31 research outputs found
A circular dielectric grating for vertical extraction of single quantum dot emission
We demonstrate a nanostructure composed of partially etched annular trenches
in a suspended GaAs membrane, designed for efficient and moderately broadband
(approx. 5 nm) emission extraction from single InAs quantum dots. Simulations
indicate that a dipole embedded in the nanostructure center radiates upwards
into free space with a nearly Gaussian far-field, allowing a collection
efficiency > 80 % with a high numerical aperture (NA=0.7) optic, and with 12X
Purcell radiative rate enhancement. Fabricated devices exhibit an approx. 10 %
photon collection efficiency with a NA=0.42 objective, a 20X improvement over
quantum dots in unpatterned GaAs. A fourfold exciton lifetime reduction
indicates moderate Purcell enhancement.Comment: (3 pages
Efficient quantum dot single photon extraction into an optical fiber using a nanophotonic directional coupler
We demonstrate a spectrally broadband and effcient technique for collecting
photoluminescence from a single InAs quantum dot directly into a standard
single mode optical fiber. In this approach, an optical fiber taper waveguide
is placed in contact with a suspended GaAs nanophotonic waveguide with embedded
quantum dots, forming an effcient and broadband directional coupler with
standard optical fiber input and output. Effcient photoluminescence collection
over a wavelength range of tens of nanometers is demonstrated, and a maximum
collection effciency of 6.05 % (corresponding single photon rate of 3.0 MHz)
into a single mode optical fiber was estimated for a single quantum dot
exciton
Long Distance Coupling of a Quantum Mechanical Oscillator to the Internal States of an Atomic Ensemble
We propose and investigate a hybrid optomechanical system consisting of a
micro-mechanical oscillator coupled to the internal states of a distant
ensemble of atoms. The interaction between the systems is mediated by a light
field which allows to couple the two systems in a modular way over long
distances. Coupling to internal degrees of freedom of atoms opens up the
possibility to employ high-frequency mechanical resonators in the MHz to GHz
regime, such as optomechanical crystal structures, and to benefit from the rich
toolbox of quantum control over internal atomic states. Previous schemes
involving atomic motional states are rather limited in both of these aspects.
We derive a full quantum model for the effective coupling including the main
sources of decoherence. As an application we show that sympathetic ground-state
cooling and strong coupling between the two systems is possible.Comment: 14 pages, 5 figure
Externally mode-matched cavity quantum electrodynamics with charge-tunable quantum dots
We present coherent reflection spectroscopy on a charge and DC Stark tunable
quantum dot embedded in a high-quality and externally mode-matched microcavity.
The addition of an exciton to a single-electron charged quantum dot forms a
trion that interacts with the microcavity just below strong coupling regime of
cavity quantum electrodynamics. Such an integrated, monolithic system is a
crucial step towards the implementation of scalable hybrid quantum information
schemes that are based on an efficient interaction between a single photon and
a confined electron spin.Comment: 10 pages, 4 figure
Self-tuned quantum dot gain in photonic crystal lasers
We demonstrate that very few (1 to 3) quantum dots as a gain medium are
sufficient to realize a photonic crystal laser based on a high-quality
nanocavity. Photon correlation measurements show a transition from a thermal to
a coherent light state proving that lasing action occurs at ultra-low
thresholds. Observation of lasing is unexpected since the cavity mode is in
general not resonant with the discrete quantum dot states and emission at those
frequencies is suppressed. In this situation, the quasi-continuous quantum dot
states become crucial since they provide an energy-transfer channel into the
lasing mode, effectively leading to a self-tuned resonance for the gain medium.Comment: 4 pages, 4 figures, submitted to Phys. Re
Frequency control of photonic crystal membrane resonators by mono-layer deposition
We study the response of GaAs photonic crystal membrane resonators to thin
film deposition. Slow spectral shifts of the cavity mode of several nanometers
are observed at low temperatures, caused by cryo-gettering of background
molecules. Heating the membrane resets the drift and shielding will prevent
drift altogether. In order to explore the drift as a tool to detect surface
layers, or to intentionally shift the cavity resonance frequency, we studied
the effect of self-assembled monolayers of polypeptide molecules attached to
the membranes. The 2 nm thick monolayers lead to a discrete step in the
resonance frequency and partially passivate the surface.Comment: 3 pages, 4 figures, submitted to Appl. Phys. Let
Improving the performance of bright quantum dot single photon sources using amplitude modulation
Single epitaxially-grown semiconductor quantum dots have great potential as
single photon sources for photonic quantum technologies, though in practice
devices often exhibit non-ideal behavior. Here, we demonstrate that amplitude
modulation can improve the performance of quantum-dot-based sources. Starting
with a bright source consisting of a single quantum dot in a fiber-coupled
microdisk cavity, we use synchronized amplitude modulation to temporally filter
the emitted light. We observe that the single photon purity, temporal overlap
between successive emission events, and indistinguishability can be greatly
improved with this technique. As this method can be applied to any triggered
single photon source, independent of geometry and after device fabrication, it
is a flexible approach to improve the performance of solid-state systems, which
often suffer from excess dephasing and multi-photon background emission