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Events on Monday, April 23rd, 2012

ECE 600 Seminar: Silicon Nanomembrane based Photonic Crystal Nanostructures for On-chip Open Sensor Systems
Time: 3:30 pm
Place: Engineering Hall, Room 1800
Speaker: Prof. Ray Chen, University of Texas-Austin
Abstract: We experimentally demonstrate a myriad of devices on the silicon nanmomembrane based photonic crystal platforms for chip-integrated optical absorption spectroscopy and chip-integrated biomolecular microarray assays. Infrared optical absorption spectroscopy and biomolecular assays based on conjugate-specific binding principles represent two dominant sensing mechanisms for a wide spectrum of applications in environmental pollution sensing in air and water, chem-bio agents and explosives detection for national security, microbial contamination sensing in food and beverages to name a few. The easy scalability of photonic crystal devices to any wavelength ensures that the sensing principles hold across a wide electromagnetic spectrum. Silicon, the work horse of the electronics industry, is an ideal platform for the above optical sensing applications.
Host: Prof. Luke Mawst
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Condensed Matter Theory Group Seminar
Two-electron dephasing in single Si and GaAs quantum dots
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: John Gamble, UW-Madison
Abstract: We study the dephasing of two-electron states in a single quantum dot in both GaAs and Si. We investigate dephasing induced by electron-phonon coupling and by charge noise analytically for pure orbital excitations in GaAs and Si, as well as for pure valley excitations in Si. In GaAs, polar optical phonons give rise to the most important contribution, leading to GHz dephasing rates. For Si, intervalley optical phonons lead to typical dephasing rates of ~100 kHz for orbital excitations and ~1 MHz for valley excitations. For harmonic, disorder-free quantum dots, charge noise is highly suppressed for both orbital and valley excitations, since neither has an appreciable dipole moment to couple to electric field variations from charge fluctuators. However, both anharmonicity and disorder break the symmetry of the system, which can lead to increased dipole moments and therefore faster dephasing rates.
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