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Colloquium

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April 30, 2015

May 7th Colloquium

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Speaker: Hailin Wang, University of Oregon

Title: Communicating Between Disparate Quantum Systems via Radiation Pressure Force

Abstract:

It is well known that radiation pressure force of light can be used for the manipulation of mechanical motion in microscopic systems. Notable examples include laser cooling and laser tweezers.   In this talk, I will discuss recent experimental advances on the use of radiation pressure force to control mechanical motion in macroscopic systems, with a focus on potential applications in quantum networks. Experimental studies on storing light as a mechanical excitation and on converting coherent optical fields between vastly different optical wavelengths via radiation pressure forces will be highlighted. Special physical processes that can exploit mechanical interactions while avoiding effects of thermal mechanical noise will also be discussed.

Host: Eric Corwin, Dietrich Belitz

April 27, 2015

April 30th Colloquium

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Speaker: Tommaso Baldacchini, Newport Corporation
Title: Making and Characterizing Small Things

Abstract:

Two-photon polymerization (TPP) is an enabling technology that allows fast prototyping of parts with feature sizes smaller than 100 nm. Due to its ability to fabricate microstructures with arbitrary three-dimensional geometries, TPP has been employed in diverse fields such as photonics, microelectronics, microelectromechanical systems, microfluidics, and bioengineering. However, no information is available to date that microscopically correlates the experimental conditions used in TPP with the properties of the ultimate microstructure. A study is presented where the distribution of polymer cross-linking in three-dimensional microstructures fabricated by TPP is visualized by means of nonlinear microscopy. In particular, coherent anti-Stokes Raman scattering (CARS) microscopy is employed to image polymer microstructures with chemical specificity. The characterization of the microstructures based on the acquired images permits rational optimization of the TPP process.

Biosketch: After studying Chemistry at the University of Rome “La Sapienza”, Tommaso Baldacchini pursued doctoral research at Boston College. Under the guidance of Professor John T. Fourkas, he worked on unconventional methods to fabricate three-dimensional microstructures and received a Ph.D. in Physical Chemistry in 2004. He then joined the research group of Professor Eric Mazur at Harvard University as a postdoctoral fellow, where his work focused on the wettability properties of micro- and nano-structured surfaces prepared by femtosecond laser ablation. In 2006 he joined the Technology and Applications Center at Newport Corporation as a Staff Scientist. His research interests lie in the applications of nonlinear optics in microscopy and nanofabrication.

Host: Bryan Boggs

April 20, 2015

April 23rd Colloquium

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Steven van Enk : University of Oregon

Detecting Errors in Quantum Computers

Abstract:

In the best quantum computing devices we have nowadays errors occur very rarely.

We do have to know what type of errors occur as only certain types can be corrected.

Unfortunately, the best quantum computing experiments employ so many qubits that we cannot possibly simulate the experiment anymore on a classical computer. So, how do we figure out whether only the right types of errors occur? After a brief introduction to quantum computing I’ll discuss a solution to this problem based on model selection and the Akaike Information Criterion.

April 10, 2015

April 16th Colloquium

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Grzegorz Szamel :

Colorado State University

Glassy Dynamics: Fundamental Differences Between Two and Three Dimensions

Abstract:

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

Abstract:

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

Abstract:

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

Abstract:

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

Abstract:

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

Abstract:

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.

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