantum Internet. In this talk, I will bridge the physics and the engineering to give a picture of the current status and open research problems.

Host: Sophia Economou

November 15

Friday 2:30pm
130 Hahn Hall North

(poster)

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

November 22

Friday 2:30pm
130 Hahn Hall North

(poster)

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

November 29

Friday 2:30pm
210 Robeson Hall

(poster)

Thanksgiving Holiday (No Classes)

Host:

December 2019
December 6

Friday 2:30pm
210 Robeson Hall
(poster)

Prof. Bhuvana Srinivasan (Aerospace & Ocean Engineering, Virginia Tech)

“Numerical Studies of High-energy Density Fusion and Astrophysical Plasma's”

Experimental efforts to study nuclear fusion and astrophysical plasmas have produced significant scientific advances but remain challenged by diagnostic access and limitations.  Hence, there is a need for high-fidelity computational models in plasma physics to support experiments.  Plasma physics will be introduced in this talk along with a brief description of plasma models and their limitations. Recent advances in plasma fluid and kinetic modeling have supported development of sophisticated simulation tools. A hierarchy of models, ranging from magnetohydrodynamic (MHD) to fully kinetic, are developed and applied across a wide range of parameter regimes in the Plasma Dynamics Computational Laboratory at Virginia Tech. Some representative applications will be presented with a focus on high-energy-density plasmas for fusion and astrophysical studies.  Other research topics being pursued in the computational laboratory will be discussed briefly.

Host: Nahum Arav

December 13

Friday 2:30pm
210 Robeson Hall
(poster)

Exam Day (No Classes)

Host:

December 20

Friday 2:30pm
210 Robeson Hall
(poster)

University and Graduate Ceremonies (No Classes)

Host:
December 27

Friday 2:30pm
210 Robeson Hall
(poster)

Holiday (No Classes)

Host:
December 30

Friday 2:30pm
210 Robeson Hall
(poster)

Holiday (No Classes)

Host: