Spring 2021

Superconductivity in low-density Dirac materials

Speaker(s): 
Dr. Vladyslav Kozii
Dates: 
Tuesday, March 2, 2021 - 4:00pm

The experimental observation of superconductivity in doped semimetals and semiconductors, where the Fermi energy is comparable to or smaller than the characteristic phonon frequencies, is not captured by the standard lore. In this talk, I present a mechanism for superconductivity in low-density three-dimensional Dirac materials that are close to a 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...

"Quantum Advantage in Quantum-Limited Classical Optical Communications using NISQ Processors

Speaker(s): 
Dr. Kaushik Seshadreesan
Dates: 
Thursday, March 4, 2021 - 10:00am

Demonstrating quantum advantage using near-term, noisy intermediate-scale quantum (NISQ) processors is a topic of keen interest in quantum computing. In laser communication systems that operate in the quantum-limited weak signal regime, such as deep-space optical communications, it has been rigorously proven that there exists a fundamental gap in terms of capacity and decoding error probability between conventional receivers that detect received modulated optical pulses one at a time, and "joint detection" receivers that collectively process optical pulse sequences (codeword blocks) in the...

Shedding Light on the Enigma of High Temperature Superconductivity in Monolayer FeSe / SrTiO3

Speaker(s): 
Dr. Kyle Shen
Dates: 
Monday, March 1, 2021 - 4:00pm

Quantum materials host a vast array of emergent electronic phenomena, including high-temperature superconductivity, topological properties, and nanoscale charge / spin ordering. One of the challenges is to be able to precisely and deterministically manipulate their properties. To achieve this control, we employ molecular beam epitaxy (MBE) to synthesize artificial quantum materials with atomic layer precision, combined with angle-resolved photoemission spectroscopy (ARPES) which provides direct insights into the electronic structure. In particular, I will focus on...

Dr. Judy Wu, University of Houston (Pitt Chemistry Seminar)

Speaker(s): 
Judy Wu
Dates: 
Thursday, February 25, 2021 - 2:30pm

Title: Molecules in a Hurry to Escape Antiaromaticity

Abstract: Antiaromatic molecules, unless kinetically trapped, fused to aromatic frameworks, or stabilized by chemical modifications, often are short-lived and difficult to work with experimentally—they always find ways of escaping the state of being called “antiaromatic.” Cyclobutadiene, cyclopentadiene, pentalene, and other cyclic, π-conjugated compounds, with formal [4n] ring π-electrons, easily dimerize to get rid of antiaromaticity. Upon irradiation, benzene rather isomerize to fulvene and...

Laser Beyond the Standard Quantum Limit

  • By Samantha Whelpley
  • 5 February 2021

Research led by David Pekker was recently featured in an article on Gizmodo titled “Physicists are Reinventing the Laser”. The work was from Pekker’s paper titled “A New Quantum Limit on Laser Linewidth,” co-authored with Michael Hatridge, Chenxu Liu, Maria Mucci, Xi Cao, and Gurudev Dutt.

Their research finds that the Schawlow-Townes limit, an equation used to find the coherence time limit for lasers, is no longer an accurate estimate and that it can be possible to build more coherent lasers. Pekker and his coworkers found that by placing a valve on a laser to control the flow of protons, the laser’s coherence time can be extended beyond the Schawlow-Townes limit.

Why Engineers Should Care about Quantum Computing -- From Quantum Hardware to Programming

Speaker(s): 
Abraham Asfaw
Dates: 
Tuesday, February 9, 2021 - 11:00am

This talk will attempt to answer the question, "Why Should Engineers Care about Quantum Computation." In the talk, I will lay out key concepts and potential uses of quantum computers in quantum simulation and computation. As part of the discussion, I will emphasize the urgency of building a quantum-ready workforce, highlighting the relevance of training in engineering for building the physical quantum computing systems and understanding their potential applications. I will not assume knowledge of quantum mechanics and quantum computation, and will take a systems...

Yanan Dai Wins 2020 OCPA Outstanding Dissertation Award

  • By Jennifer Zheng
  • 3 February 2021

Congratulations to a recent graduate from Hrvoje Petek's group, Dr. Yanan Dai, for winning the 2020 International Organization of Chinese Physicists and Astronomers (OCPA) Outstanding Dissertation Award! In addition to this award, his dissertation, “Imaging Light with Photoelectrons on the Nano-Femto Scale,” was also recognized and reprinted in Springer-Nature.

Dr. Dai’s dissertation includes his work on ultrafast microscopy techniques and recent applications. These projects included his development of an ultrafast photoemission microscope with sub-10 femtosecond and nanometer spatiotemporal resolution, which was subsequently utilized to probe for and ultimately discover topological quasiparticles. Using ultrafast optics, Dr. Dai was able to probe and observe topological meron and skyrmion-like plasmonic quasiparticles as well as their dynamics during a phase transition. 

Using these observations and technological developments, he offers an analytical theory of how these newly observed quasiparticles and the microscopy techniques used to address them could have further research applications. 

A reprint of his dissertation can be found in Sprinter-Nature.

Dr. Moïra Hocevar, Institut Néel CNRS, France (CMU MSE Seminar)

Speaker(s): 
Dr. Moïra Hocevar
Dates: 
Friday, April 2, 2021 - 11:30am

Growth of Nanowires Heterostructures for Quantum Devices and Nanotechnology

Abstract: Nanowires are crystals with the morphology of a hair but ten thousand times smaller. They measure several microns in length and tens of nanometers in diameter. For the past twenty years, nanowires have been at the root of important breakthrough in both basic science and nanotechnology in a multitude of scientific areas. They are now commonly developed for transistor and sensor applications, light emitting diodes or solar cells. In quantum technologies, their unique properties enabled the development of bright single photon sources, spin quantum bits and nanomechanical resonators. We fabricate nanowires with crystalline semiconductor materials such as silicon which is the backbone of electronics or gallium arsenide, which emits light and is used to manufacture light emitting diodes. For a certain number of applications, it is necessary to juxtapose different semiconductors to form a heterostructure. Yet, creating heterostructures is not an easy task, especially in thin films. As different crystalline materials have different lattice parameters (distance between atoms), the lattice is strained at the junction (or interface) between two materials. This induces the formation of defects, among them dislocations which deteriorate the targeted physical properties. Thanks to their morphology, nanowires have more flexibility to release strain, preventing the formation of defects. Nanowires have the potential to host heterostructures that cannot be fabricated in standard technologies, enabling the discovery of new physical phenomena and the improvement of existing devices. During the seminar, I will present an overview of my ongoing research on nanowire heterostructures. The first part will be dedicated to embedding light emitters in silicon technology. Different semiconductor families or high-mismatch semiconductors are combined in nanowires. I will show how interfaces are built without structural defects, a prerequisite for optoelectronic devices [1]. Then, I will present superconductor-semiconductor nanowire hybrids. A particular focus will be on the development and study of Sn/InSb interfaces which have recently shown high potential for superconducting and topological quantum circuits [2]. Finally, I will present the development of an ultrasensitive tool to study the mechanical properties of nanowires using a focused electron beam [3].

[1] Beznasyuk et al (2020)

[2] Pendharkar et al (2020)

[3] Pairis et al (2019)

Biography: Moïra Hocevar is a researcher at CNRS Néel Institute in Grenoble since January 2015. She received an Engineering degree in Materials Science from INSA de Lyon in France (2004), a master degree in Environmental Science from Université Denis Diderot in Paris (2005) and her PhD in Electronics from INSA de Lyon in 2008. Prior to joining Néel Institute in Grenoble, she was a Marie Curie postdoctoral fellow at the Technical University of Delft in the Netherlands and a Nanoscience Foundation postdoctoral fellow in Grenoble. Her research focuses on creating novel nanowire heterostructures by molecular beam epitaxy and uncovering their unique physical properties using Mhigh-end characterization tools.

Dr. Patrick Rinke, Aalto University, Finland (CMU MSE Seminar)

Speaker(s): 
Dr. Patrick Rinke
Dates: 
Friday, February 12, 2021 - 11:30am

Data generation in materials science is often limited by the time it takes to perform experiments or simulations. To facilitate the exploration and characterization of complex materials, we have developed the Bayesian Optimization Structure Search (BOSS) code. BOSS uses an active learning technique that strategically samples the parameter space of material-science tasks be it experimental or computational. BOSS proposes new data acquisition points for maximum knowledge gain, balancing exploitation with exploration. I will demonstrate BOSS' smart and efficient data strategy for two examples...

Timothy Berkelbach (Columbia & Flatiron Institute)

Speaker(s): 
Timothy Berkelbach
Dates: 
Thursday, February 18, 2021 - 4:00pm

Ab initio wavefunction-based quantum chemistry represents a tantalizing alternative to density functional theory for problems in materials science, due to the former's ability to achieve high accuracy with systematic improvability. I will give an overview of our group's research efforts in this direction, describing theoretical and methodological developments at the periodic Hartree-Fock and post-Hartree-Fock levels (especially perturbation theory and coupled-cluster theory) and connections to popular Green's function-based techniques such as the random-phase...

Pages