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Colloquium

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January 20, 2015

January 22 Colloquium

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Stephen Eckel, NIST

Studying Superfluidity in Cold-Atom Circuits

Abstract:

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

Abstract:

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

Abstract:

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

Abstract:

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

Abstract:

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).

References
[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

Abstract:

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

Abstract:

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

October 30 Colloquium

 

Gray Rybka, University of Washington

The Generation 2 Axion Dark Matter Experiment

Abstract:

Axions are an exceptionally well-motivated dark matter candidate in addition to being a consequence of the Peccei-Quinn solution to the strong CP problem. ADMX (Axion Dark Matter eXperiment) has recently been selected as the axion search for the US DOE Second-Generation Dark Matter Program. I will discuss the imminent upgrade of ADMX to a definitive search for micro-eV mass dark matter axions as well as the ongoing research and development of new technologies to expand the reach of ADMX to the entire plausible dark matter axion mass range.

Host: Spencer Chang

October 16, 2014

October 23 Colloquium

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Graham Kribs, University of Oregon, Physics

What’s So Super About Symmetries

Abstract:

I’ll review why exact and approximate symmetries occupy such a central role in our understanding of fundamental building blocks of the universe. New (approximate) symmetries, such as supersymmetry, may yet play a significant role in our understanding of nature. I’ll briefly highlight implications of supersymmetry, focusing on a specific model (pioneered by my collaborators and myself) that has an even further enlarged symmetry.

This model stabilizes the Higgs mass, and can (at least partially) explain why the LHC and other indirect experiments have not yet seen evidence for supersymmetry near the weak scale.

 

 

October 10, 2014

October 16 Colloquium

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Kyle Cranmer, New York University

What’s Next For the Large Hadron Collider

Abstract:

The discovery of the Higgs boson in 2012 was a huge success for the Large Hadron Collider.

So what’s next? I will discuss how the discovery of the Higgs (and nothing else) has influenced our thinking and the potential for our second run with higher energies and flux.

 

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