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This Week at Physics

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Events During the Week of August 18th through August 25th, 2019

Monday, August 19th, 2019

No events scheduled

Tuesday, August 20th, 2019

No events scheduled

Wednesday, August 21st, 2019

Theory Seminar (High Energy/Cosmology)
Quantum non-linear evolution of inflationary tensor perturbations
Time: 2:00 pm
Place: 5280 Chamberlin
Speaker: Jinn-Ouk Gong, KASI
Abstract: We study the quantum mechanical evolution of the tensor perturbations during inflation with non-linear tensor interactions. We first obtain the Lindblad terms generated by non-linear interactions by tracing out unobservable sub-horizon modes. Then we calculate explicitly the reduced density matrix for the super-horizon modes, and show that the probability of maintaining the unitarity of the squeezed state decreases in time. The decreased probability is transferred to other elements of the reduced density matrix including off-diagonal ones, so the evolution of the reduced density matrix describes the quantum-to-classical transition of the tensor perturbations. This is different from the classicality accomplished by the squeezed state, the suppression of the non-commutative effect, which is originated from the quadratic, linear interaction, and also maintains the unitarity. The quantum-to-classical transition occurs within 5 - 10 e-folds, faster than the curvature perturbation.
Host: Alex Cole
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Thursday, August 22nd, 2019

R. G. Herb Condensed Matter Seminar
Engineering Superconductivity in Semiconductor Nanowires for Quantum Device Applications
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Stephen Gill
Abstract: Semiconductor nanowires such as InAs and InSb provide a novel basis for low dimensional quantum devices. Following proposals to engineer Majorana bound states in these materials1,2, non-Abelian anyons relevant for topological quantum computing, evidence3 for such bound states was reported in highly disordered semiconductor-superconductor devices. However, the level of disorder did not preclude trivial origins to these observations and has motivated significant advances in semiconductor-superconductor devices in order to realize robust Majorana devices. In this talk, I will discuss how to engineer superconductivity in InSb nanowire devices and realize state of the art quantum transport features in hybrid semiconductor-superconductor devices. In particular, I will explain the development of epitaxial semiconductor-superconductor interfaces, which ensure uniform superconducting coupling to the nanowire and enable ballistic superconducting quantum wires to be realized in InSb. Lastly, I will discuss experiments in progress to study the transition from Andreev to Majorana bound states in ballistic InSb nanowire devices. References: 1. R. M. Lutchyn, J. D. Sau, and S. Das Sarma, Phys. Rev. Lett. 105, 077001 (2010). 2. Y. Oreg, G. Refael, and F. von Oppen, Phys. Rev. Lett. 105, 177002 (2010). 3. V. Mourik, K. Zuo, S. M. Frolov, S. R. Plissard, E. P. A. M. Bakkers, and L. P. Kouwenhoven, Science 336, 6084 (2012).
Host: Eriksson
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Cosmology Journal Club
Time: 12:00 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:
http://cmb.physics.wisc.edu/journal/index.html
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 Ross Cawthon (cawthon@wisc.edu) and Santanu Das (sdas33@wisc.edu).
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Friday, August 23rd, 2019

No events scheduled

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