128 research outputs found
Direct Measurement of Quantum Dot Spin Dynamics using Time-Resolved Resonance Fluorescence
We temporally resolve the resonance fluorescence from an electron spin
confined to a single self-assembled quantum dot to measure directly the spin's
optical initialization and natural relaxation timescales. Our measurements
demonstrate that spin initialization occurs on the order of microseconds in the
Faraday configuration when a laser resonantly drives the quantum dot
transition. We show that the mechanism mediating the optically induced
spin-flip changes from electron-nuclei interaction to hole-mixing interaction
at 0.6 Tesla external magnetic field. Spin relaxation measurements result in
times on the order of milliseconds and suggest that a magnetic field
dependence, due to spin-orbit coupling, is sustained all the way down to 2.2
Tesla.Comment: An additional EPAPS file in PDF format is available for download at
the publications section of our website
http://www.amop.phy.cam.ac.uk/amop-ma
Exciton mediated one phonon resonant Raman scattering from one-dimensional systems
We use the Kramers-Heisenberg approach to derive a general expression for the
resonant Raman scattering cross section from a one-dimensional (1D) system
explicitly accounting for excitonic effects. The result should prove useful for
analyzing the Raman resonance excitation profile lineshapes for a variety of 1D
systems including carbon nanotubes and semiconductor quantum wires. We apply
this formalism to a simple 1D model system to illustrate the similarities and
differences between the free electron and correlated electron-hole theories.Comment: 10 pages, 6 figure
A nanometer-scale optical electrometer
Self-assembled semiconductor quantum dots show remarkable optical and spin
coherence properties, which have lead to a concerted research effort examining
their potential as a quantum bit for quantum information science1-6. Here, we
present an alternative application for such devices, exploiting recent
achievements of charge occupation control and the spectral tunability of the
optical emission of quantum dots by electric fields7 to demonstrate
high-sensitivity electric field measurement. In contrast to existing
nanometer-scale electric field sensors, such as single electron transistors8-11
and mechanical resonators12,13, our approach relies on homodyning light
resonantly Rayleigh scattered from a quantum dot transition with the excitation
laser and phase sensitive lock-in detection. This offers both static and
transient field detection ability with high bandwidth operation and near unity
quantum efficiency. Our theoretical estimation of the static field sensitivity
for typical parameters, 0.5 V/m/ \surd Hz, compares favorably to the
theoretical limit for single electron transistor-based electrometers. The
sensitivity level of 5 V/m/ \surd Hz we report in this work, which corresponds
to 6.4 * 10-6 e/ \surd Hz at a distance of 12 nm, is worse than this
theoretical estimate, yet higher than any other result attained at 4.2 K or
higher operation temperature
Chirality dependence of the radial breathing phonon mode density in single wall carbon nanotubes
A mass and spring model is used to calculate the phonon mode dispersion for
single wall carbon nanotubes (SWNTs) of arbitrary chirality. The calculated
dispersions are used to determine the chirality dependence of the radial
breathing phonon mode (RBM) density. Van Hove singularities, usually discussed
in the context of the single particle electronic excitation spectrum, are found
in the RBM density of states with distinct qualitative differences for zig zag,
armchair and chiral SWNTs. The influence the phonon mode density has on the two
phonon resonant Raman scattering cross-section is discussed.Comment: 6 pages, 2 figures, submitted to Phys. Rev.
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