22 research outputs found
Fabrication And Optical Properties Of Strain-free Self-assembled Mesoscopic Gaas Structures
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)We use a combined process of Ga-assisted deoxidation and local droplet etching to fabricate unstrained mesoscopic GaAs/AlGaAs structures exhibiting a high shape anisotropy with a length up to 1.2 mu m and a width of 150 nm. We demonstrate good controllability over size and morphology of the mesoscopic structures by tuning the growth parameters. Our growth method yields structures, which are coupled to a surrounding quantum well and present unique optical emission features. Microscopic and optical analysis of single structures allows us to demonstrate that single structure emission originates from two different confinement regions, which are spectrally separated and show sharp excitonic lines. Photoluminescence is detected up to room temperature making the structures the ideal candidates for strain-free light emitting/detecting devices.12SisNano (MCTI Brazil)FAPESP [2012/11382-9, 2014/17141-9, 2015/08344-6, 2016/14001-7]CNPq [482729/2013-9, 305769/2015-4, 475343/2013-1]CAPESFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES
Strain-Tunable GaAs Quantum dot: A Nearly Dephasing-Free Source of Entangled Photon Pairs on Demand
Entangled photon generation from semiconductor quantum dots via the
biexciton-exciton cascade underlies various decoherence mechanisms related to
the solid-state nature of the quantum emitters. So far, this has prevented the
demonstration of nearly-maximally entangled photons without the aid of
inefficient and complex post-selection techniques that are hardly suitable for
quantum communication technologies. Here, we tackle this challenge using
strain-tunable GaAs quantum dots driven under two-photon resonant excitation
and with strictly-degenerate exciton states. We demonstrate experimentally that
our on-demand source generates polarization-entangled photons with fidelity of
0.978(5) and concurrence of 0.97(1) without resorting to post-selection
techniques. Moreover, we show that the remaining decoherence mechanisms can be
overcome using a modest Purcell enhancement so as to achieve a degree of
entanglement >0.99. Our results highlight that GaAs quantum dots can be readily
used in advanced communication protocols relying on the non-local properties of
quantum entanglement
On-demand generation of background--free single photons from a solid-state source
True on--demand high--repetition--rate single--photon sources are highly
sought after for quantum information processing applications. However, any
coherently driven two-level quantum system suffers from a finite re-excitation
probability under pulsed excitation, causing undesirable multi--photon
emission. Here, we present a solid--state source of on--demand single photons
yielding a raw second--order coherence of
without any background subtraction nor data processing. To this date, this is
the lowest value of reported for any single--photon source even
compared to the previously best background subtracted values. We achieve this
result on GaAs/AlGaAs quantum dots embedded in a low--Q planar cavity by
employing (i) a two--photon excitation process and (ii) a filtering and
detection setup featuring two superconducting single--photon detectors with
ultralow dark-count rates of and , respectively. Re--excitation processes are dramatically suppressed by
(i), while (ii) removes false coincidences resulting in a negligibly low noise
floor
Intermediate Field Coupling of Single Epitaxial Quantum Dots to Plasmonic Waveguides
Key requirements for quantum plasmonic nanocircuits are reliable
single-photon sources, high coupling efficiency to the plasmonic structures and
low propagation losses. Self-assembled epitaxially grown GaAs quantum dots are
close to ideal stable, bright and narrowband single-photon emitters. Likewise,
wet-chemically grown monocrystalline silver nanowires are among the best
plasmonic waveguides. However, large propagation losses of surface plasmons on
the high-index GaAs substrate prevent their direct combination. Here, we show
by experiment and simulation that the best overall performance of the quantum
plasmonic nanocircuit based on these building blocks is achieved in the
intermediate field regime with an additional spacer layer between the quantum
dot and the plasmonic waveguide. High-resolution cathodoluminescence
measurements allow a precise determination of the coupling distance and support
a simple analytical model to explain the overall performance. The coupling
efficiency is increased up to four times by standing wave interference near the
end of the waveguide.Comment: Accepted at ACS Nano Letters; contains main text and supporting
informatio
Resonance fluorescence of GaAs quantum dots with near-unity photon indistinguishability
Photonic quantum technologies call for scalable quantum light sources that
can be integrated, while providing the end user with single and entangled
photons on-demand. One promising candidate are strain free GaAs/AlGaAs quantum
dots obtained by droplet etching. Such quantum dots exhibit ultra low
multi-photon probability and an unprecedented degree of photon pair
entanglement. However, different to commonly studied InGaAs/GaAs quantum dots
obtained by the Stranski-Krastanow mode, photons with a near-unity
indistinguishability from these quantum emitters have proven to be elusive so
far. Here, we show on-demand generation of near-unity indistinguishable photons
from these quantum emitters by exploring pulsed resonance fluorescence. Given
the short intrinsic lifetime of excitons confined in the GaAs quantum dots, we
show single photon indistinguishability with a raw visibility of
, without the need for Purcell enhancement. Our
results represent a milestone in the advance of GaAs quantum dots by
demonstrating the final missing property standing in the way of using these
emitters as a key component in quantum communication applications, e.g. as an
entangled source for quantum repeater architectures
Highly indistinguishable single photons from droplet-etched GaAs quantum dots integrated in single-mode waveguides and beamsplitters
The integration of on-demand quantum emitters into photonic integrated
circuits (PICs) has drawn much of attention in recent years, as it promises a
scalable implementation of quantum information schemes. A central property for
several applications is the indistinguishability of the emitted photons. In
this regard, GaAs quantum dots (QDs) obtained by droplet etching epitaxy show
excellent performances with visibilities close to one for both individual and
remote emitters. Therefore, the realization of these QDs into PICs is highly
appealing. Here, we show the first implementation in this direction, realizing
the key passive elements needed in PICs, i.e. single-mode waveguides (WGs) with
integrated GaAs-QDs, which can be coherently controlled, as well as
beamsplitters. We study both the statistical distribution of wavelength,
linewidth and decay times of the excitonic line of multiple QDs, as well as the
quantum optical properties of individual emitters under resonant excitation.
Here, we achieve single-photon purities as high as
as well as two-photon interference
visibilities of up to V for two consecutively
emitted photons
Compact Chirped Fiber Bragg Gratings for Single-Photon Generation from Quantum Dots
A scalable source of single photons is a key constituent of an efficient
quantum photonic architecture. To realize this, it is beneficial to have an
ensemble of quantum emitters that can be collectively excited with high
efficiency. Semiconductor quantum dots hold great potential in this context,
due to their excellent photophysical properties. Spectral variability of
quantum dots is commonly regarded as a drawback introduced by the fabrication
method. However, this is beneficial to realize a frequency-multiplexed
single-photon platform. Chirped pulse excitation, relying on the so-called
adiabatic rapid passage, is the most efficient scheme to excite a quantum dot
ensemble due to its immunity to individual quantum dot parameters. Yet, the
existing methods of generating chirped laser pulses to excite a quantum emitter
are bulky, lossy, and mechanically unstable, which severely hampers the
prospects of a quantum dot photon source. Here, we present a compact, robust,
and high-efficiency alternative for chirped pulse excitation of solid-state
quantum emitters. Our simple plug-and-play module consists of chirped fiber
Bragg gratings (CFBGs), fabricated via femtosecond inscription, to provide high
values of dispersion in the near-infrared spectral range, where the quantum
dots emit. We characterize and benchmark the performance of our method via
chirped excitation of a GaAs quantum dot, establishing high-fidelity
single-photon generation. Our highly versatile chirping module coupled to a
photon source is a significant milestone toward realizing practical quantum
photonic devices
The crux of using the cascaded emission of a 3-level quantum ladder system to generate indistinguishable photons
We investigate the degree of indistinguishability of cascaded photons emitted
from a 3-level quantum ladder system; in our case the biexciton-exciton cascade
of semiconductor quantum dots. For the 3-level quantum ladder system we
theoretically demonstrate that the indistinguishability is inherently limited
for both emitted photons and determined by the ratio of the lifetimes of the
excited and intermediate states. We experimentally confirm this finding by
comparing the quantum interference visibility of non-cascaded emission and
cascaded emission from the same semiconductor quantum dot. Quantum optical
simulations produce very good agreement with the measurements and allow to
explore a large parameter space. Based on our model, we propose photonic
structures to optimize the lifetime ratio and overcome the limited
indistinguishability of cascaded photon emission from a 3-level quantum ladder
system.Comment: We moved the paragraph about asymmetric Purcell enhancement from page
4 bottom to page 5 first colum