Colloquium
Fall 2021 Colloquia will be held in Room 307 of the Science and Engineering Research Facility (unless slated as virtual in the schedule below) on Mondays at 3:30 PM, EST.
Fall Colloquium Chair, Joon Sue Lee (jslee@utk.edu)
August 23 |
Ernest L. Brothers |
Graduate Student Association |
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August 30 |
Lorna Hollowell |
A Foundational Approach to Diversity |
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September 6 |
No Colloquium |
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September 13 |
Sergey Frolov |
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September 20 |
Jaan Mannik |
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September 27 |
Michael Lisa |
Hanbury Brown Twiss Interferometry: From the Stars, to STAR… and Back |
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October 4 |
Rolando Somma |
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October 11 |
NO COLLOQUIUM |
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October 18 |
Hanna Salman |
Cellular Memory in Bacteria and its Influence on Future Generations |
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October 25 |
Filip Ronning |
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November 1 |
P.E. Sokol |
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November 8 |
Antia Botana |
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November 15 |
Liang Fu |
Moire Metals and Semiconductors: New Frontier of Quantum Matter |
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November 22 |
Chris Rasmussen |
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November 29 |
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Ernest L. Brothers, Associate Dean, UT Graduate School and Director, Office of Graduate Training and Mentorship
This presentation is designed to give an overview of the definition of mentoring and the mentoring process. Participants will learn about the significance of faculty mentoring, mentoring vs. advising, and mentoring relationships. Participants will also be introduced to the phases of mentoring, a mentoring model, and learning about the benefits of cross-cultural mentoring and network mentoring.
Sergey Frolov, University of Pittsburgh
Please note: this colloquium is virtual. Contact cromeo@utk.edu for Zoom link.
Majorana particles are real solutions of the Dirac equation, representing their own antiparticles. In the condensed matter context, Majorana refers to electronic modes in nanostructures described by peculiar ‘pulled-apart’ wavefunctions and by hypothesized non-Abelian exchange. This last property makes them interesting for quantum computing. I will present our efforts to generate and verify Majorana modes in semiconductor nanowires coupled to superconductors. In particular, how can we tell Majorana signatures apart from similar Andreev states that do not have non-Abelian properties? While we may not have a verified Majorana observation now, I will talk about ways to get there: through careful experiments, improved nanowires and device fabrication and with eyes open for alternative explanations.
Jaan Mannik, Associate Professor, Department of Physics and Astronomy, The University of Tennessee, Knoxville
The code of life in all living organisms on Earth is DNA. DNA molecule is a polymer chain that comprises of A, T, G, C nucleobase monomers. The chain is typically about 1000 times longer than a characteristic dimension of a cell that hosts this molecule. How DNA molecule is compacted in a cell determines how its encoded information is retrieved and duplicated. A nuclear membrane encloses DNA molecules in our cells, but no nuclear membrane is present in bacteria. Nevertheless, DNA in a bacterial cell is compacted to a distinct cellular region termed the nucleoid, which occupies about half of the cell volume. Several processes have been proposed to contribute to DNA compaction, including looping and cross-linking DNA by proteins, twisting DNA to supercoils by molecular motors, transient DNA attachments to the cell membrane, and osmotic compression by macromolecular crowders. We have studied the role of macromolecular crowders in compacting the Escherichia coli nucleoid in live cells. Two sets of microfluidics experiments show that the nucleoid compacts as a non-linear spring as the concentration of cellular crowders increases. The length and width of the nucleoid decrease linearly first, but as the crowder concentration increases above 30% of the physiological level, the decrease abruptly stops. The nucleoid compression by crowders is anisotropic, being about five times lower along the short axes compared to the long axes of the cell. We found almost identical compressibility curves in two different growth conditions despite the ratio of protein to RNA-based cytosolic crowders differing by a factor of two. These experimental results suggest that the compaction is not sensitive to the composition of crowders. The latter conclusion is further supported by coarse-grained Brownian dynamics simulations and by free energy arguments. Altogether, our results support the idea that a diverse array of cytosolic proteins and stable RNA molecules are the main factors compacting the bacterial DNA to a distinct cellular entity that phase-separates from the rest of the cell. Equilibrium statistical physics appears thus to offer a sufficient framework to explain one of the main organizational principles in a bacterial cell.
Michael Lisa, Professor, Department of Physics, The Ohio State University
Seventy years ago, two radio engineers emerged from the frenzy of World War II and entered the new field of radio astronomy. Robert Hanbury Brown and Richard Twiss developed an entirely new instrument and technique, based on "correlated noise," to measure the angular radius of previously unresolvable stars. Initially greeted with skepticism, their work led directly to the birth of quantum optics. At nearly the same time, Goldhaber et al discovered a tiny unexpected correlation in the first true particle physics experiments; until recently, the "GGLP" effect played a minor role in particle physics. It would take another 15 years until the connection between these apparently disparate phenomena was realized by Shuryak and others around 1976, just as the new field of heavy ion physics was emerging. Thus did Hanbury Brown's discovery give birth to femtoscopy, the most direct method to probe space and time at the scales of 1e-15 meter and 1e-22 second. I will discuss the structures and insights that femtoscopy has revealed in ultra-relativistic ion collisions at RHIC and the LHC and their role in establishing the hydrodynamic nature of the quark-gluon plasma.
If time permits, I will discuss current progress to bring a high-energy physics approach to telescope arrays and relaunch stellar intensity interferometry with fast digital electronics and massive computing.
Rolando Somma, Los Alamos National Laboratory
Four decades ago, Richard Feynman envisioned that a main application of quantum computers will be "quantum simulation", that is, the simulation of the dynamics of quantum systems. Quantum simulation is ubiquitous in science but appears to be beyond the reach of classical computers. Not surprisingly, a lot of research in quantum computing has gone into developing methods for quantum simulation, but significant advances in this field were demonstrated only recently. In this colloquium, I will describe the quantum simulation problem in detail. Starting from the basics of quantum computing, I will show how quantum algorithms are constructed and then present a summary of the best quantum simulation methods known to date. I will also discuss some open problems that must be addressed to push practical quantum simulation closer to reality.
Hanna Salman, University of Pittsburgh
We study how cellular memory influences the cell’s properties and restrict heterogeneity in future generations. Heterogeneity in physical and functional characteristics of cells proliferates within a population due to stochasticity in intracellular biochemical processes and in the distribution of resources during divisions. It is limited, however, in part by the inheritance of cellular components between consecutive generations. In this talk I will present our new study in which, we characterize the dynamics of (non-genetic) inheritance in the simple bacterial model organism E. coli, and reveal how it contributes to regulating the various cellular properties (size, growth rate, etc.) in future generations. This is achieved using a novel microfluidic device that enables us to measure how two sister cells become different from each other over time. Our measurements provide the inheritance dynamics of different cellular properties, and the ‘inertia’ of cells to maintain these properties along time, i.e. cellular memory. We find that cellular memory is property specific and can last up to ∼10 generations. Our results can uncover mechanisms of non-genetic inheritance in bacteria and help develop quantitative description of cell progression and variation over time.
Filip Ronning, Los Alamos National Laboratory
Materials are the foundation of the world around us. New materials are important for developing new technologies, but they are also part of a materials multiverse - providing us with opportunities to explore new fundamental physics. Every material possesses a unique low energy Hamiltonian, and as such, is its own universe. f-electrons possess both strong Coulomb repulsions and strong spin orbit coupling. These properties lead to a rich variety of novel interactions, phases, and excitations. In this talk I will introduce how various fascinating physical phenomena emerge in f-electron materials, including heavy fermions, unconventional superconductors, spin liquids, topological Kondo insulators, Weyl semimetals, Majorana fermions, and the new physics we hope to discover. I will finish by describing how our exploration on novel f-electron materials has led to the discovery of very clean narrow band gap insulators, which we are attempting to develop into ultrasensitive light mass dark matter detectors.
P.E. Sokol, Indiana University
Quantum fluids have provided a unique “laboratory” for the study of strongly interacting assemblies of particles obeying quantum statistics. In particular, superfluid 4He exhibits interesting quantum phenomena, such as Bose condensation, which has recently been observed in other systems such as dilute gases and excitonic systems. These liquids have also occupied a central role as a model system for the study of critical phenomena, and even the birth of the Universe.
Recent attention has focused on the effects of disorder, induced by confinement, which has a profound effect on the macroscopic properties of the superfluid. The microscopic dynamics are fundamental to developing a complete picture of these unique liquids and the changes induced by disorder. Inelastic neutron scattering provides a powerful probe of these microscopic excitations. I will discuss measurements of the confined superfluid which show that much of the new macroscopic behavior can be understood in terms of the appearance of new microscopic excitations.
Antia Botana, Arizona State University
The physics behind high-temperature superconductivity in cuprates remains a defining problem in condensed matter physics. Among the myriad approaches to addressing this problem has been the study of alternative transition metal oxides with similar structures and electron count. After a 30 year quest, a non-cuprate compound with a cuprate-like structure that exhibits superconductivity has been found: hole-doped NdNiO2. Given that this material is one of the members of a larger series of layered nickelates, this result opens up the possibility of finding a new family of unconventional superconductors. By means of electronic structure calculations, we have analyzed the similarities and differences between this family of low-valence planar nickelates and cuprates. Even though these nickel oxide materials possess a combination of traits that are widely considered as crucial ingredients for superconductivity in cuprates (a square-planar nature, combined with the appropriate 3d-electron count, and a large orbital polarization) they also exhibit some important differences (a larger p-d energy splitting, and lack of magnetism in the parent compounds). Our results show that low-valence layered nickelates offer a new way of interrogating the cuprate phase diagram and are singularly promising candidates for unconventional superconductivity.
Liang Fu, MIT
This talk will survey recent advances in van der Waals heterostructures formed by stacking two layers of atomically thin materials. When the two layers have a small lattice mismatch or rotational misalignment, a long-wavelength moire structure emerges, which can produce entirely new electronic structures and quantum states of matter. I will describe the emergence of chiral spin texture and quantum anomalous Hall effect in semiconductor moire heterostructures, and propose a potential application of moire metals in catalysis, in particular, the production of hydrogen from water.
Chris Rasmussen, CERN
Antihydrogen—the antimatter equivalent of the hydrogen atom—is a unique platform for testing fundamental symmetries. In particular, CPT symmetry (Charge, Parity and Time) requires that the spectrum of antihydrogen be identical to its ordinary matter cousin. In the ALPHA experiment at CERN, antihydrogen atoms are synthesized and magnetically trapped to enable precise measurements and comparison to hydrogen. Recently, we have measured the 1S-2S transition with a relative error of just 2 parts in a trillion—the most precise direct measurement on an antimatter system to date.
Einstein’s weak equivalence principle (WEP) provides another prediction for antimatter which has yet to be tested experimentally: that the gravitational acceleration of antimatter should be equal to that of ordinary matter. ALPHA-g is a new experiment which will measure this acceleration directly through careful release of magnetically trapped antihydrogen atoms and recording of their annihilation positions.