1,141 research outputs found
Anisotropic Curvature Flow of Immersed Networks
We consider motion by anisotropic curvature of a network of three curves immersed in the plane meeting at a triple junction and with the other ends fixed. We show existence, uniqueness and regularity of a maximal geometric solution and we prove that, if the maximal time is finite, then either the length of one of the curves goes to zero or the L2-norm of the anisotropic curvature blows up
Voltage-controlled electron-hole interaction in a single quantum dot
The ground state of neutral and negatively charged excitons confined to a
single self-assembled InGaAs quantum dot is probed in a direct absorption
experiment by high resolution laser spectroscopy. We show how the anisotropic
electron-hole exchange interaction depends on the exciton charge and
demonstrate how the interaction can be switched on and off with a small dc
voltage. Furthermore, we report polarization sensitive analysis of the
excitonic interband transition in a single quantum dot as a function of charge
with and without magnetic field.Comment: Conference Proceedings, Physics and Applications of Spin-Related
Phenomena in Semiconductors, Santa Barbara (CA), 2004. 4 pages, 4 figures;
content as publishe
Voltage-Controlled Optics of a Quantum Dot
We show how the optical properties of a single semiconductor quantum dot can
be controlled with a small dc voltage applied to a gate electrode. We find that
the transmission spectrum of the neutral exciton exhibits two narrow lines with
eV linewidth. The splitting into two linearly polarized
components arises through an exchange interaction within the exciton. The
exchange interaction can be turned off by choosing a gate voltage where the dot
is occupied with an additional electron. Saturation spectroscopy demonstrates
that the neutral exciton behaves as a two-level system. Our experiments show
that the remaining problem for manipulating excitonic quantum states in this
system is spectral fluctuation on a eV energy scale.Comment: 4 pages, 4 figures; content as publishe
Optical detection of single electron spin resonance in a quantum dot
We demonstrate optically detected spin resonance of a single electron
confined to a self-assembled quantum dot. The dot is rendered dark by resonant
optical pumping of the spin with a coherent laser. Contrast is restored by
applying a radio frequency (rf) magnetic field at the spin resonance. The
scheme is sensitive even to rf fields of just a few micro-T. In one case, the
spin resonance behaves exactly as a driven 3-level quantum system (a
lambda-system) with weak damping. In another, the dot exhibits remarkably
strong (67% signal recovery) and narrow (0.34 MHz) spin resonances with
fluctuating resonant positions, evidence of unusual dynamic processes of
non-Markovian character.Comment: 4 pages, 5 figure
Absorption and photoluminescence spectroscopy on a single self-assembled charge-tunable quantum dot
We have performed detailed photoluminescence (PL) and absorption spectroscopy
on the same single self-assembled quantum dot in a charge-tunable device. The
transition from neutral to charged exciton in the PL occurs at a more negative
voltage than the corresponding transition in absorption. We have developed a
model of the Coulomb blockade to account for this observation. At large
negative bias, the absorption broadens as a result of electron and hole
tunneling. We observe resonant features in this regime whenever the quantum dot
hole level is resonant with two-dimensional hole states located at the capping
layer-blocking barrier interface in our structure.Comment: 6 pages, 6 figure
Dynamic nuclear spin polarization in resonant laser spectroscopy of a quantum dot
Resonant optical excitation of lowest-energy excitonic transitions in
self-assembled quantum dots lead to nuclear spin polarization that is
qualitatively different from the well known optical orientation phenomena. By
carrying out a comprehensive set of experiments, we demonstrate that nuclear
spin polarization manifests itself in quantum dots subjected to finite external
magnetic field as locking of the higher energy Zeeman transition to the driving
laser field, as well as the avoidance of the resonance condition for the lower
energy Zeeman branch. We interpret our findings on the basis of dynamic nuclear
spin polarization originating from non-collinear hyperfine interaction and find
an excellent agreement between the experimental results and the theoretical
model
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