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Colloquium

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July 9, 2015

Colloquium Series will resume Fall 2015

Please be advised that the UO Physics Department Colloquium Series will resume Fall 2015. Colloquium coordinators for 2015-16 are Jim Brau (Fall), Dietrich Belitz (Winter), Eric Corwin (Spring)

June 1, 2015

June 4th Colloquium

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Speaker: Michael Dickey, North Carolina State University

Title: Soft, Stretchable, and Reconfigurable Materials for Electronics and Actuators

Abstract:

This talk will describe efforts in our research group to control the shape and function of soft materials (liquid metals, polymers and hydrogels) for applications that include stretchable electronics, soft robots, and self-folding polymer sheets. The research harnesses interfacial phenomena, micro fabrication, patterning, and thin films. The talk with discuss the underlying fundamental science motivating active areas of research in our group, which include:
• Ultra-stretchable wires, sensors, antennas, and microelectrodes composed of liquid metal alloys based on gallium. The metal is a liquid at room-temperature with low-viscosity (water-like) and can be micromolded due to a thin, oxide skin that forms rapidly on its surface. The metal can be patterned in a number of ways including injection into microchannels or by direct-write 3D printing. Recently, we discovered that the oxide may be the best surfactant ever reported and can be removed or deposited using electrochemistry in electrolyte as a new method to control the shape of the metal.
• Self-folding polymers sheets that change shape in response to light. These sheets are a form of shape memory polymers that are compatible with 2D patterning techniques including lithography, inkjet printing, and roll to roll processing. The appeal of this work is converting 2D patterns into 3D shapes in a hands free manner.
• New methods for patterning ions in hydrogels. This reversible process can imprint topography in the hydrogel using modest voltages, tune its local mechanical properties to create physically-reinforcing exoskeletons, and generate stresses sufficient to actuate or fold hydrogels over large distances within seconds.

Host: Physics Graduate Students, Yasin Karim

May 22, 2015

May 28th Colloquium

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Speaker: Tommaso Calarco, University of Ulm

Title: Steering Many-Body Quantum Dynamics

Abstract:

Quantum technologies are based on the manipulation of individual degrees of freedom of quantum systems with exquisite precision. Achieving this in a real environment requires pushing to the limits the ability to control the dynamics of quantum systems of increasing complexity. Optimal control techniques are known to enable steering the dynamics of few-body systems in order to prepare a desired state or perform a desired unitary transformation. I will present a recently developed optimal control method that allows doing so for a many-body quantum system undergoing e.g. a quantum phase transition in the non-adiabatic regime. This opens the way to a range of applications, from the suppression of defects in a superfluid-Mott-insulator transition with ultra-cold atoms in an optical lattice to the achievement of various quantum gates at the quantum speed limit. I will present detailed calculations we performed for different experimental scenario, together with the corresponding results obtained by experimental groups in different fields, from cold atoms to diamond NV centers. Our control method also allows for exploring more general questions like the complexity of reversing quantum many-body dynamics, steering it back to its initial state even without the ability to revert the sign of the whole Hamiltonian. I will conclude by showing some recent results we obtained in this context, as well as further questions opened by our investigations.

Host: Steven van Enk

May 15, 2015

May 21st Colloquium

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Speaker: Sid Nagel, University of Chicago

Title: Speak, Memory!  What can a material memorize?

Abstract:

Out-of-equilibrium disordered systems may preserve a memory of external driving that can be read out at a later time.  I will present one form of memory that does this in a remarkable fashion: the system remembers multiple values from a series of training inputs yet forgets nearly all of them at long times despite their continual repetition.  However, all the memories can be preserved indefinitely if noise is added.   We have found these features in two very different systems: traveling charge-density waves and cyclically sheared non-Brownian suspensions.  Thus this type of memory appears to be generic.  Moreover, it provides a concrete example of how “plasticity” in memory can arise.

Host: Eric Corwin

 

May 11, 2015

May 14th Colloquium

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Speaker: Heidi Schellman, Oregon State University

Title: “Neutrino Nus“

Abstract:

Neutrinos are almost massless chargeless particles that only feel the weak interaction. They are hard to make (unless you have a nuclear reactor lying around) and even harder to detect. Despite these obstacles, a whole new field of neutrino studies has opened up since the definite observation of neutrino oscillations in the late 90’s. I will review a small fraction of the exciting recent results in neutrino physics and outline some of our plans for the future.

Host: Dave Soper

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.

 

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