9 research outputs found
Engineering coherent photons from semiconductor quantum dots
Self-assembled semiconductor quantum dots (QDs) have great promise as quantum
light sources due to their ability to generate single indistinguishable photons and
entanglement. In this thesis, confocal microscopy experiments have been carried
using non-resonant photoluminescence (PL) and resonant
uorescence (RF) on QDs
with the goal of characterising and developing them into high-quality quantum light
sources.
Through the application of uniaxial strain and an electric eld, single particle
energies in a QD and their behaviour with strain are determined using a perturbative
Coulomb blockade model. The exciton energy tuning magnitude is found to be a
result of the near-cancellation of much larger single electron and hole tuning tuning.
In addition, the rate of electron con nement energy tuning with strain is found
to be correlated with the nominal unstrained con nement energy. An attempt is
made at characterising the composition of the QDs through extracting deformation
potentials, but the simple model does not capture the full system. Further, strain
tuning of the ne structure splitting (FSS) of the neutral exciton X0 from QDs
emitting at telecommunications wavelengths is shown. FSS tuning as large as 46
eV was observed, and using a phenomenological model select QDs were identi ed
to achieve FSS < 1 ueV.
RF is used to examine noise sources in QDs. Two sources of noise are considered:
electric charge noise due to a
uctuating charge environment, and nuclear spin
noise due to the hyper ne interaction of single electron spins with a large number
( ~105) of nuclear spins. While the charge noise contributes to a loss in overall
photon emission rates, but does not negatively impact the photon antibunching
or indistinguishability at low Rabi frequencies, spin noise allows inelastic Raman
scattering which reduces photon indistinguishability. The application of an external
magnetic eld in the Faraday geometry screens the electrons from the nuclear spins,
recovering a high degree of photon indistinguishability
Frequency-encoded linear cluster states with coherent Raman photons
Entangled multi-qubit states are an essential resource for quantum
information and computation. Solid-state emitters can mediate interactions
between subsequently emitted photons via their spin, thus offering a route
towards generating entangled multi-photon states. However, existing schemes
typically rely on the incoherent emission of single photons and suffer from
severe practical limitations, for self-assembled quantum dots most notably the
limited spin coherence time due to Overhauser magnetic field fluctuations. We
here propose an alternative approach of employing spin-flip Raman scattering
events of self-assembled quantum dots in Voigt geometry. We argue that weakly
driven hole spins constitute a promising platform for the practical generation
of frequency-entangled photonic cluster states
Electro-elastic tuning of single particles in individual self-assembled quantum dots
We investigate the effect of uniaxial stress on InGaAs quantum dots in a
charge tunable device. Using Coulomb blockade and photoluminescence, we observe
that significant tuning of single particle energies (~ -0.5 meV/MPa) leads to
variable tuning of exciton energies (+18 to -0.9 micro-eV/MPa) under tensile
stress. Modest tuning of the permanent dipole, Coulomb interaction and
fine-structure splitting energies is also measured. We exploit the variable
exciton response to tune multiple quantum dots on the same chip into resonance.Comment: 16 pages, 4 figures, 1 table. Final versio
Exciton fine-structure splitting of telecom-wavelength single quantum dots : Statistics and external strain tuning
In a charge tunable device, we investigate the fine structure splitting of
neutral excitons in single long-wavelength (1.1\mu m < \lambda < 1.3 \mu m)
InGaAs quantum dots as a function of external uniaxial strain. Nominal fine
structure splittings between 16 and 136 \mu eV are measured and manipulated. We
observe varied response of the splitting to the external strain, including
positive and negative tuning slopes, different tuning ranges, and linear and
parabolic dependencies, indicating that these physical parameters depend
strongly on the unique microscopic structure of the individual quantum dot. To
better understand the experimental results, we apply a phenomenological model
describing the exciton polarization and fine-structure splitting under uniaxial
strain. The model predicts that, with an increased experimental strain tuning
range, the fine-structure can be effectively canceled for select telecom
wavelength dots using uniaxial strain. These results are promising for the
generation of on-demand entangled photon pairs at telecom wavelengths.Comment: 15 pages, 3 figure
Untersuchungen zur optimalen Quantisierung und zur Stoeranfaelligkeit der zweidimensionalen Hadamard-Koeffizienten bei der Echtzeittransformation von Fernsehbildsignalen Abschlussbericht
TIB: AC 5912. / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Supplement 1: Indistinguishable single photons with flexible electronic triggering
Supplemental-document Originally published in Optica on 20 May 2016 (optica-3-5-493