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Events on Thursday, April 10th, 2008

R. G. Herb Condensed Matter Seminar
Quantum computation using tunable flux qubits
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Matthias Steffen, IBM Yorktown Heights
Abstract: The quest towards building a practical quantum computer using superconducting materials and Josephson junctions has made rapid progress over the past several years. Experimental demonstrations ranged from high fidelity single qubit gates to elementary two-qubit gates. One major step towards continued progress consists of understanding all major sources of decoherence that destroy the fragile quantum states. In this talk we provide an overview of our experimental efforts using superconducting qubits. Our qubit is a tunable flux qubit coupled to a high quality transmission line resonator. We show quantum information storage in the resonator with lifetimes of a few microseconds. The qubit itself is shown to have short coherence times, which are not well understood at present. One possible mechanism may be due to stray capacitance of the qubit to ground and bias leads. We present a simple model of decoherence due to the stray capacitances and speculate on future design strategies.
Host: Robert McDermott
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
The role of SUSY flat directions in reheating
Time: 4:00 pm
Place: 4274 Chamberlin Hall
Speaker: Marco Peloso, University of Minnesota
Abstract: Reheating after inflation describes all the particle physics processes occurring from the decay of the inflaton up to the establishment of thermal equilibrium. Due to the strong model dependence, it is one of the most unknown stages in the history of the universe. It has been argued that SUSY flat directions are naturally excited during inflation, and that they slow down the thermalization of the inflaton decay products by providing a large effective mass to the fields they are coupled to. We discuss a nonperturbative decay channel for the flat directions which has been generally overlooked in the literature. It typically leads to a quick decay of the flat directions, and, consequently, to a suppression of their delaying effect for thermalization.
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