Fall 2017

2D Materials - A New Platform for Strong Light-Matter Interactions

Speaker(s): 
Ajit Srivastava
Dates: 
Thursday, November 16, 2017 - 4:30pm

A recent addition to low-dimensional materials are monolayer transition metal dichalcogenides (TMDs), such as WSe2, with an atomically thin, honeycomb lattice and optical band gaps. In addition to spin, charge carriers in TMDs exhibit a “valley” degree of freedom, which can be optically addressed using circularly polarized light, opening up exciting possibilities for “valleytronics". Another curious aspect of TMDs lies in the non-trivial geometry of their band structure which gives rise to equal but opposite Berry curvature, an effective magnetic field in the momentum...

American Leadership in Quantum Technology

  • By Burcu Ozden
  • 10 November 2017

On October 24, 2017 house committee on science, space, and technology held hearings on “American Leadership in Quantum Technology QT.” The goal of the hearing was to provide audiences the view of United States’ (US) and other nations’ research and development efforts to develop quantum computing and related technologies, and to identify what more can be done to robust these efforts. For this regard, committee members made their opening statements on quantum technology and US leadership in this area.  Witnesses from National Institute of Standards and Technology (NIST), National Science Foundation (NSF), Department of Energy (DOE), IBM, National Photonic Initiative, and Argon National Lab were emphasized the importance of study and research in quantum information science and technology to sustain the leadership in this area.

Quantum technologies at the dawn of the second machine age

Speaker(s): 
Pedram Roushan
Dates: 
Friday, December 1, 2017 - 4:00pm

Quantum theory, formed in the early part of the last century, has revolutionized our view on the nature of physical reality.  More than half a century after its inception, a few great minds of physics, including Richard Feynman, predicted that the laws of quantum mechanics could give rise to a computing paradigm that is far superior to classical computing for certain tasks. Decades have passed since their great insight, but controlling fragile quantum systems well enough to implement even the most primitive quantum computer has proven difficult. One possible way of...

Spectral signatures of many-body localization with interacting photons

Speaker(s): 
Pedram Roushan
Dates: 
Thursday, November 30, 2017 - 4:30pm

Statistical mechanics is founded on the assumption that a system can reach thermal equilibrium, regardless of the starting state. Interactions between particles facilitate thermalization, but, can interacting systems always equilibrate regardless of parameter values? The energy spectrum of a system can answer this question and reveal the nature of the underlying phases. However, most experimental techniques only indirectly probe the many-body energy spectrum. Using a chain of nine superconducting qubits, we implement a novel technique for directly resolving the energy...

Kater Murch (Washington University in St. Louis): Quantum Thermodynamics with Superconducting Qubits

The laws of thermodynamics are fundamental laws of nature that classify energy changes for macroscopic systems as work performed by external driving and heat exchanged with the environment. In the past decades, these principles have been successfully extended to the level of classical trajectories of microscopic systems to account for thermal fluctuations. In particular, experimentally tested generalizations of the second law, known as fluctuation theorems, quantify the occurrence of negative entropy production. The extension of thermodynamics to include quantum fluctuations faces unique challenges such as the proper identification of heat and work and clarification of the role of quantum coherence. I will present experiments that allow us to track heat and work along single quantum trajectories of a superconducting qubit evolving under continuous unitary evolution and measurement. We are able to verify the first law of thermodynamics in that the measured heat and work sum to the total energy change of the quantum system.  We then verify the second law of thermodynamics in the form of the Jarzynski equality by employing a novel quantum feedback loop that cancels the heat exchanged at each point in time with additional work.  Our results successfully generalize stochastic thermodynamics to the quantum regime, paving the way for future experimental and theoretical investigations of quantum information and thermodynamics.

Federal Funding: Multidisciplinary University Research Initiative (MURI)

Speaker(s): 
Ryan Champagne
Dates: 
Tuesday, November 14, 2017 - 12:00pm to 1:00pm

Researchers may gain a competitive edge when applying to prestigious annual programs like the Multidisciplinary University Research Initiative (MURI) through advance planning and connecting with appropriate program officers.

This workshop provides history and insights into the MURI program and will act as a starting point for interested researchers to strategize a competitive concept paper. 

Please complete this brief (3 question) survey before the session. Contact Ryan Champagne ...

The Ability to Electrically Tune the Dimensionality of mesoscopic LAO/STO Channels

  • By Burcu Ozden
  • 27 October 2017

In this work, authors used conductive atomic force microscope (c-AFM) lithography in which the conduction is controlled by surface protons that are distributed on the LAO surface. They have created two conducting channel with varying witdhs as 10 and 200nm on a  LAO/STO heterostructures grown by pulsed-laser deposition. They designed the the devices in a way that two conducting channels connected in series with two leads and voltage probes. By using silver epoxy on the bottom of the STO substrate they created contacts for a back gate voltage. They investigated changes in the magnetotransport properties on the channels with different widths by varying back gate voltage and applied magnetic field. They measured the conductance for both narrow and wide channels and demonstarted the hysteresis of both channels with back gating. Saturation of the conductance at higher gate voltages was also shown. They were able to demonstrate dimensional crossover from 2d to 1D behavior with their magnetoconductance measurements.



Quantum materials: Where many paths meet

  • By Leena Aggarwal
  • 27 October 2017

In Nature, there exist materials with exotic properties that cannot be understood in the framework of classical theories. Such properties, however, are beautifully described by more sophisticated theoretical tools involving quantum mechanics.  Such materials are now known as the “quantum materials”. The range of exotic properties exhibited by the quantum materials is extremely broad and includes superconductivity, superfluidity, ferromagnetism, quantum hall effect, spin-liquidity, topological insulation, to name a few.

Superconductors, discovered by Kammerlingh Onnes, 1911, were first to emerge as quantum materials. In normal metals, the resistance arises due to inelastic scattering between the charge carriers (electrons) and defects in the periodic crystal lattice. The defects or scattering centres can be any distortion to the periodicity of the lattice like those due to presence of impurity or the thermal vibration of the lattice points. In superconductors, surprisingly, the resistance becomes zero despite the presence of a large number of impurities and at high temperatures where the lattice points can undergo vigorous thermal vibration. The question that how the charge carriers remained insensitive to such strong scattering centres could not be answered within any classical picture. A microscopic understanding of superconductivity was first provided by Bardeen, Cooper and Schrieffer (BCS) in 1951, only after substantial development of quantum mechanics and quantum field theories – the theories where quantum mechanics is combined with Einstein’s theory of relativity.

New Technique for Measuring the Layer-Resolved Charge Density

  • By Burcu Ozden
  • 25 October 2017

Recently Benjamin M. Hunt and his colleagues developed a new technique for measuring the layer-resolved charge density, from which they can map layer polarization of the valley or spin quantum numbers in bilayer graphine and other two dimensional materials. In this study, they demonstrated direct measurement of valley and orbital levels in bilayer graphite. They have detected that the four valley and orbital components have different weights on the two layers of the bilayer. By using Hunt’s technique one can probe layer, valley, and spin polarization quantitatively in other atomic layered materials, including twisted bilayer graphene and both homobilayer and heterobilayer of transition metal dichalcogenide

 

The new era of Polariton condensates

  • By Leena Aggarwal
  • 17 October 2017

In a recently published paper in Physics Today, David Snoke, a professor of physics and astronomy at the University of Pittsburgh and Jonathan Keeling who is a reader in theoretical condensed-matter physics at the University of St. Andrews in Scotland, have shown the superfluidity of light where photon treats as a gas of interacting bosonic atoms. They have demonstrated that how to engineer a Bose–Einstein condensation from light.

 

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