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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.

February 2, 2015

February 5 Colloquium

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Carl Wieman, Nobel Laureate, Stanford University

Expertise in Physics and How it is Best Learned and Taught


I will discuss how research has illuminated what it means to “think like an expert” (i.e. have expertise), and how those abilities are developed. I will move from cognitive psychology studies of expertise in general to the specific elements of physics expertise and research on both measuring and teaching physics expertise at a variety of levels. This will elucidate the essential roles in the learning process of both content expertise of the teacher and specific cognitive activities of the students; providing guiding principles for effective ways to teach physics for all levels and contexts.

January 26, 2015

January 29 Colloquium

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Esther Wertz, University of Michigan

Exciton-Polaritons and Localized Surface Plasmons: Light-Matter Interactions at Different Scales


Light interacts with matter through processes such as absorption, scattering and emission so that by monitoring the changes in these interactions we can learn about the nature of the light’s environment, and, conversely, we can use these interactions to manipulate light in new ways. In this seminar, I will discuss two systems in which I have investigated light-matter interactions. First, I will talk about exciton-polaritons, quasi-particles arising from the strong coupling between quantum well excitons and cavity photons. The bosonic nature of these particles makes them good candidates to investigate the physics of Bose condensates in a solid state system, while their mixed light-matter nature allows us to optically manipulate them. In the second part of my talk, I will discuss localized surface plasmons resonances, and how we can unravel the coupling of light to a nano-antenna through single-molecule fluorescence imaging. This technique is a powerful tool to optically study structures beyond the diffraction limit by localizing isolated fluorophores and fitting the emission profile to the microscope point-spread function. By using the random motion of single dye molecules in solution to stochastically scan the surface, and by assessing emission intensity and density of emitters as a function of position, we show that the fluorophore emission location is strongly shifted upon coupling to the antenna, and that dyes can be coupled to nano-antennas at distances up to 90 nm away, i.e., much farther than the 10-20 nm plasmon enhancement length.

January 20, 2015

January 22 Colloquium

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Stephen Eckel, NIST

Studying Superfluidity in Cold-Atom Circuits


Superfluidity, or flow without resistance, is a macroscopic quantum effect that is present in a multitude of systems, including liquid helium, superconductors, and ultra-cold atomic gases. Here, I will present our work studying superfluid flow in a Bose-Einstein condensate (BEC) of sodium atoms. By manipulating optical potentials, we are able to form BECs into any shape, including rings and targets. Ring condensates are unique in that they can support quantized, persistent currents. We drive transitions between persistent current states using a rotating perturbation, or weak link. This ring and rotating potential form a circuit, which is analogous to an rf superconducting quantum interference device (SQIUD). Our circuit shows the essential features of an rf-SQUID, including tunable transitions between quantized persistent current states and hysteresis. Such features make an rf-SQUID a sensitive magnetometer; by analogy, our device could act as a rotation sensor. In addition to these experiments, we have also realized other geometries such as a dumbbell and a dc-SQUID, that allow us to study critical velocities and resistive flow in superfluids. These, and similar experiments with tunable geometries, shed new light onto the details of quantum transport and superfluidity, and may pave the way for new ‘atomtronic’ devices.

January 9, 2015

January 15 Colloquium

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Christian Schneider, UCLA

Quantum Control of Atoms, Ions, and Nuclei


Cold atoms and ions provide an interesting playground for a variety of measurements of fundamental physics. Using RF traps, experiments become possible with both large ensembles of ions, e.g. in cold chemistry, and few/single ions, such as in quantum computations/simulations or optical clocks, where ultimate quantum control is required. In the first part of the talk, recent results from our work in cold chemistry and cold molecular ions using a hybrid atom-ion experiment will be presented. We have developed an integrated time-of-flight mass spectrometer, which allows for the analysis of the complete ion ensemble with isotopic resolution. Using this new setup, we have significantly enhanced previous studies of cold reactions in our system. Potential routes towards ultra-cold reactions at the quantum level will be presented. Current work aims at demonstrating rotational cooling of the molecular ions and photo-associating molecular ions.

The second part of the talk reports on our results of the search for the low-energy isomeric transition in thorium-229. This transition in the vacuum-ultraviolet regime (around 7.8 eV) has a lifetime of tens of minutes to several hours and is better isolated from the environment than electronic transitions. This makes it a very promising candidate for future precision experiments, such as a nuclear clock or tests of variation of fundamental constants, which could outperform implementations based on electronic transitions. Our approach of a direct search for the nuclear transition uses thorium-doped crystals and, in a first experiment, synchrotron radiation (ALS, LBNL) to drive this transition. We were able to exclude a large region of possible transition frequencies and lifetimes. Currently, we continue our efforts with enhanced sensitivity using a pulsed vuv laser system.

January 5, 2015

January 8 colloquium

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Ray Frey, UO

Prospects for Joint Observations of Gravitational Waves and Gamma-Ray Bursts


I will present the status of Advanced LIGO and the prospects for detection of gravitational waves, with particular focus on the scientific benefits for detections of gamma-ray bursts (GRB) and their astrophysical sources with both electromagnetic and gravitational radiation.

December 1, 2014

December 4 Colloquium

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Lloyd Knox, UC Davis

Probing the Big Bang with Maps of the Intensity and Polarization of the Microwave Sky


I will present the latest, still preliminary, results from the Planck satellite’s all-sky observations of intensity and polarization at millimeter to submillimeter wavelengths. I will pay special attention to implications for cosmic inflation, which is our leading candidate theory for the origin of all structure in the universe, and the cosmic neutrino background.

Host: Spencer Chang

November 21, 2014

November 20 Colloquium

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Peter Fischer, Lawrence Berkeley National Laboratory & University of California, Santa Cruz

Magnetic Soft X-­ray Spectromicroscopy: From Nanoscale Behavior to Mesoscale Phenomena


The era of nanomagnetism, which aims to understanding and controlling magnetic properties and behavior on the nanoscale, is currently expanding into the mesoscale [1]. This will harness enhanced complexity and novel functionalities, which are essential parameters to meet future challenges in terms of speed, size and energy efficiency of spin driven devices. The development and application of multidimensional visualization techniques, such as tomographic magnetic imaging and investigations of fast and ultrafast spin dynamics down to fundamental magnetic length and time scales with elemental sensitivity in emerging multi-component materials will be crucial to achieve mesoscience goals.

Magnetic soft X-ray spectromicroscopy is a unique analytical technique combining X-ray magnetic circular dichroism (X-MCD) as element specific magnetic contrast mechanism with a spatial resolution down to currently about 20nm. In addition, utilizing the inherent time structure of current synchrotron sources fast magnetization dynamics in ferromagnetic elements can be performed with a stroboscopic pump-probe scheme with 70ps time resolution [2, 3]. I will review in this talk recent achievements with full-field magnetic soft x-ray transmission microscopy (MTXM) with examples from magnetic vortex structures [4] and their application to novel magnetic logic elements [5], magnetic spectromicroscopy of domain walls [6], and first attempts to image the 3dim magnetic domain structures in rolled-up Ni nanotubes [7].

This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy under Contract No. DE-AC02-05-CH1123 and by the Leading Foreign Research Institute Recruitment Program (Grant No. 2012K1A4A3053565) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (MEST).

[1] R. Service, Science 335 1167 (2012)
[2] P. Fischer, Materials Science & Engineeering R72 81-95 (2011)
[3] W. Chao, et al., Optics Express 20(9) 9777 (2012)
[4] M.-Y. Im, et al., Nature Communications 3 983 (2012)
[5] H. Jung, et al., Scientific Reports 1 59 (2011)
[6] M.J. Robertson, et al., JAP (2014) under review
[7] R. Streubel, Adv. Mater 26 316 (2014)

Host: Ben McMorran

November 13 Colloquium

Itay Yavin, McMaster University & Perimeter Institute for Theoretical Physics

Dark Matter as a Fundamental Particle


In this talk I will review past and present ideas about dark matter as a new fundamental particle, exploring both the underlying theoretical structures as well as the variety of experimental frontiers. Along the way I will try to give you a flavor of some of the most recent developments as well as future plans and prospects.

Host: Spencer Chang

November 6 Colloquium

Tracy Slatyer, Massachusetts Institute of Technology

A Potential Dark Matter Signal in Light from the Central Milky Way


Dark matter comprises five-sixths of the matter in the universe, and is one of the strongest pieces of evidence for new physics beyond the Standard Model. To date, dark matter has only been detected via its gravitational interactions, but its annihilation or decay could produce high-energy particles observable by Earth-based telescopes. In this talk, I will describe an unexplained glow of gamma rays observed from the inner regions of the Milky Way, and discuss its possible origins, including the exciting possibility that it might arise from dark matter annihilation.

Host: Spencer Chang

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