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This Week at Physics

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Events on Monday, October 29th, 2012

Plasma Physics (Physics/ECE/NE 922) Seminar
No seminar
Time: 12:00 pm
Place: 1310 Sterling Hall
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Special Lunch Astronomy Talk
"Star Formation in N-Body Dwarf Galaxy Simulations"
Time: 12:00 pm
Place: 4421 Sterling Hall
Speaker: Ferah Munshi, University of Washington
Abstract: In this talk, we examine the total stellar-to-halo mass ratio as a function of halo mass for a new sample of simulated field galaxies using fully cosmological, I>CDM, high resolution SPH + N-Body simulations carried to the present time. These simulations include explicit H2 and metal cooling, star formation (SF) and supernovae (SN) driven gas outflows. We find extremely good agreement between the simulations and predictions from the statistical Halo Occupation Distribution model presented in Moster et al. (2012). This is due to a combination of systematic factors: a) gas outflows that reduce the overall SF efficiency b) estimating the stellar masses of simulated galaxies using artificial observations and photometric techniques similar to those used in observations. Our analysis provides an excellent match to previous observational estimates and suggests that stellar mass estimates based on photometric magnitudes underestimate the contribution of old stellar populations to the total stellar mass, leading to stellar mass errors of up to 50% for individual galaxies. These results highlight the importance of using proper techniques to compare simulations with observations and reduce the perceived tension between the star formation efficiency in galaxy formation models and in real galaxies.
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Condensed Matter Theory Group Seminar
Progress in Superconducting Quantum Circuits
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Robert McDermott
Abstract: Superconducting integrated circuits incorporating Josephson junctions are an attractive candidate for scalable quantum computing in the solid state. Currently, fidelity of multiqubit operations is limited by decoherence and by added noise of the qubit measurement. In this talk I describe work to improve qubit coherence and measurement fidelity. First, I describe the incorporation of crystalline silicon into phase qubit circuits; the improved qubits display energy relaxation times that are a factor 2-3 greater than those achieved with the best available amorphous materials. Next, I will describe efforts to understand and eliminate pure dephasing. We have shown that the dephasing is due to flux noise induced by surface magnetic states at the superconductor-insulator interface; in recent work we have demonstrated a fabrication process that has led to a noise suppression by more than an order of magnitude. Finally (and if time permits), I will discuss development of a novel microwave amplifier based on a variant of the dc Superconducting QUantum Interference Device (dc SQUID). With these devices we have achieved noise performance within a factor of 2 of the standard quantum limit at 8 GHz. Preliminary measurements show a significant improvement in single-shot quantum nondemolition measurement fidelity.
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