The Department of Physics and Astronomy Colloquium is held on Monday afternoons at 4:15 pm in room SLH 102 unless otherwise noted. Refreshments are served at 4:00 pm.

Spring 2014

January 13

Metaphotonics: Form vs Function

Nader Engheta

View Abstract

As the fields of metamaterials and nanophotonics reach certain levels of development, new directions and novel vistas appear on the horizon. Modularization, parameterization and functionalization of metamaterials and nanoscale photonics may provide new optical characteristics and functionalities for the platforms of metaphotonics. Indeed, metamaterial “forms” lead to “functions”. These include (a) the extreme-parameter nanophotonics, (b) materials that may function as optical nanocircuits (“optical metatronics” -- a platform for nanoscale information processing), (c) graphene metamaterials as one-atom-thick optical devices, (d) nanomaterials that perform mathematical operations (nanoscale analog computers), (e) nonreciprocal nanostructures for unusual flow of photons, and (f) metamaterial “bits” and “bytes” as building blocks for digital metamaterials, to name a few. In my group we are investigating a variety of features and properties of these concepts and directions in functionalizing metamaterials, and are exploring new classes of phenomena and potential applications. I will discuss some of these topics, present our latest results, and forecast future directions and possibilities.

January 27

Confinement and Processing Effects on Glassy Polymer Properties: Nanoparticles and Nanostructured Films

Rodney D. Priestley

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While the physics of polymer glasses has been an active area of research for decades, the subject remains rich in a multitude of phenomena that are not fully understood. In this talk, we discuss two important themes in contemporary polymer glass science: nanoscale confinement effects on material properties and new routes to the vitreous state. Concerning the former, significant effort has been devoted to pursing an understanding of the glass transition temperature and associated dynamics of polymers confined to the nanoscale. Much of our understanding has been obtained via studies on thin polymer films. Nevertheless, studies on polymers confined to other geometries are becoming increasingly more important as we pursue questions difficult to address using thin films. We have investigated confined polymer properties utilizing nanoparticles to elucidate commonalities or fundamental differences in the deviations of glassy properties from the bulk, despite different confining geometries. Our work suggests a common origin of size effects of the glassy properties of confined polymers, irrespective of geometry, that is, interfacial effects. Furthermore, nanoparticles, as we will illustrate, offer the possibility for unique measurements at the nanoscale that would be difficult to achieve with thin films. With regards to the later theme, the general process to forming polymer glasses is by cooling from the melt. This route to the vitreous state, although known for centuries, offers limited possibility to tune glassy properties. In starting from the gas phase to make glassy materials, we are able to generate nanostructured amorphous materials formed via the assembly of molecular-scale building blocks. In comparison to the conventional glass, these nanostructured materials can have superior thermal stability (40 K enhancement in glass transition temperature), factor of 300 increase in kinetic stability as well as a 40 % reduction in density. Individually, each of these property changes is exceptional. When viewed as a whole, the combination of properties for these amorphous materials makes them truly unique.

February 3

How do you teach Reynolds Number to a 4th grader? and Why is it good for you?

Tara Chklovski

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Iridescent is a science education nonprofit that helps scientists and engineers communicate their research to children and parents through open- ended engineering projects. Over the past 7 years, Iridescent has helped more than 1400 STEM experts inspire and equip ~ 21,000 children and their parents - across the US - and globally.

The founder, Tara, will share lessons, developing and scaling a program that helps scientists communicate their research to the public without dumbing down the concepts. Scientists develop their own creativity and understanding, while children develop domain knowledge, curiosity, creativity, persistence and problem solving skills. Iridescent has also developed a robust technology-based infrastructure that helps scientists broaden the impact of their work through a web and mobile interface, Curiosity Machine. Through this interface, scientists share videos of their work, children share videos of the projects they have worked on (based on the scientist's work) and get one on one feedback from the scientists on how to improve their project. The Curiosity Machine thus enables a scientist to share her work with thousands of children worldwide and support them in active learning and creation.

"It's funny how things I taught in Family Science always seem to pop up in my life. People think I'm a genius for understanding Reynolds number on such a fundamental level, but really, I know it because I taught it to a bunch of 4th graders."

February 10

Power of Adiabatic Quantum Computation

Itay Hen

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The paradigm of Adiabatic Quantum Computation (AQC) is a simple yet intriguing approach to problem solving on a quantum computer. Unlike the leading paradigm of quantum computing, namely the circuit model, AQC is an analog, continuous-time, method that does not require the design and use of quantum gates and therefore may be considered easier to implement. In this talk I will discuss the performance of certain novel quantum-adiabatic algorithms that have known analogues in the circuit model, and present results that demonstrate the computational power of AQC. I will also briefly discuss the practical importance of these results.

February 17
No colloquium (PRESIDENTS DAY)

February 24

Geometry and Topology of an Intracellular Membrane

Greg Huber

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"I seemed to see the membraneous and cylindrical tubes tremble beneath the undulation of the waters." [Jules Verne (describing Captain Nemo's underwater garden in 20,000 Leagues Under the Sea)]

The endoplasmic reticulum (ER) has long been considered an exceedingly important and complex cellular organelle in eukaryotes (like you). It is a network that threads its way outward, from the cell's nucleus all the way to its periphery. For over sixty years, microscopists have seen amazing things in the ultrastructure of the ER, and the complexity of its shape has inspired various picturesque characterizations: tubules, sheets, spheres, lamellae, cisternae, flattened vesicles. Despite the elegant physics of bilayer membranes offered by the work of Helfrich and Canham, as far as the ER is concerned, physical theory has mostly sat on the sidelines. However, refined imaging of the ER has recently revealed beautiful and subtle geometrical forms -- almost "simple" geometries, from the mathematician's point of view -- which some have called a "parking garage for ribosomes". Rather than being a mere footnote for physicists, these structures suggest answers to classic, long-standing questions: What is the structure of the entire organelle? How does it form? and Why did it evolve?

March 3
No colloquium (APS March Meeting)

March 10

Tailoring properties of single layer materials: looking beyond graphene

Talat Rahman
University of Central Florida

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Single-layer Molybdenum disulfide (MoS2) appears to be a promising material for next generation nanoscale applications because of its low-dimensionality and intrinsic direct band-gap of about 1.9 eV. Several experimental groups have reported novel electronic and transport properties which place this material beyond graphene for device applications. Efforts are underway to further tune these properties through alloying, defects, doping, and coupling to substrate. In this talk I will present results from joint theoretical and experimental investigations [1,2] which provide a framework for manipulating the functionality of this wundermaterial and take us closer to the goal of rational material design. My emphasis will be optical and catalytic properties of single layer MoS2 and its possible technological applications.

[1] D. Sun, et al., "An MoSx Structure with High Affinity for Adsorbate Interaction," Angew. Chem. Int. Ed. 51, 10284 (2012).
[2] D. Le and T. S. Rahman, "Joined edges in MoS2: metallic and half-metallic wires," J. Phys.: Condens. Matter 25, 312201 (2013).

March 17
No colloquium (SPRING BREAK)

March 24

Water on the edge: hydrogen bonding through the looking glass of surface-selective vibrational spectroscopy

Alex Benderskii

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The properties of water near surfaces and interfaces play important role in processes ranging from atmospheric chemistry to catalysis and biophysics. This talk will review the surface-selective vibrational sum frequency generation (VSFG) spectroscopy as a probe of the hydrogen bond network of water, focusing in particular on the air-water interface. Water's two intrinsic vibrational modes, stretch and bend, both report on the hydrogen bonding. The talk will present some of the experimental challenges/solutions for obtaining these spectra and review the current state of theoretical models and computer simulations that analyze the line shapes. In particular, we will focus on the "free OH" species of water molecules straddling the interface, which probe hydrogen bonds in the first mono-layer of waters, and compare these with bulk water H-bonds.

March 31

Single photons: From fundamental physics to quantum information

Elizabeth Goldschmidt

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The fundamentally quantum nature of single photons makes them ideally suited for many applications both exploring the core principles of quantum mechanics and implementing quantum information technologies. However, real single photon sources and detectors are not the ideal quantum systems we would want for these applications. Designing single photon technologies for a wide variety of quantum information schemes is thus a major effort in the field. I will discuss current research at NIST on single photon sources and detectors for quantum information applications including photon number resolving detection, generating indistinguishable photons, and coherently storing single photons. I will place this work in the context of the long history of related experimental work using single photons to study fundamental quantum phenomena.

April 7
No Colloquium
. .

April 14

Spectroscopy of many-body systems with a cold atom quantum simulator

Wes Campbell

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A lattice of strongly-interacting quantum spins may be simulated effectively on a classical supercomputer as long as the number of spins N is sufficiently small (20-50, depending upon the interaction model). Past this point, the size of the potential state space accessible to the system (which grows exponentially with N) requires too much memory, and we seek new methods to examine the crossover from the few-body to many-body regimes. A quantum simulator is a device that is in principle capable of simulating these systems in this regime because it has access to its own exponentially-large Hilbert space. I will describe work using a quantum simulator made from trapped atomic ions to simulate strongly-coupled quantum systems, and describe new methods for performing spectroscopy on the many-body system. I will also discuss progress toward implementing other quantum simulations with a collection of cold polar molecules.

April 21

Seismic tomography of the Earth's interior: methodology and current research

Cooper Harris
Earth Sciences

View Abstract

Seismic tomography is a valuable imaging tool used to investigate otherwise inaccessible deep Earth Structure. The basic technique is highly similar to computer-aided tomography (CAT scans) but is applied over much larger spatial and temporal scales. Seismic energy emitted from large earthquakes can be traced through the Earth’s mantle from its source to a seismic receiver. Specific seismic phases (namely P and S waves) are manually detected on seismograms and their arrival times are compared to those predicted by an accurate albeit simplified Earth model wherein velocity is depended only upon depth. Perturbations from expected travel-time measurements can be attributed to lateral heterogeneities in the Earth’s structure; these perturbations can be directly correlated to temperature, which affects density and thereby the propagation rate of waves. My talk will address how these temperature anomalies are interpreted after reviewing some basic background knowledge of geophysics. I will then explore the theories behind seismic tomography with special attention being given to multi-channel cross-correlation techniques and finite frequency sensitivity kernels. I will conclude by discussing my current research project to image the upper mantle beneath the Caribbean Sea Plate and show examples from a prior study on the Western United States by USC Postdoctoral Researcher, Dr. Rob Porritt.

April 28

Single cell analysis by super-resolution microscopy

Long Cai

View Abstract

We have recently demonstrated a technology using sequential hybridization and single
molecule FISH to multiplex a large number of mRNA molecules directly in single cells in
complex tissue samples. mRNAs in cells are barcoded by sequential rounds of hybridization,
imaging, and probe stripping. The number of barcodes available with this approach scales as
F^N, where F is the number of distinct fluorophores and N is the number of hybridization rounds.
We call this method seqFISH and it is conceptually akin to “sequencing” mRNAs directly in cells
by FISH.