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April 10, 2015

April 16th Colloquium

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Grzegorz Szamel :

Colorado State University

Glassy Dynamics: Fundamental Differences Between Two and Three Dimensions


The two-dimensional freezing transition is very different from its three-dimensional counterpart. In contrast, the glass transition is usually assumed to have similar characteristics in two and three dimensions. Using computer simulations we show that glassy dynamics in supercooled two- and three-dimensional fluids are fundamentally different. Specifically, transient localization of particles upon approaching the glass transition is absent in two dimensions, whereas it is very pronounced in three dimensions. Moreover, the temperature dependence of the relaxation time of orientational correlations is decoupled from that of the translational relaxation time in two dimensions but not in three dimensions. Lastly, the relationships between the characteristic size of dynamically heterogeneous regions and the relaxation time are very different in two and three dimensions. These results strongly suggest that the glass transition in two dimensions is different than in three dimensions.

Host: Eric Corwin

April 7, 2015

April 9th Colloquium

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Yasutomo J. Uemura, Columbia University

MuSR Studies of Itinerant-Electron Magnets MnSi and (Mn,Fe)Si: First-Order Quantum Phase Evolution, Effect of Disorder, and Fluctuating Skyrmion Liquids

Abstract: MnSi is an interesting metallic magnet which orders into helical/conical/ferromagnetic spin structure below Tc = 29 K at ambient pressure with a small ordered moment of 0.4 Bohr magneton per Mn. Application of hydrostatic pressure of 16 kbar drives this system to be paramagnetic at T = 0. (Mn,Fe) substitution also suppresses magnetic order, yet with the additional effect of randomness, Several years ago, “Skyrmion” spin correlation was discovered in a small region near Tc in applied external field in bulk MnSi and (Mn,Fe)Si, and a larger region of B-T phase diagram in thin films of these systems.

We have performed Muon Spin Relaxation (MuSR) measurements on these systems at TRIUMF (Vancouver) and PSI (Zurich). MuSR results revealed: (1) in a bulk single crystal of MnSi, first order phase transition, with phase separation between magnetically ordered and paramagnetic regions, appears near the phase boundary to paramagnetic state, associated with suppression of dynamic critical behavior; (2) in a bulk single crystal of (Mn,Fe)Si with applied pressure, features for second order quantum evolution is recovered, revealing hidden quantum critical point for pure MnSi; (3) Skyrmion region has reduced order parameter and enhanced dynamic muon spin relaxation rate in MnSi and (Mn,Fe)Si; (4) dynamic critical behavior is gradually suppressed by the applied field in these systems, and (5) dynamic critical behavior is completely absent between the static Skyrmion lattice and fluctuating Skyrmion liquid regions in a thin film of MnSi with 50 nm thickness. These results will be compared with theories of Belitz and collaborators for itinerant magnets and of Nagaosa for Skyrmion spin systems.


March 23, 2015

April 2 Colloquium

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Manoj Kanskar, nLight

High Power Lasers – Industry Perspective


Diode lasers in the near infra-red have improved in power, efficiency, reliability and cost over the past several decades. As a result lasers have transformed from being scientific instruments to tools pervasively used in manufacturing cars, planes, ships, industrial equipment, electronics, hand-held mobile devices and touch-screens and large displays. Part of this revolution is due to the advent of fiber lasers which are impressive brightness converters producing multiple kilowatts of average power and hundreds of kilowatt of peak power. The critical technological advancements that have enabled the rise of high power diode and fiber lasers to their current state will be briefly reviewed. Further power-scaling in fiber lasers is currently limited by nonlinear effects such as stimulated Brillouin scattering (SBS), stimulated Rayleigh scattering (SRS) and the recently-identified roadblock – modal instability. Included in the talk will be discussion of ongoing work to solve these issues using Chirally-coupled Core (CCC) fiber. Chiral architecture results in interaction between CCC fiber modes involving both spin and orbital angular momentum of the waves. This enables a new degree of freedom for controlling fiber modal properties.


March 9, 2015

March 12 Colloquium

Jen Dionne, Stanford University

Mind the Gap: Quantum Effects and Optical-frequency Magnetism in Plasmonic Particle Junctions


Electrons and photons can coexist as a single entity called a surface plasmon—an elementary excitation found at the interface between a conductor and an insulator. Plasmons are evident in the vivid hues of rose windows, which derive their color from small metallic nanoparticles embedded in the glass. They also provide the basis for color-changing biosensors, photo-thermal cancer treatments, improved photovoltaic cell efficiencies, and nano-optical tweezers. While most applications have relied on classical plasmonic effects, quantum phenomena can also strongly influence the plasmonic properties of nanometer-scale systems. In this presentation, I’ll describe my group’s efforts to probe plasmon modes spanning both classical and quantum domains. We first explore the optical resonances of individual metallic nanoparticles as they transition from a classical to a quantum-influenced regime. We then use these results to monitor heterogeneous catalytic reactions on individual nanoparticles. Subsequently, using real-time manipulation of plasmonic particles, we investigate plasmonic coupling between pairs of particles separated by nanometer- and Angstrom-scale gaps. For sufficiently small separations, we observe the effects of classical coupling and quantum tunneling between metallic particles on their plasmon resonances. By utilizing these effects, we demonstrate the colloidal synthesis of an isotropic metafluid or “metamaterial paint” that exhibits a strong magnetic response – and the potential for negative refractive indices – at visible frequencies. Finally, we introduce a new technique, cathodoluminescence tomography, that enables three-dimensional visualization of light-matter interactions with nanoscale spatial and spectral resolution.

March 2, 2015

March 5 Colloquium

Terry Takahashi, UO Institute of Neuroscience

Why We Don’t Hear Echoes: An Analysis of Acoustics and Neurophysiology


A common experience to anyone that has recorded a lecture, is the “boomy” or hollow quality of the recording that can make speech comprehension difficult. This differs markedly from our experience when we are actually sitting in the lecture hall. The boomy quality is due to the acoustical reflections from nearby surfaces that add at our eardrums to the sound waves arriving directly from the lecturer. Why don’t we hear these echoes? This question, first reported in 1846, was brought into the laboratory in 1948 and has been investigated since. The broadly accepted reason is that the sound arriving directly from the lecturer arrives a few milliseconds before the echo and triggers a suppressive mechanism in the auditory system that preempts the neural responses to the echo. This phenomenon has been called the “precedence effect”. Neuroscientists in the field have been investigating the nature of this suppression. I will present evidence from studies in the barn owl (Tyto alba), arguing that no such suppression is necessary. The precedence effect can instead be explained by the relative timing of envelope features and the simple, ubiquitous tendency of auditory neurons to respond to rising sound envelopes. This simple explanation is applicable to mammals, including humans, and can be generalized to the so-called “cocktail party effect” where a sound of interest can be occluded by independent sources of background noises.

February 25, 2015

February 26 Colloquium

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Brian Smith, University of Oxford

Generation, Manipulation and Measurement of Quantum Light: From Quantum Physics to Technology


The abilities to accurately create, manipulate and characterize quantum systems are essential for fundamental tests of quantum physics and realization of emergent quantum-enhanced technologies. Optical quantum systems offer unique capabilities in their low decoherence rates at room temperature and relative ease of control, making them ideally suited as proving grounds of quantum applications and foundations. However, a key challenge is associated with photon-photon interaction. Here I focus on our recent work to experimentally realize generation, control and measurement of non-classical states of light and their effective interaction. In particular, emphasis is placed on generation of photon-number states and coherent manipulation of quantum superpositions of photon-number states. Experimental probing of the implemented quantum operation is performed using custom detection that shows the effective nonlinear interaction can be achieved by multi-photon interference and projective measurement, but that the efficacy of this process is limited primarily by current detection techniques. Future directions of research associated with alternative measurements and resource states are discussed as potential extensions of this work.

February 20, 2015

Monday, February 23 Colloquium

Laura Sinclair, NIST

Moving the Frequency Comb out of the Metrology Lab


Frequency combs can support a dizzying array of precision measurement applications. However, until recently, high-performance combs have been limited to the well-controlled optical laboratory limiting them from reaching their full potential. I will present our development of a robust optically coherent all-pm-fiber frequency comb. In addition, I will discuss the use of combs for high-accuracy time-transfer and precision molecular spectroscopy and the implications of a robust comb for these applications.

February 17, 2015

February 17 Colloquium

Michael Raymer, UO, Philip H. Knight Professor of Liberal Arts and Science

The Bell Inequalities, the Experiments that Violate them, and the Failure of Local Realism


Einstein was wrong. That’s not a phrase we can say often, and in the case at hand he was wrong for all the right reasons – he stubbornly refused to accept what Niels Bohr claimed without any proof – that we can’t think of the properties and behaviors of quantum objects as reflecting any kind of local reality, suitably defined. In the past decades, however, experiments have been carried out showing that Einstein’s view – an essentially classical view – is untenable. It is the nature of quantum-state entanglement across large distances that precludes any kind of local, realistic theory, or local, realistic interpretation of quantum theory.

This lecture is presented without any quantum mechanics theory, and is suitable for undergraduate science majors, graduate students, and faculty who would like to see a light-hearted review and proof of the Bell Inequalities – those famous relations that brought philosophical musings into the experimental laboratory.

February 12, 2015

Monday, February 16 Colloquium- CANCELLED

Alexander Sushkov, Harvard University

Magnetic Resonance with Single Nuclear- Spin Sensitivity


Our method of nanoscale magnetic sensing and imaging makes use of nitrogen-vacancy (NV) color centers a few nanometers below the surface of a diamond crystal. Using individual NV centers, we perform NMR experiments on single protein molecules, labeled with carbon-13 and deuterium isotopes. In order to achieve single nuclear-spin sensitivity, we use isolated electronic-spin quantum bits (qubits), that are present on the diamond surface, as magnetic resonance “reporters”. Their quantum state is coherently manipulated and measured optically via a proximal NV center. This system is used for sensing, coherent coupling, and imaging of individual proton spins on the diamond surface with angstrom resolution, under ambient conditions at room temperature. Our approach may enable magnetic structural imaging of individual complex molecules, and realizes a new platform for probing novel materials, and manipulation of interacting spin systems.

February 9, 2015

Wednesday, February 11 Colloquium

Dr. William Phillips, Nobel Laureate, NIST

Spining Atoms with Light: A New Twist on Atom Optics


At the beginning of the 20th century, Einstein published three revolutionary ideas that changed forever how we view Nature. At the beginning of the 21st century, Einstein’s thinking is shaping one of the key scientific and technological wonders of contemporary life: atomic clocks, the best timekeepers ever made. Such super-accurate clocks are essential to industry, commerce, and science; they are the heart of the Global Positioning System (GPS). Today, atomic clocks are still being improved, using Einstein’s ideas to cool the atoms to incredibly low temperatures. Atomic gases reach temperatures less than a billionth of a degree above Absolute Zero, without solidifying. Such atoms enable scientists to make clocks that are accurate to better than a second in 80  million years, as well as to test some of Einstein’s strangest predictions.

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