Seminar

Abstract: The recent demonstration of quantum supremacy by Google is a first step towards the era of small to medium scale quantum computers. In this talk I will explain what the experiment accomplished and the theoretical work it is based on, as well as what it did not accomplish and the many theoretical and practical challenges that remain. I will also describe recent breakthroughs in the design of protocols for the testing and benchmarking of quantum computers, a task that has deep computational and philosophical implications. Specifically, this leads to protocols for scalable and...

Abstract: It has been widely appreciated that Heusler alloys (e.g., Co2MnSi) can be half-metallic, meaning that there is a gap for one spin state at the Fermi level. It is in principal possible to use this feature to generate currents that are 100% spin-polarized. Unfortunately, exploiting this characteristic in real devices, which necessarily include interfaces between dissimilar materials, represents a far greater challenge. This seminar will focus on observations about epitaxial Heusler alloys grown on GaAs and MgO. I will discuss why we are interested in the microwave...

Abstract: 2D materials are atomically thin nanostructures that are considered enabling elements in future electronics due to their unique geometry and exciting physical properties. To realize such applications, however, challenges in materials quality and production have to be addressed. In this talk we will first introduce a novel growth method that can enhance the scale, reliability, and controllability of 2D materials synthesis. Through control of the gas phase kinetics of the chemical vapor deposition process, efficient 2D materials growth could...

Abstract: Nanoscale photonic structures such as metamaterials and metasurfaces are enabling manipulation of light and heat in unprecedented ways. In this talk, I will present our research on shaping and controlling electromagnetic fields associated with thermal and mechanical applications. In the first part of my talk, I will present the work on tailoring high-temperature thermal emission by photonic elements that enable light recycling, relevant for high-efficiency heat-to-electricity energy harvesting. Next, I will show how nano-structured two-dimensional materials can...

Abstract: 

Dirac Matter: Over the last decade the concept of Dirac matter has emerged to the forefront of condensed matter physics. Prominent examples include the physics of the Dirac point in Graphene, Weyl points in topological semi-metals (TaAs) and edge states in topological insulators (Bi2Te3). These phases of matter are a playground for studying effects related to the Dirac equation and geometry of the electron wavefunction. We note, however, that they are defined only with respect to the properties of the electron (eg: bandstructure)....

Abstract: What is called "orthodox'' quantum mechanics, as presented in standard foundational discussions, relies on two substantive assumptions --- the projection postulate and the eigenvalue-eigenvector link --- that do not in fact play any part in practical applications of quantum mechanics. I argue for this conclusion on a number of grounds, but primarily on the grounds that the projection postulate fails correctly to account for repeated, continuous and unsharp measurements (all of which are standard in contemporary physics) and that the eigenvalue-eigenvector link implies that...

A fracton is an unusual new type of emergent quasiparticle found in various condensed matter systems.  Fractons are characterized by a set of mobility restrictions, which force isolated fractons to be strictly immobile, while certain bound states of fractons remain free to move.  This behavior leads to a variety of unusual phenomenology, such as non-ergodic and gravitational behavior, and may lead to advances in quantum memory storage.  In this talk, I will give a broad overview of the field of fractons, including both introductory material and recent advances.  I will describe the basics...

Joint Pitt/CMU Colloquium

Critical pattern formation at the Mott metal-insulator transition

Abstract:

I discuss the critical pattern formation of metallic and insulating nanoscale domains observed in NdNiO3 and VO2, via scanning near-field optical microscopy. The electronic phase transitions of these materials hold promise for novel ways to encode and process information, of interest for developing memristors and neuromorphic devices. Using theoretical tools from fractal mathematics and disordered statistical mechanics, we use the rich spatial information of this...

Joint Pitt/CMU Colloquium

Fractionalized excitations in the quantum Hall effect

Abstract:

One of the basic tenets of Condensed matter Physics is the classification of matter into phases exhibiting certain universal behaviour.  Examples of phases of matter include crystalline solid, superconductor, and ferromagnet.  A new class of materials was discovered in the recent decades, called topological phases, which challenges the conventional paradigms regarding phases of matter.  Contrast to the conventional phases, topological phases possess...

Abstract: IBM has been working on realizing a quantum computer since the idea first surfaced in 1982. Early instantiations were photon-based and proved that indeed bit like information could be stored in a quantum state. Since then many different modalities have sprung up, Trapped Ions and Superconducting qubits being the most popular. The IBM systems are on the path to error correction. However, we still have a long way to go. The path to success will be paved by wide scale acceptance and training in these using this new computational paradigm. All manner of expertise will be important on...