Events Archive

Feb
17
2015
Collective Motion of Interacting Random Walkers
The collective motion of a large group of individuals has two different scales. Individuals move and interact on a local scale, while the motion of the group as a whole occurs on a global scale. All the movement of the group on the global scale is produced by the many movements of its members, and so a good model for the global behaviour should arise from local models for the individuals. We investigate the link between the two scales, and create formulae for producing a global model for any particular lattice-based local model using mean-field approximations.
Feb
16
2015
Magnetism, Rotons, and Beyond: Engineering Atomic Systems with Lattice Shaking
Conventional methods of quantum simulation rely on kinectic energy determined by free particle dispersions or simple sinusoidal optical lattices. Solid state systems, by contrast, exhibit a plethora of band structures which differ quantitatively, qualitatively, and even topologically....
Feb
12
2015
Magnetic Structure Solution of Frustrated Spin Systems
In frustrated magnetic materials, geometry and magnetic interactions combine to suppress conventional magnetic order. Instead, disordered "spin liquid" states can host exotic magnetic phenomena which persist to the lowest measurable temperatures. Neutron scattering is an ideal experimental technique to understand spin-liquid states, but the absence of conventional magnetic order means that standard data-analysis methods cannot be used. Two limitations have traditionally restricted our understanding spin liquids at the atomic scale: (i) the magnetic interactions must be anticipated, and (ii) single-crystal samples must be available....
Feb
09
2015
How Many Angels Can Dance on the Head of a Black Hole
I will try to explain, in elementary terms, the deep connection between space-time geometry and quantum entropy, uncovered in the work of Bekenstein, Hawking, 't Hooft, Gibbons Jacobson, Fischler, Susskind and Bousso. This leads to the conclusion that many of the fundamental degrees of freedom, which describe our world, are inaccessible to direct local measurement. Indeed, local excitations are constrained low entropy states of the fundamental degrees of freedom. These insights give us clues to the nature of a fundamental theory of quantum gravity, and have implications for early universe...
Feb
05
2015
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 on cold chemistry and cold molecular ions using a hybrid atom--ion experiment will be...
Jan
29
2015
Deciphering the blips, bumps and whirls of the gravitational universe
The dawn of gravitational wave astronomy is upon us as Advanced LIGO and Advanced Virgo begin to come on line later this year. With the first detection of gravitational waves, the cosmic cacophony of the gravitational universe will be open to us, allowing us to probe some of the densest regions in the universe as well as some of the most energetic astronomical phenomena (eg. gamma-ray bursts). In order to perform gravitational wave astronomy, one must decipher the astrophysical information encoded in the detected gravitational wave signals. This seminar will give a brief overview of the...
Jan
27
2015
Hydrodynamics and Collective Behavior of Tethered Microbes
Microbial ecosystems in the top decimeters of sediment play an important role in determining the chemistry of the atmosphere and help support multicellular life. The metabolic rates of these microbes are strongly limited by the time it takes nutrients to diffuse from the surface. Here we combine experiments, mathematical models, and field work to understand how two microbes, the bacteria Thiovulum majus and the eukaryote Uronemella, respond collectively to overcome diffusion limitation. These microbes have independently evolved the ability attach to surfaces by means of a mucus tether. Once...
Jan
26
2015
Using Clock Precision to Study Manybody Physics
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Jan
15
2015
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 ^{13}C and ^2H isotopes. In order to achieve single nuclear-spin sensitivity, we...
Dec
11
2014
Galaxy clusters: laboratories for extreme plasma physics
Galaxy clusters are the most massive virialized objects in the universe, and have the potential to be highly accurate probes of cosmological parameters. A fundamental challenge for cluster cosmology is to estimate the masses of these objects using observational proxies such as X-ray luminosity and temperature, which are complicated by the merger history of clusters and the microphysical properties of the intracluster medium. These effects, while frustrating to cosmologists, provide a rich laboratory for exploring the plasma physical processes that are occurring in these massive objects. In this talk I will...

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