PHYSICS COLLOQUIUM Spring 2024

Brian Skinner (Ohio State University)

Title: Measurement-induced Phase Transitions in the Dynamics of Quantum Entanglement

Abstract: When a quantum system evolves under unitary dynamics, as produced by either a Hamiltonian or by a sequence of gates inside a quantum computer, its various component parts tend to become more entangled with each other. Making measurements, on the other hand, tends to reduce this entanglement by collapsing some of the system's degrees of freedom. In this talk I'll consider what happens to the entanglement when a quantum many-body system undergoes both unitary evolution and sporadic measurements. I'll show that the competition between these two effects leads to a new kind of dynamical phase transition, such that when the measurement rate is lower than a critical value the dynamics is "entangling", while a higher-than-critical measurement rate leads to a "disentangling" phase. I will discuss our work demonstrating the existence of this transition, as well as more recent efforts to find exact solutions for its critical properties.

Host: Khandker Quader

Feb 8

Danny Caballero (Michigan State)    

Title: Supporting the integration of numerical computing in physics education

Host: Hamza Balci

Yashar Komijani (U. Cincinatti)

Title: Critical charge fluctuations in magnetic environments

Abstract: Quantum electronic matter has long been understood in terms of two limiting behaviors of electrons: one of delocalized metallic states, and the other of localized magnetic states. Heavy fermions are miniature high-Tc superconductors whose small energy scales provide the possibility of tuning the ground state between these two limits. This enables access to the strange metallic behavior which develops at the brink of localization, a phenomenon that has remained one of the enigmas of the condensed matter physics. The interest in this metallic state stems from its remarkable simplicity which masks the underlying complexity of an actual material and also its pivotal role as a parent state for high temperature superconductivity. In this talk, I will highlight some of the recent experiments in heavy fermions that point toward the universality of strange metals and yet challenge the prevailing understanding of the past three decades. They reveal that this peculiar physics exists not only in antiferromagnetic environments, but also in ferromagnetic settings, and involves singular fluctuations not only in magnetization but also in electronic charge and lattice degrees of freedom. Lastly, I will give an overview of some of the attempts to map out the phase diagram of heavy-fermions using the dynamical large-N method and the Schwinger boson representation of the spins. These efforts underscore the ongoing quest to unravel the complexities of quantum electronic matter, offering fresh insights into the fundamental nature of strange metals.

Host: Maxim Dzero

Andrew D. Hanlon (Carnegie-Mellon University)

Title: Uncovering the Nature of Strongly Interacting Matter

Abstract: Quantum chromodynamics (QCD) was introduced 50 years ago as the theory of the strong interaction. It has been exceptionally successful at describing a wide array of physical phenomena involving strongly-interacting matter. Still, there remain several challenges relating the underlying theory of QCD to experiment in various regimes. For instance, in low-energy scattering experiments, there have been a staggering number of hadronic resonances discovered that evade a complete theoretical understanding. In this regime, one can utilize lattice QCD, which is a systematically-improvable, first-principles, numerical method. Calculations within the extreme densities that exist in e.g. neutron stars, however, cannot be performed using QCD directly. Fortunately, tools like lattice QCD, which are robust at low densities, can be used in conjunction with effective field theory and many-body methods to extrapolate to higher densities. In this talk, I will provide evidence that lattice QCD, along with experiment and other theoretical methods, is an essential tool for making progress in connecting theory to experiment.

João Barata (Brookhaven National Laboratory)

Title: Resolving the Structure and Dynamics of QCD from Jets to Quantum Machines

Gerardo Ortiz (U. Indiana)    

Title:  Quantum Entanglement Microscopy

Abstract: In 2022 the Royal Swedish Academy of Sciences recognized groundbreaking experiments showing that quantum entanglement is an inherent property of our physical world with broad and potential implications in areas such as secure information transfer, quantum computing and sensing technologies. We will take a journey through the Science and Technology of the “spooky action at a distance” that perturbed Albert Einstein and was epitomized in a famous inequality by John Bell. We will then focus on the design of quantum entangled probes to uncover the inherent entanglement of matter, a discipline we might call “Quantum Entanglement Microscopy”. We have experimentally realized entangled neutron beams where individual neutrons can be entangled in spin, trajectory, and energy. Interestingly, by carefully tuning the probe's entanglement and inherent coherence properties, one can directly access the intrinsic entanglement of the target material. Our theoretical framework supports the view that an entangled beam of quantum particles, such as neutrons, X-rays, or photon-pairs, can be utilized as a multipurpose scientific tool. 

Host: Khandker Quader

Special Colloquium

Kirill Boguslavski (TU Vienna)

Title: Deciphering the dynamics of the Quark-Gluon plasma

Abstract: In relativistic heavy-ion collisions, a quark-gluon plasma (QGP) is formed. Governed by Quantum Chromodynamics, the QGP emerges as a fundamental aspect of the Standard Model of particle physics and has likely existed in the earliest instants of our universe. Phenomenological investigations reveal a rapid transition of the plasma into a nearly-perfect fluid within mere yoctoseconds, showcasing its intriguing behavior. The pre-equilibrium evolution of the QGP, leading to this fluid-like state, encompasses a rich variety of phenomena important for interpreting heavy-ion collision data. In this colloquium, we delve into some of the less understood aspects of the pre-equilibrium QGP dynamics. Specifically, we explore nonperturbative collective excitations, universal dynamics, and innovative strategies aimed at deciphering the initial stages using experimental probes such as jets and heavy quarks. Through these discussions, we aim to shed light on the fundamental properties of the QGP and its implications for high-energy physics.

Ayyalusamy Ramamoorthy (Florida State Univ. NHFML )

Title: Structural Studies of Membrane Proteins Using NMR and Nanodiscs

Abstract: 

Host: Thorsten Schmidt

Vlad Kozii (Carnegie Mellon University)   

Title: Superconductivity at low density

Abstract: Superconductivity – the loss of all electrical resistance at very low temperature – is one of the most remarkable quantum phenomena found in materials. The explanation of conventional superconductivity as a condensate of electron pairs constitutes a great triumph of 20th century solid state physics. In this conventional theory of superconductivity, the attraction that keeps the electron pairs together is provided by lattice vibrations, which provides an excellent description of many classical superconductors. This theory breaks down, however, when applied to unconventional superconductors discovered more recently. The failure of the conventional approach is particularly acute in materials with low – or very low – electron density. In this talk, I present a mechanism for superconductivity in a special class of low-density systems, i.e., the three-dimensional topological materials, which are close to a polar structural instability represented by the ferroelectric quantum critical point. I show that while the Coulomb repulsion between electrons is strongly screened by the lattice polarization near the critical point, the electron-phonon coupling is significantly increased by critical fluctuations, even in the case of vanishing carrier density. Applying these results to low-density systems, I show that the superconducting transition temperature is greatly increased upon approaching the quantum critical point. Furthermore, I will describe how ferroelectricity and topology may lead to superconductivity even at zero density.

Host: Maxim Dzero

Special Colloquium

Xiaojian Du (University of Santiago de Compostela, Spain)

Title: Non-equilibrium QCD matter

ONLINE COLLOQUIUM

https://us06web.zoom.us/j/85077670619?pwd=I5Tus8qDGPVS5K3b6tRywayE4NXCVF.1
Password: 322867

Abstract: Non-equilibrium systems and their thermalization are omnipresent. Quark-gluon plasma (QGP), a non-abelian plasma predicted by quantum chromodynamics (QCD) is of particular interest given that its equilibration occurs in nature only during the first few microseconds after the Big Bang. Relativistic heavy-ion collisions (HICs) are the only experiments that can produce this non-equilibrium QCD matter in the laboratory. We will talk about the thermalization of the QCD matter and its application in heavy-ion collision phenomenology. These include QCD turbulence, hydrodynamization and attractor in the thermalization of the QCD plasma, non-equilibrium di-lepton production, heavy quark thermalization, and quantum computing realization.

Shuang Zhu (Umass-Armherst)

CANCELLED