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This Week at Physics

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Events During the Week of March 9th through March 16th, 2014

Monday, March 10th, 2014

Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
Time: 12:00 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:
Please feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Le Zhang (lzhang263@wisc.edu)
Host: Peter Timbie
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Faculty Candidate Seminar
How, when and where in pattern formation: Spying on embryonic development one molecule at a time
Time: 4:00 pm
Place: Chamberlin Hall 4274
Speaker: Hernan Garcia, Princeton
Abstract: An abiding mystery in the study of living matter is how a single cell develops into a multicellular organism. As this cell divides, its progeny read the program encoded on their DNA and adopt different fates becoming familiar cell types such as those found in muscle, liver and our brains. We now know that the decisions that cells make during development are not so much based on which genes to express, but rather on when, where and how to express them. Despite advances in determining the identities of the molecules that mediate these decisions we are still incapable of predicting how simple physical parameters such as the number, position and affinity of binding sites for these molecules on the DNA determine developmental fates. Using the fruit fly, one of the classic model systems for embryonic development, I will show how a combination of new technologies, quantitative experiments, and statistical mechanics is providing new insights about cellular decision making during development. In particular, I will describe how the specification of macroscopic body parts in an organism is linked to the non-equilibrium molecular-scale processes inside single cells. The goal of this interdisciplinary research is to produce a predictive understanding of developmental programs which will enable the rational control of biological size, shape and function.
Host: Gilbert/Coppersmith
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Tuesday, March 11th, 2014

Chaos & Complex Systems Seminar
Variability, uncertainty, and vulnerability in our chaotic climate
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: John Young, UW Department of Atmospheric and Oceanic Sciences
Abstract: Climate and weather are part of a chaotic continuum which impact our world through variability, predictive and statistical uncertainty, and damaging extremes. In this talk I will illustrate these issues with examples from observed atmospheric temperature and precipitation patterns and time behavior.

Weather chaos naturally extends to slow variations and often power-law spectra. The probability distributions of temperature differ strongly from those for precipitation, which yield power law distributions at the extreme range. Impacts often result from extreme states which exceed threshold values. Since extremes are typically estimated with large uncertainty, ecological impacts are similarly estimated for a finite range of probability. An example of a physical constraint on extreme precipitation will be given: the "1,000 year flooding rain".
Host: Clint Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
X-ray Astronomy from Sounding Rockets
Time: 1:20 pm
Place: 2223 Chamberlin
Speaker: Dan McCammon, UW Madison Department of Physics
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Faculty Candidate Seminar
Photonic topological insulators and pseudomagnetism
Time: 4:00 pm
Place: 4274 Chamberlin Hall
Speaker: Mikael Rechtsman, Technion - Israel Institute of Technology,
Abstract: I will present two examples in which aEuro~fictitious fieldsaEuroTM lead to surprising photonic effects that would be difficult (if not impossible) to achieve with real fields. Firstly, I will present the first observation of the topological protection of light - a aEuro~Photonic Floquet Topological InsulatoraEuroTM [1]. The structure is an array of coupled helical waveguides (the helicity generates a fictitious circularly-polarized electric field that leads to the TI behavior). Second, I will demonstrate artificial magnetic fields (aEuro~pseudomagnetismaEuroTM) in photonic lattices [2]. The pseudomagnetic field is generated by inhomogeneously straining the system (thus breaking periodicity), and leads to photonic Landau levels with very high photonic density of states. Potential applications include robust photonic devices and strong light-matter interaction over large areas.

[1] Rechtsman, M. C. et al. Nature 496, 196aEuro"200 (2013).

[2] Rechtsman, M. C. et al. Nature Photon. 7, 153aEuro"158 (2013).
Host: Thad Walker/Sue Coppersmith
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Wednesday, March 12th, 2014

Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
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Faculty Candidate Seminar
Quantum Communications and Computation
Time: 4:00 pm
Place: 4274 Chamberlin Hall
Speaker: Graeme Smith, IBM TJ Watson Research Center
Abstract: Physical information carriers obey quantum laws. Taking proper account of this fact has led over the past few decades to profound generalizations of both communication and computation theory. I first give an overview of the quantum theory of communication, which retains many features from Shannon's classical theory but is substantially richer, involving new concepts such as entanglement, separate quantum and classical capacities, and new capabilities such as unconditionally secure cryptographic key agreement, classically impossible kinds of synergy between independent channels, and the possibility of using entangled codewords to boost classical communication rates. Next I discuss the race to build a quantum computer, and the associated problem of characterizing and certifying the "quantumness" of candidate machines. For machines large enough to be interesting, this amounts to an inference problem based on limited measurements, and also involves questions of a computational complexity. As examples, I consider how to give a legitimate implementation of ShoraEuroTMs algorithm and how to decide whether the D-wave device performs meaningful quantum computation.

Host: Thad Walker/Deniz Yavuz
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Thursday, March 13th, 2014

R. G. Herb Condensed Matter Seminar
Many body localization: a new frontier for quantum statistical physics
Time: 10:00 am
Place: 5310
Speaker: Rahul Nandkishore, Princeton University
Abstract: "The existing theory of quantum statistical mechanics describes open systems in contact with large reservoirs. However, experimental advances in the construction and control of isolated quantum systems have highlighted the need for an analogous theory of isolated systems. It has been realized that isolated quantum systems can support behavior which has no analog in open quantum systems. A prominent example is the phenomenon of many body localization.

Many body localization occurs in isolated quantum systems, usually with strong disorder, and is marked by absence of dissipation, absence of thermal equilibration, a strictly zero DC conductivity (even at energy densities corresponding to high temperatures), and a memory of the initial conditions that survives in local observables for arbitrarily long times. Recently, my co-workers and I have demonstrated that many body localization also opens the door to new states of matter which cannot exist in thermal equilibrium, such as topological order at finite energy density, or broken symmetry states below the equilibrium lower critical dimension. In this talk, I review the essential features of the many body localization phenomenon, present our recent work on localization protected order, and provide a survey of open problems. I also present my ongoing work seeking to make contact between the theory and experiments, and discuss potential technological applications of these ideas.“
Host: Chubukov
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Astronomy Colloquium
"The secret lives of Galaxy Clusters"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Brian O'shea, Michigan State University
Abstract: Galaxy clusters have the potential to be highly accurate probes of cosmological parameters. However, they are also very interesting astrophysical objects in their own right! The properties that make clusters irritating to those who wish to use them for cosmology - deviations from sphericity and hydrostatic equilibrium, shocks, mergers, and a variety of baryonic processes - provide a tremendous amount of information about these massive beasts. I will present recent efforts to understand the effects that correctly modeling the properties of gas in cosmological simulations have on the observable properties of clusters, focusing on shocks, AGN heating, and the non- thermal components of the intracluster medium, including cosmic rays and magnetic fields.
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Faculty Candidate Seminar
Quantum control of interactions between spin and photons in semiconductor quantum dot
Time: 4:00 pm
Place: 4274 Chamberlin Hall
Speaker: Wei-bo Gao, Institute of Quantum Electronics - ETH Zurich
Abstract: Optically active quantum dot represents a unique quantum system that combines solid state spin qubits with coherent optical transitions. It performs as a natural link between the study of nanoscience, atomic quantum optics and quantum information. Particularly in the frame of quantum information, my talk will focus on the optical manipulation of a quantum dot spin. Based on that, I will report the creation of entanglement between a flying photon and a semiconductor quantum dot spin, acting as a key step towards a quantum network with nodes consisting of semiconductor spin qubits. In the end, I will make a prospect and talk about where we stand in the quantum information application with optically active quantum dot.
Host: Eriksson/Coppersmith
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Friday, March 14th, 2014

Theory Seminar (High Energy/Cosmology)
Dark Matter: The Lepton Connection
Time: 2:00 pm
Place: 5280 Chamberlin Hall
Speaker: Prateek Agrawa, Fermi National Accelerator Laboratory
Abstract: I will present models where the dominant coupling of dark matter is with the Standard Model leptons, and the interactions with quarks only arise at one-loop level. These models give rise to novel phenomenology. In particular, I will show the corrections to the muon magnetic moment in the context of a set of simplified models, and compare the resulting constraints with those from direct detection and collider experiments. While these constraints are generally severe, I will highlight the limited regions of parameter space where the muon magnetic moment anomaly can be consistently explained by leptophilic dark matter.
Host: Jordi Salvadó Serra
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Physics Department Colloquium
Status and prospects for achieving thermonuclear ignition on the National Ignition Facility
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Riccardo Betti, Rochester
Abstract: Recent experiments on the National Ignition Facility (NIF) have achieved the conditions where the thermonuclear fuel is self-heated by the alpha particles produced by the fusion process. For the first time in fusion research, the self-heating process causes a significant increase of the plasma temperature ( ~ 20 - 25 % ) and a large enhancement of the fusion yield, more than doubling the number of fusion reactions. Demonstrating ignition will require much higher fusion yields and dominant self-heating by the alphas. Current NIF experiments use the indirect drive approach where a cryogenic spherical shell filled with deuterium and tritium is imploded using an x-ray drive. While these results represent an important step forward in fusion research, the path to thermonuclear ignition is uncertain. Other concepts like direct drive and shock ignition provide additional options to achieve ignition on the NIF. While all the currently available ignition options are affected by major physics uncertainties, steady progress is being made on both the NIF and OMEGA laser facilities thus improving the prospects for the achievement of ignition on NIF.
Host: Forest
Poster: http://www.physics.wisc.edu/twap/posters/2014/3194.pdf
Video: http://www.physics.wisc.edu/vod/2014/03/14.html
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2014/2014-03-10.pdf

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