Subject: [Ayudantes2] Coloquio Extraordinario Lunes -Dto de Fisica - FCEyN

From: Andrea Bragas <[email-masked]>
Date: Wed, 23 Nov 2005 01:03:23 -0300

COLOQUIO EXTRAORDINARIO DEL DEPARTAMENTO DE FISICA
 FCEyN – UBA
 
 Charla, cafe y masitas
 En el Aula Federman, 1er piso Pabellón I. Ciudad Universitaria

 Este lunes 28 de noviembre a las 14 hs:

"Optical Control of Charge and Spin Excitations in Quantum Dots"

Fritz Henneberger

Departamento de Física, Humboldt University, Berlin, Alemania
http://photonik.physik.hu-berlin.de/overview.htm

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RESUMEN:
The control of quantum states is a key prerequisite in quantum information 
processing. The flexible spectral and time structure of light makes optical 
techniques particularly interesting. When aiming at practical applications, 
semiconductors play a major role. Here, a critical issue is decoherence that 
destroys the unitary quantum evolution. Recently, quantum dots, where the 
coupling of the electronic excitations to the semiconductor environment is 
strongly suppressed, have attracted considerable attention.

In this talk, I summarize recent work on CdSe/ZnSe quantum dot 
heterostructures grown by molecular beam epitaxy. The large Coulomb energies 
make these nanostructures very well suited candidates to study and to 
implement optical concepts of quantum control. Measurements with high spatial 
resolution allow to access single quantum dots and to study and manipulate 
individual charge and spin excitations.

Making use of the exciton fine structure, a quantum superposition is prepared. 
Distinct beats in the emission demonstrate that the decoherence times are 
longer than the radiative life-time of the exciton. The biexciton is an 
entangled state of two excitons. Direct coherent control of the biexciton is 
achieved by using resonant two-photon excitation with a pair of phase-
correlated ultra-short pulses. On the other hand, by stimulating the biexciton-
exciton transition with a subsequent pulse, the biexciton can be disentangled 
in a controlled way.
 
By appropriate doping, a resident electron can be added to the quantum dot. 
The trion, representing the fundamental optical excitation of these dots, is 
utilized to study and to manipulate single spin states. Very long spin life-
times up to 100 µs are observed. Distinct signatures are found for the 
hyperfine interaction between the electron spin and the nuclear moments of the 
lattice atoms. 

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 Estan todos invitados.
   
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 SE RUEGA PUNTUALIDAD!!
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El programa con los coloquios futuros se puede consultar en 
 www.df.uba.ar.
 
 Dudas y sugerencias: [email-masked]   [email-masked]