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August 31

Penn State University

Title: Nuclear Astrophysics with Numerical Relativity

^{Abstract: Neutron star mergers and core-collapse supernovae are connected to some of the most pressing open questions in nuclear astrophysics, ranging from the physics of dense matter in neutron stars, to the origin of the heavy elements, to the mechanism powering stellar explosions. Multi-messenger observations of these events hold the key to unlock these mysteries. However, theory is needed to turn data into answers. In this talk, I will discuss our efforts to model neutron star mergers and supernovae in numerical relativity. I will talk about new developments in the simulation technology and recent results. Finally, I will talk about challenges and prospectives in this field.}

Host :  Veronica Dexheimer

Carnegie-Mellon University

Title: Magic Angle Butterfly in Twisted Trilayer Graphene

^{Abstract: Arranging two atomic monolayers of graphene on top of each other with a relative twist angle, results in the creation of a heterostructure that exhibits exceptional electronic properties. It was predicted theoretically in 2010 that such Twisted Bilayer Graphene hosts nearly flat electronic bands at the special twist angle dubbed the magic angle. In subsequent experiments the flat bands at the magic angle were confirmed and are believed to be a foundation for observed various interacting phenomena, such as an unconventional superconductivity and correlated insulating states. In this talk I will discuss recent experimental and theoretical efforts to understand and experimentally realize Twisted Trilayer Graphene — a heterostructure made of three graphene layers and characterized by two arbitrary twist angles. I'll show that this material hosts a plethora of magic angles (Magic Angle Butterfly) and can provide even better platform for new interesting interacting physics.}

Host: Khandker Quader

Thorsten Schmidt

ÐÔ¸£ÎåÔÂÌì University

Title: The Biophysics of Tightly Bent DNA

^{Abstract: DNA is the information storage molecule of all known life forms and can be used to build up almost arbitrary nanoarchitectures. While DNA is arguably the most studied and best understood biopolymer, things get more complicated when out of equilibrium. Unlike the idealized, straight, and relaxed textbook models, in biological contexts, DNA is under a highly dynamic bending stress and torque. Two meters of chromosomal DNA that every human cell holds, need to be compacted into a ten micrometer small nucleus without getting damaged or entangled, while remaining accessible to the molecular reading and copying enzymes. For these reasons, good physical DNA models are needed to understand the molecular processes that keep us alive. In this colloquium we will revisit some of the biophysical basics of DNA mechanics including the classical worm-like chain model and computational models. Our group investigates the mechanical behavior of tightly bent DNA and we are beginning to discover that some of our physical models might be incomplete or wrong for tightly bent DNA. More information: /physics/profile/thorsten-lars-schmidt}

Host: Khandker Quader

Florida State University/NHFML (National Magnet Lab)

Title: The Dark Energy of Quantum Materials

^{Abstract: The many correlated electron problems remain largely unsolved after decades; with one stunning success being BCS electron-phonon mediated conventional superconductivity. The Cooper pairing mechanisms of the dozens of families of unconventional superconductors, including the high-Tc cuprate, iron-based, and heavy fermion superconductors remain elusive and quite varied. But some of their fundamental characteristics are strikingly similar, including their ubiquitous phase diagram, with intriguing, correlated electron (non-Fermi liquid) phases that break the symmetry of their underlying lattice at temperatures well above Tc. These correlated phases remain among the greatest unsolved problems in physics; and I will present a fun analogy illustrating that. I will start with an overview of the US National MagLab and finish with a glimpse of some of my own recent work, identifying a possible new pairing mechanism in a heavy-fermion superconductor.}

Host: Khandker Quader

University of Massachusetts, Boston 

Title:  The Grasshopper Problem

^{Abstract: A grasshopper lands at a random point on a planar lawn of area one. It then makes one jump of fixed distance d in a random direction. What shape should the lawn be to maximize the chance that the grasshopper remains on the lawn after jumping? This easily stated yet hard to solve mathematical problem has intriguing connections to quantum information and statistical physics. A generalized version on the sphere can provide insight into a new class of Bell inequalities. A discrete version can be modeled by a spin system, representing a new class of statistical models with fixed-range interactions, where the range d can be large. I will show that, perhaps surprisingly, there is no d > 0 for which a disc shaped lawn is optimal. If the jump distance is smaller than the radius of the unit disc, the optimal lawn resembles a cogwheel, with transitions to more complex, disconnected shapes at larger d. Using parallel tempering Monte Carlo for the discrete spin model, several classes of optimal lawn shapes with different symmetry properties can be identified.}

Host: Khandker Quader

Indiana University, Bloomington

Title: Entangled Probes for Entangled Matter

Host: Khandker Quader

Canceled. To be re-scheduled.

Institute for Nuclear Theory, University of Washington

Title: Understanding QCD matter under extreme conditions with transport models

Host: Veronica Dexheimer

Canceled. Re-scheduled - Oct 26

Institute for Nuclear Theory, University of Washington

Title: Understanding QCD matter under extreme conditions with transport models

Host: Veronica Dexheimer

Xiaojun Yao

University of Washington, Seattle

Title: Eigenstate Thermalization in Non-Abelian Lattice Gauge Theories

^{Abstract: Understanding how an isolated quantum system thermalizes is an interesting and important physics question. On one hand, an initial pure state undergoing unitary time evolution preserves its purity and thus has zero entropy. On the other hand, a thermal state has a nonzero entropy, which seems to indicate an isolated quantum system will not thermalize. A paradigm of understanding this question is the eigenstate thermalization hypothesis (ETH), which states that matrix elements of local observables in the energy eigenstate basis are equal to the corresponding microcanonical ensemble values, up to corrections that decrease exponentially with the system size. Testing ETH for non-Abelian gauge theories is not only an interesting theoretical question, but may also help us to understand the initial stage of relativistic heavy ion collisions. In this talk, I will show results of testing this hypothesis for the 2+1 dimensional SU(2) non-Abelian gauge theory on a lattice. I will also discuss some future research ideas along this direction.}

Host: Mike Strickland

Texas A&M University

Title: Heavy Quarks and the Big Bang

^{Abstract: Quantum Chromodynamics (QCD) is the well-established theory of the strong nuclear force, with quarks and gluons as the elementary degrees of freedom. However, the emergence of its most prominent phenomena, i.e., the quark confinement into hadrons and the generation of hadronic mass, remains under intense investigation. Over the last two decades, another remarkable phenomenon has been discovered, namely the quark-gluon plasma (QGP), with transport properties that are often referred to as the ``most perfect liquid", close to conjectured limits set by quantum mechanics. The QGP last existed in the early universe, in the first few microseconds after the Big Bang. It is truly fascinating that this matter can be recreated 14 billion years later in laboratory experiments on Earth, by colliding heavy atomic nuclei at high energies. After an introduction to QCD and its phase diagram, the focus will be on the use of the heavy charm and bottom quarks to probe the QGP's properties. We will introduce a quantum many-body approach to the QGP that provides a basis for transport simulations aimed at describing heavy-flavor observables in heavy-ion collisions. A critical role in constraining the interactions in the QGP, which occur in the non-perturbative regime of QCD, is played by first-principles computations of the QCD, or "lattice QCD". We will highlight progress over the last decade in applications to heavy-flavor observables in heavy-ion collisions, where it appears that remnants of the confining force in the QGP are at the origin of its extraordinary transport properties. We also make the case for dedicated inter-institutional theory efforts to convert the experimental findings into robust knowledge of the QGP and its conversion into hadrons, as it happened in the Big Bang.}

Host: Mike Strickland

National High Magnetic Field Laboratory and Department of Physics, Florida State University

Title: Non-equilibrium transport and thermalization in two-dimensional bad conductors

^{Abstract: One of the most fundamental questions in physics is whether an isolated quantum many-body system thermalizes a long time after it is prepared far out of equilibrium. Recently, there has been a lot of interest in mechanisms that break ergodicity and lead to the absence of thermalization. In strongly disordered quantum systems, many-body localization (MBL) provides a robust mechanism for the failure of thermalization, but many questions remain open, especially in dimensions D >1. At the same time, experiments have been limited to mostly those on synthetic quantum matter, such as ultracold atoms in optical lattices and superconducting qubits, while observing the absence of thermalization in real, solid-state materials has been a challenge. This talk will describe the results of experimental studies of nonequilibrium dynamics in strongly disordered D=2 electron systems with power-law interactions µ1/ra and poor coupling to a thermal bath. We find that, for a=1, the system thermalizes, although the dynamics is glassy. The behavior of this Coulomb glass is similar to that of a large class of both 3D and 2D systems that are out of equilibrium (e.g., spin glasses, supercooled liquids). In contrast, for a=3, the thermalization is anomalously slow and strongly sensitive to coupling to the thermal bath, consistent with the proximity to a MBL phase. This direct observation of the MBL-like, prethermal regime in an electronic system thus clarifies the effects of the interaction range on the fate of glassy dynamics and MBL in 2D. These are important insights for theory, especially since the results have been obtained on systems that are much closer to a thermodynamic limit than synthetic quantum systems employed in previous studies of MBL. By establishing a new, versatile solid-state platform for the study of MBL, our work also opens new possibilities for further studies of ergodicity breaking and quantum entanglement in real materials.}

Host: Khandker Quader

Case Western Reserve University

Title: Super-resolution fluorescence imaging of extracellular environments

Host: Thorsten Schmidt