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This Week at Physics

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Events on Thursday, February 27th, 2014

R. G. Herb Condensed Matter Seminar
Topological phases, Majorana fermions and disorder in superconductors
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Smitha Vishveshwara , University of Illinois at Urbana-Champaign
Abstract: In the hunt for Majorana particles, originally proposed in the context of particle physics, recent explorations have led to exciting prospects in superconducting wires, including potential experimental detection. Here, an introduction to topological properties of superconductors that result in Majorana modes will first be presented. It will then be argued that superconducting wires subject to various potential landscapes can exhibit rich topological behavior. As an example, it will be shown that the presence of quasiperiodic potentials can give rise to beautiful phase diagrams that mimic complex Hofstadter butterfly patterns. Finally, connections to localization physics will be made in the context of disordered topological superconductors.
Host: Perkins
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Atomic Physics Seminar
Coherent control of strongly interacting Rydberg gases in thermal vapor cells
Time: 2:00 pm
Place: 5310 Chamberlin Hall
Speaker: Prof. Tilman Pfau, University of Stuttgart
Abstract: Rydberg atoms are of great interest due to their prospects in quantum information processing. Coherent control of the strong Rydberg-Rydberg interaction allows for the realization of quantum operations and devices such as quantum gates and single-photon sources. To date, impressive experimental progress has been limited to the ultracold domain [1]. Being able to exploit this interaction in a coherent manner in thermal vapor would eliminate the need for cooling and trapping of atoms and thus offer new prospects for applications in terms of integration and scalability.&lt;br&gt;<br>
We present our progress on the coherent control and investigation of Rydberg atoms in small vapor cells. We show that we are able to drive Rabi oscillations on the nanosecond timescale to a Rydberg state by using a pulsed laser excitation and are therefore faster than the coherence time limitation given by the Doppler width [2].&lt;br&gt;<br>
A systematic investigation of the dephasing of these oscillations for different atomic densities and Rydberg S-states (n = 22-40) reveals a clear signature for Rydberg-Rydberg interaction which is the basis for quantum devices based on the Rydberg blockade. Due to the high excitation bandwidth we are probing interaction level shifts up to a few GHz which correspond to very small interatomic distances (&amp;lt; 1μm). Despite the complicated level structure for Rydberg molecular states at these distances we find that the scaling with principle quantum number is still consistent with van der Waals type interaction. The strength of the interaction exceeds the energy scale of thermal motion (i.e. the Doppler broadening) and therefore enables strong quantum correlations above room temperature [3].&lt;br&gt;<br>
Furthermore we present our latest results on the combination of the pulsed Rydberg excitation with a four-wave-mixing scheme [4] and our progress towards the creation of non-classical light. &lt;br&gt;<br>
[1] M. Saffman et al., RMP 82, 2313 (2010) and references therein &lt;br&gt;<br>
[2] B. Huber et al., PRL 107, 243001 (2011) &lt;br&gt;<br>
[3] T. Baluktsian et al., PRL 110, 123001 (2013)&lt;br&gt;<br>
[4] M. Saffman and T. G. Walker, Phys. Rev. A 66, 065403 (2002), M. M. Müller, et al. Phys. Rev. A 87, 053412 (2013)&lt;br&gt;<br>
Host: Saffman
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Astronomy Colloquium
"Scaling Computational Astrophysics"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Matthew Turk, Columbia University
Abstract: The term "Big Data" means different things to different people; often it's used to describe unstructured or semi-structured records, or fast-moving data that has to be processed quickly to be of any use, or just a huge volume of data that stretches the limits of many computing systems. In this talk, I will present how simulation and analysis have attempted to respond to the challenges of "big data" not as a goal in and of itself, but as a by-product of trying to use increasingly rich simulation data to study complex physical processes.
I will describe new avenues in understanding how the first stars in the universe formed, the simulation platform Enzo (enzo-project.org)that enables us to study these objects, and where furthering our understanding requires advancing the state of the art in hydrodynamic studies. I will present the analysis and visualization platform yt(yt-project.org), and its aim to provide a lingua franca for astrophysical phenomena, empowering individuals to ask complex and detailed questions of data. Finally, I will discuss the communities that have grown around these platforms, how retaining a focus on self-directed scientific inquiry has allowed collaboration to flourish between researchers, and why collaboration and community is the next great scaling challenge for computational astrophysics.
Host: Prof Richard Townsend
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