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This Week at Physics

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Events on Thursday, December 11th, 2014

R. G. Herb Condensed Matter Seminar
Probing the Materials Origins of Decoherence in Superconducting Qubits
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Dr. Vincenzo Lordi, Lawrence Livermore Lab
Abstract: The practicality of superconducting qubits for scalable quantum computing applications is limited by decoherence noise that reduces the useful lifetime of the quantum states. While various theories explain possible mechanisms for the decoherence, the microscopic origins at the level of the materials comprising actual devices remain largely unknown. Such knowledge is essential to enabling rational improvement of fabrication processes for higher performing qubits. First-principles simulations at the atomic level provide a useful tool to probe the materials origins of decoherence. Here, we discuss recent work investigating magnetic fluctuators associated with materials defects that can contribute decoherence noise in these systems. In particular, native defects and adsorbates on the surface of sapphire and dangling bond defects on the surface of amorphous silica will be discussed. In addition, interactions among spins on surfaces can be important, and we present detailed calculations on the energetics of such interactions. We find that the spin-spin coupling strength can be strongly influenced by lattice strain and the presence of defects. Finally, an analysis of the correlations between local structural and electronic properties of amorphous materials will be presented in this context.
Host: McDermott
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
A preview of the Planck 2014 cosmology
Time: 2:30 pm
Place: 4272 Chamberlin Hall
Speaker: Ben Wandelt, Institut Astrophysique de Paris
Abstract:
The cosmic microwave background (CMB) carries a cosmic message, preserved through time, written in its anisotropies. The Planck mission is now about to reveal a new chapter of this message using high-resolution nearly all-sky information of the polarization anisotropies for the first time, in addition to upgrading from the nominal mission to the full mission data set. These data provide new insights into several open questions related to the nature of the primordial fluctuations that seeded all structure; the global properties of the universe; neutrinos; dark matter; dark energy; atomic physics; and gravity.
Host: Peter Timbie
Poster: http://www.physics.wisc.edu/twap/posters/2014/3424.pdf
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Astronomy Colloquium
The Cosmological Context of Star Formation
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Tom Quinn, University of Washington
Abstract: On the molecular cloud scale, star formation is a very complicated
process that involves gravitational collapse, radiative transfer and magnetic fields on sub-parsec scales. On the other hand, there are a number of observed relationships between star formation and galactic and cosmic environment such as star formation rate - molecular surface density relationship in disk galaxies, the stellar mass - halo mass relationship, and the evolution of the star formation rate over time.
Modeling these relationships therefore requires simulations of
enormous dynamic range and well motivated prescriptions for the star formation physics that is still unresolved. Here, I will describe techniques for capturing this dynamic range, and models for star formation and its interaction with the interstellar medium. I will also describe recent successes in understanding star formation histories as function galactic size, merger history and cosmic time.
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