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About November 2010

This page contains all entries posted to Physics Announcements in November 2010. They are listed from oldest to newest.

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November 2010 Archives

November 3, 2010

Seminar: Wednesday, November 3, 2010

No Seminar

November 5, 2010

Seminar: Friday, November 5, 2010 at 10:00 a.m

"Thermal emission from gamma-ray bursts"
Dr. Asaf Pe'er
CFA/ITC
I will discuss recent evidence for a thermal emission component that accompanies the non-thermal emission during the prompt phase of GRBs. I argue that this component is naturally explained by considering emission from the photosphere, taking into account high latitude emission from optically thick relativistically expanding plasma. The thermal flux is expected to decay at late times as F_BB ~ t^{-2}, and the observed temperature as T ~ t^{-\alpha}, with \alpha ~ 1/2 - 2/3. I will discuss some of the latest theoretical progress, including the theory of multicolor black body emission from relativistically expanding plasma. These theoretical predictions are in very good agreement with the observations. Finally, I will discuss three implications of this interpretation: (a) The relation between thermal emission and high energy, non-thermal spectra observed by FERMI, with particular emphasis on the peculiar GRB090902B. (b) The use of thermal emission to directly measure the Lorentz factor of the flow and the initial radius of the jet. (c) I argue that lack of detection of thermal component can be used to constrain the composition of GRB jets.

November 10, 2010

Seminar: Wednesday, November 10, 2010 at 3:30 p.m. Coffee 3:15 p.m.

Metal-Enhanced Fluorescence: A paradigm shift in how we think and use Fluorescence Spectroscopy today
Dr. Chris D. Geddes
Institute of Fluorescence, University of Maryland Baltimore County, Columbus Center
In recent years the IoF has described the favorable interactions and outcomes of both plasmon supporting particles (Ag, Au, Cu, Zn, Ni, Cr) and substrates with electronically excited states. These favorable effects have included significantly enhanced fluorescence emission from singlet states, S1 and S21, as well as enhanced phosphorescence yields from triplet, T1, states (MEP) 2. In addition, we have observed and described plasmon enhanced chemiluminescence intensities (MEC), as well as highly directional emission. As a result of enhanced triplet yields, we have also observed both enhanced singlet oxygen and superoxide anion yields3. These favorable influences on the photophysical properties of close proximity excited states to plasmon supporting substrates / particles has led to wealth of biochemical applications, such as the high sensitivity and ultra fast detection of proteins4, DNA5, RNA and ultra bright and photostable metal-enhanced fluorescence based particles for downstream cellular imaging applications. In addition, there are a lot downstream applications of MEP such as in photodynamic therapy by surface plasmon controlled single oxygen generation. Current thinking, describes Metal-Enhanced Fluorescence as the near-field coupling of electronic excited states to surface plasmons (a surface mirror dipole), the particle subsequently radiating the photophysical characteristics of the coupled excited state in the far-field, remarkably, even vibronic structure. In this presentation, we communicate our recent findings for metal-fluorophore interactions and our current thinking and progress towards developing a unified metal-fluorophore description.

November 19, 2010

PhD Defense - Hao You

Hao successfully defensed his dissertation on November 19, 2010.

TITLE:
Theoretical Study of Quantum Computation with Nonlinear Optics

ABSTRACT:
Quantum computing has been of intense interest over the last 10 years because of its
promising ability to do high-speed factoring and its potential for the efficient simulation
of quantum dynamics. It could be implemented in many different ways using optical
techniques. A better understanding of the advantages and disadvantages of these
approaches would allow the experimental groups working in this area to optimize their
choice of experiment and to concentrate on the approaches that are most likely to succeed.
In this thesis, we are interested in quantum logic gates based on nonlinear optical
approaches and mainly focus on one of the approaches----quantum Zeno gates. We
theoretically analyze two-photon absorption, which is essential to perform quantum Zeno
gates for coherent light and for frequency-entangled light. We also analyze and compare
quantum Zeno gates with nonlinear phase gates, which is another promising optical
implementation for quantum logic. The results of our theoretical analysis will be useful
for future experimental work in quantum computation.

PhD Defense - Yu Zhou

Yu successfully defended his PhD dissertation on November 19, 2010.

TITLE:
Multiphoton Coherence of Thermal Light

ABSTRACT:
Multiparticle interference is one of the most surprising consequences of quantum mechanics. In quantum theory, interference happens between different yet indistinguishable probability amplitudes. Probability amplitudes can be nonlocal when they are connected with systems including several particles. The interference between these nonlocal probability amplitudes sometimes can only be understood by quantum theory. In this dissertation, the multiphoton coherence of thermal light is studied, theoretically and experimentally, as the consequence of interference between nonlocal probability amplitudes. The study showed that the higher order correlation functions of thermal light had higher contrast compared with the lower order correlation functions. For example, the contrast of the Nth order correlation function of thermal light can reach N!:1. This is because in higher order correlation functions there are more cross terms from interference that contribute to the correlation peak. In this dissertation, the high contrast property is employed to increase the contrast of thermal light ghost imaging. An experiment showed that the contrast of the third order ghost image is significantly improved compared with that of the second order ghost image.

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