Winter 2018 Colloquium Series
Date: Thursday, March 15th, 2018
Speaker: Robert F Klie, University of Illinois, Chicago
Title: Atomic-Resolution In-Situ Characterization of Multi-Functional Materials
Abstract: The last few years have seen a paradigm change in the way we characterize materials, with unprecedented improvements in both spatial and spectroscopic resolution being realized in current transmission electron microscopes (TEM). When multi-modal X-ray and electron imaging is combined with density-functional theory (DFT) calculations, the effects of defects, dopants or strain at grain boundaries or interfaces can now be directly determined and correlated to electronic/thermal transport properties. While spatial and energy resolutions better than 60 pm and 10 meV have been reported, aberration-corrected TEM has also enables a large variety of in-situ experiments at close to atomic resolution. Using this approach, the intercalation of multi-valent ions into cathode materials, the dynamics of vacancies, and the interactions between gases and nano-particles can now be directly observed, to only mention a few examples.
Here, I will demonstrate how in-situ multi-modal characterization and DFT modeling can be used to unravel the fundamental structure-property relationship of grain boundaries in photovoltaic CdTe devices or the intercalation of Mg-ions in transition metal oxide cathodes. I will further introduce a novel approach to measuring temperature and thermal expansion in nano-scale materials using electron microscope. I will also show how our recent development of graphene-based liquid cells now enables the direct characterization of biological materials and solid-liquid interfaces at close to atomic-resolution. I will conclude by discussing my vision for the future of high-resolution transmission electron microscopy, including monochromated electron-sources, new data processing approaches for low-dose microscopy as well as operando multi-modal methods combing x-ray and electron scattering.
Host: Ben McMorran
Date: Thursday, March 8th, 2018
Speaker: Mike Raymer, UO
Abstract: Given a single photon, information can be encoded on it using its color (frequency) or temporal shape (temporal mode). Nonlinear wave mixing in a strongly driven medium can exchange (or swap) the quantum states between two narrow spectral bands of the optical spectrum. When one spectral band is occupied by a single-photon wave-packet state, and the other band is occupied by vacuum, this process can achieve quantum frequency conversion (QFC), changing the carrier frequency of the photon. QFC can also act to time reverse the photon’s wave packet. Both of these operations play essential roles in creating a future quantum Internet.
Date: Thursday, March 1st, 2018
Speaker: Don M. Tucker, Ph.D, Professor of Psychology, Director of the Neuroinformatics Center, University of Oregon
Head of Clinical Science, Philips Neuro egi.com
CEO, NADA (Neural Analog-to-Digital Approximation) nadaweb.net
Abstract: The electroencephalogram or EEG has been an important research and clinical tool for the last 75 years. Recent advances in localizing the EEG to the electrical fields of the cortex have been achieved through dense electrode arrays, specifying the geometry of head tissues with MRI and CT, and measuring the conductivity of head tissues with electrical impedance tomogrphy (EIT). With bounded EIT (bEIT), we assume the geometry (from MRI) is known and need only to estimate the conductivity of each compartment. Small currents are injected into the head, recovered in the EEG signal, and the difference in amplitude is related to tissue conductivity of the model with Ohm’s law. My associates and I are exploring the possibility of understanding the pattern of cortical electrical fields through simulation, in which a whole brain artificial neural network model (thevirtualbrain.org) is created for to match the individual person’s fiber tractography (cerebral wiring diagram). Each node modeling the cortex is used to generate a simulated EEG field in proportion to its dynamic activity in the network model. Using machine learning to improve the emulation of the model of the individual’s cortical electrical fields over many weeks and months of recording, and extending the virtual brain with high performance computing, we will attempt to recreate the essential dynamics of the person’s brain in the artificial neural network model. Applications to be evaluated will include neurological diagnosis, educational analysis and remediation, and sharing memory between neural and machine intelligence.
Host: Mike Raymer
Date: Monday, February 19, 2018
Speaker: Michael Drewsen, Department of Physics and Astronomy, Aarhus University, Denmark
Abstract: In the recent past, the ability to control and manipulate trapped ions at the quantum level have gone through an amazing evolution. Based on laser cooling of trapped atomic ions, investigations of a wide range of fundamental quantum physics phenomena have been made possible, and today, laser-cooled and trapped ions constitute one of the most successful platforms for the quantum technology as well as optical atomic clock developments. The importance of these achievements is probably best exemplified by the Nobel Prize in Physics in 2012 to Prof. David Wineland, University of Oregon. Recently, the methods used to control and manipulate atomic ions has furthermore attracted attention from researchers interested in cold molecular science due to the potential of investigating the structure and internal dynamics of molecules at an unprecedented level of accuracy, as well as the prospects of studying Chemistry in unexplored cold and ultracold regimes. This field of research is still in its infancy, but holds great promises for the future.
In the talk, I will discuss some of my research group’s contributions to both quantum physics and chemistry based on cold and trapped ions.
Host: Mike Raymer
Date: Thursday, February 15, 2018
Speaker: Norbert Linke, Joint Quantum Institute, University of Maryland Department of Physics and National Institute of Standards and Technology
Abstract: Trapped ions are a promising candidate system to realize a scalable quantum computer. We present a modular quantum computing architecture comprised of a chain of 171Yb+ ions with individual Raman beam addressing and individual readout . We use the transverse modes of motion in the chain to produce entangling gates between any qubit pair. This creates a fully connected system which can be configured to run any sequence of single- and two-qubit gates, making it in effect an arbitrarily programmable quantum computer that does not suffer any swap-gate overhead .
Recent results from different quantum algorithms on five ions will be presented [3,4], including a quantum error detection protocol that fault-tolerantly encodes a logical qubit . I will also discuss current work with seven ions and ideas to scale up this architecture.
 S. Debnath et al., Nature 563:63 (2016).
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Host: Mike Raymer
Date: Thursday, February 8, 2018
Speaker: Jiehang Zhang, University of Maryland
Title: Quantum Many-Body Systems Engineered with Laser Light
Abstract: Quantum mechanics prescribes exponential scaling of the Hilbert space dimension in many-body systems, which presents both challenges and new opportunities for understanding strongly correlated matter, especially since novel custom-built systems are now available. I will describe such efforts on engineering quantum systems atom by atom, precisely controlling them with laser-driven interactions, and increasing the system size up to a regime where the capabilities of classical computers are challenged.
I will focus on the platform of trapped atomic ions, where a combination of excellent coherence time and high-fidelity measurements has enabled many applications, ranging from simulating condensed matter physics, to quantum computation. We represent spin qubits with electronic levels of ions in a Coulomb crystal, and entangle them through tailored laser pulses. I will present recent experiments using these systems to study dynamical phase with individual resolution for more than 50 spins, as well as non-equilibrium driven matter. I then conclude with future prospects.
Host: Mike Raymer
Date: Thursday, February 1, 2018
Speaker: Dalziel Wilson, IBM Research, Zurich
Abstract: Nanomechanical resonators are exquisite force sensors. In a new generation of experiments, they have even been used to “feel” the vacuum fluctuations of a laser field. This talk addresses the opposite side of the coin: can the same laser be used to “see” the vacuum fluctuations of the nanomechanical resonator? If so, can such a measurement be leveraged to cool a tangibly-sized mechanical object to its ground state, using feedback? I will describe an experiment designed to achieve both goals, based on a nanostring coupled to an optical microcavity. Along the way, I will show how this system can realize a position measurement with an imprecision 40 dB below that at the standard quantum limit, and “erase” part of the ensuing back-action using quantum noise correlations (a strategy of interest for future LIGO). I will also briefly describe a new class of nanomechanical resonators with room temperature quality factors exceeding 100 million. These devices undergo 100s of coherent oscillations before interacting with the thermal environment, and may enable new optomechanics-based quantum technologies.
- D. Wilson et. al., Nature 524, 325 (2015) 2. R. Schilling et. al., Phys. Rev. App. 5, 054019 (2016) 3. V. Sudhir et. al., Phys. Rev. X 7, 011001 (2017) 4. V. Sudhir et. al., Phys. Rev. X 7 (3), 031055 (2017) 5. A. Ghadimi et. al., arXiv:1711.06247 (2017)
Host: Mike Raymer
Date: Thursday, January 25, 2018
Speaker: David Allcock, NIST
Abstract: Entangled states of trapped ions are typically generated using laser-induced spin-motion coupling. Spin-motion coupling with hyperfine qubits has also been demonstrated with microwave magnetic fields instead of lasers, thus eliminating photon scattering errors and offering potential benefits for scalability. These experiments have relied on either static magnetic field gradients or oscillating magnetic field gradients at GHz frequencies [1-4]. We present methods of spin-motion coupling using magnetic field gradients oscillating at MHz frequencies. We entangle the internal states of two trapped 25Mg+ ions in a cryogenic microfabricated surface-electrode trap and characterize the Bell-state fidelity. These implementations offer important technical advantages over both the static-gradient and GHz-gradient techniques.
 Mintert and Wunderlich PRL 87, 257904 (2001)
 Weidt et al. PRL 117, 220501 (2016)
 Ospelkaus et al. Nature 476, 181 (2011)
 Harty et al. PRL 117, 140501 (2016)
Host: Mike Raymer
Date: Thursday, January 18, 2018
Speaker: Yiwen Chu, Yale University
Title: Quantum Acoustics with Superconducting Qubits
Abstract: The ability to engineer and manipulate different types of quantum mechanical objects allows us to take advantage of their unique properties and create useful hybrid technologies. Thus far, complex quantum states and exquisite quantum control have been demonstrated in systems ranging from trapped ions to superconducting resonators. Recently, there have been many efforts to extend these demonstrations to the motion of complex, macroscopic objects. These mechanical objects have important applications as quantum memories or transducers for measuring and connecting different types of quantum systems. In particular, there have been a few experiments that couple motion to nonlinear quantum objects such as superconducting qubits. This opens up the possibility of creating, storing, and manipulating non-Gaussian quantum states in mechanical degrees of freedom. However, before sophisticated quantum control of mechanical motion can be achieved, we must realize systems with long coherence times while maintaining a sufficient interaction strength. These systems should be implemented in a simple and robust manner that allows for increasing complexity and scalability in the future.
In this talk, I will describe our recent experiments demonstrating a high frequency bulk acoustic wave resonator that is strongly coupled to a superconducting qubit using piezoelectric transduction. Our device requires only simple fabrication methods, extends coherence times to many microseconds, and provides controllable access to a multitude of phonon modes. We use this system to demonstrate basic quantum operations on the coupled qubit-phonon system. I will also briefly describe our current efforts to further improve our electromechanical device, which will hopefully allow for advanced quantum protocols analogous to what has been shown in optical and microwave resonators, resulting in a novel resource for implementing hybrid quantum technologies.
Host: Mike Raymer
Date: Thursday, January 11, 2018
Speaker: Scott Fisher, UO
Title: Blending Teaching, Outreach, and Research into an Astronomical Amalgam
Abstract: In this colloquium Scott Fisher will present on his work in the Department of Physics. Different than a typical research presentation, in this talk Scott will describe his efforts in the realms of teaching, outreach, and research and show how he has blended these topics into a vibrant and fulfilling position within UO Physics. He will give an overview of his teaching (and outreach) style and discuss a few in class (and speaking to the public) techniques used in his general education ASTR-12x classes and public/K-12 programs. With respect to research, he will give a top-level overview of research activities, including a discussion of ongoing and future projects at Pine Mountain Observatory as well as a discussion of a recent publication on Galaxy Evolution. In particular he will highlight the work done by a team of undergraduate PHYS majors which led to an extremely rare first-author publication for one of our students.
Host: Mike Raymer